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-
-
-
-
-
-
-Network Working Group M. Allman
-Request for Comments: 2428 NASA Lewis/Sterling Software
-Category: Standards Track S. Ostermann
- Ohio University
- C. Metz
- The Inner Net
- September 1998
-
-
- FTP Extensions for IPv6 and NATs
-
-Status of this Memo
-
- This document specifies an Internet standards track protocol for the
- Internet community, and requests discussion and suggestions for
- improvements. Please refer to the current edition of the "Internet
- Official Protocol Standards" (STD 1) for the standardization state
- and status of this protocol. Distribution of this memo is unlimited.
-
-Copyright Notice
-
- Copyright (C) The Internet Society (1998). All Rights Reserved.
-
-Abstract
-
- The specification for the File Transfer Protocol assumes that the
- underlying network protocol uses a 32-bit network address
- (specifically IP version 4). With the deployment of version 6 of the
- Internet Protocol, network addresses will no longer be 32-bits. This
- paper specifies extensions to FTP that will allow the protocol to
- work over IPv4 and IPv6. In addition, the framework defined can
- support additional network protocols in the future.
-
-1. Introduction
-
- The keywords, such as MUST and SHOULD, found in this document are
- used as defined in RFC 2119 [Bra97].
-
- The File Transfer Protocol [PR85] only provides the ability to
- communicate information about IPv4 data connections. FTP assumes
- network addresses will be 32 bits in length. However, with the
- deployment of version 6 of the Internet Protocol [DH96] addresses
- will no longer be 32 bits long. RFC 1639 [Pis94] specifies
- extensions to FTP to enable its use over various network protocols.
- Unfortunately, the mechanism can fail in a multi-protocol
- environment. During the transition between IPv4 and IPv6, FTP needs
- the ability to negotiate the network protocol that will be used for
- data transfer.
-
-
-
-Allman, et. al. Standards Track [Page 1]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
- This document provides a specification for a way that FTP can
- communicate data connection endpoint information for network
- protocols other than IPv4. In this specification, the FTP commands
- PORT and PASV are replaced with EPRT and EPSV, respectively. This
- document is organized as follows. Section 2 outlines the EPRT
- command and Section 3 outlines the EPSV command. Section 4 defines
- the utilization of these two new FTP commands. Section 5 briefly
- presents security considerations. Finally, Section 6 provides
- conclusions.
-
-2. The EPRT Command
-
- The EPRT command allows for the specification of an extended address
- for the data connection. The extended address MUST consist of the
- network protocol as well as the network and transport addresses. The
- format of EPRT is:
-
- EPRT<space><d><net-prt><d><net-addr><d><tcp-port><d>
-
- The EPRT command keyword MUST be followed by a single space (ASCII
- 32). Following the space, a delimiter character (<d>) MUST be
- specified. The delimiter character MUST be one of the ASCII
- characters in range 33-126 inclusive. The character "|" (ASCII 124)
- is recommended unless it coincides with a character needed to encode
- the network address.
-
- The <net-prt> argument MUST be an address family number defined by
- IANA in the latest Assigned Numbers RFC (RFC 1700 [RP94] as of the
- writing of this document). This number indicates the protocol to be
- used (and, implicitly, the address length). This document will use
- two of address family numbers from [RP94] as examples, according to
- the following table:
-
- AF Number Protocol
- --------- --------
- 1 Internet Protocol, Version 4 [Pos81a]
- 2 Internet Protocol, Version 6 [DH96]
-
- The <net-addr> is a protocol specific string representation of the
- network address. For the two address families specified above (AF
- Number 1 and 2), addresses MUST be in the following format:
-
- AF Number Address Format Example
- --------- -------------- -------
- 1 dotted decimal 132.235.1.2
- 2 IPv6 string 1080::8:800:200C:417A
- representations
- defined in [HD96]
-
-
-
-Allman, et. al. Standards Track [Page 2]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
- The <tcp-port> argument must be the string representation of the
- number of the TCP port on which the host is listening for the data
- connection.
-
- The following are sample EPRT commands:
-
- EPRT |1|132.235.1.2|6275|
-
- EPRT |2|1080::8:800:200C:417A|5282|
-
- The first command specifies that the server should use IPv4 to open a
- data connection to the host "132.235.1.2" on TCP port 6275. The
- second command specifies that the server should use the IPv6 network
- protocol and the network address "1080::8:800:200C:417A" to open a
- TCP data connection on port 5282.
-
- Upon receipt of a valid EPRT command, the server MUST return a code
- of 200 (Command OK). The standard negative error code 500 and 501
- [PR85] are sufficient to handle most errors (e.g., syntax errors)
- involving the EPRT command. However, an additional error code is
- needed. The response code 522 indicates that the server does not
- support the requested network protocol. The interpretation of this
- new error code is:
-
- 5yz Negative Completion
- x2z Connections
- xy2 Extended Port Failure - unknown network protocol
-
- The text portion of the response MUST indicate which network
- protocols the server does support. If the network protocol is
- unsupported, the format of the response string MUST be:
-
- <text stating that the network protocol is unsupported> \
- (prot1,prot2,...,protn)
-
- Both the numeric code specified above and the protocol information
- between the characters '(' and ')' are intended for the software
- automata receiving the response; the textual message between the
- numeric code and the '(' is intended for the human user and can be
- any arbitrary text, but MUST NOT include the characters '(' and ')'.
- In the above case, the text SHOULD indicate that the network protocol
- in the EPRT command is not supported by the server. The list of
- protocols inside the parenthesis MUST be a comma separated list of
- address family numbers. Two example response strings follow:
-
- Network protocol not supported, use (1)
-
- Network protocol not supported, use (1,2)
-
-
-
-Allman, et. al. Standards Track [Page 3]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
-3. The EPSV Command
-
- The EPSV command requests that a server listen on a data port and
- wait for a connection. The EPSV command takes an optional argument.
- The response to this command includes only the TCP port number of the
- listening connection. The format of the response, however, is
- similar to the argument of the EPRT command. This allows the same
- parsing routines to be used for both commands. In addition, the
- format leaves a place holder for the network protocol and/or network
- address, which may be needed in the EPSV response in the future. The
- response code for entering passive mode using an extended address
- MUST be 229. The interpretation of this code, according to [PR85]
- is:
-
- 2yz Positive Completion
- x2z Connections
- xy9 Extended Passive Mode Entered
-
- The text returned in response to the EPSV command MUST be:
-
- <text indicating server is entering extended passive mode> \
- (<d><d><d><tcp-port><d>)
-
- The portion of the string enclosed in parentheses MUST be the exact
- string needed by the EPRT command to open the data connection, as
- specified above.
-
- The first two fields contained in the parenthesis MUST be blank. The
- third field MUST be the string representation of the TCP port number
- on which the server is listening for a data connection. The network
- protocol used by the data connection will be the same network
- protocol used by the control connection. In addition, the network
- address used to establish the data connection will be the same
- network address used for the control connection. An example response
- string follows:
-
- Entering Extended Passive Mode (|||6446|)
-
- The standard negative error codes 500 and 501 are sufficient to
- handle all errors involving the EPSV command (e.g., syntax errors).
-
- When the EPSV command is issued with no argument, the server will
- choose the network protocol for the data connection based on the
- protocol used for the control connection. However, in the case of
- proxy FTP, this protocol might not be appropriate for communication
- between the two servers. Therefore, the client needs to be able to
- request a specific protocol. If the server returns a protocol that
- is not supported by the host that will be connecting to the port, the
-
-
-
-Allman, et. al. Standards Track [Page 4]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
- client MUST issue an ABOR (abort) command to allow the server to
- close down the listening connection. The client can then send an
- EPSV command requesting the use of a specific network protocol, as
- follows:
-
- EPSV<space><net-prt>
-
- If the requested protocol is supported by the server, it SHOULD use
- the protocol. If not, the server MUST return the 522 error messages
- as outlined in section 2.
-
- Finally, the EPSV command can be used with the argument "ALL" to
- inform Network Address Translators that the EPRT command (as well as
- other data commands) will no longer be used. An example of this
- command follows:
-
- EPSV<space>ALL
-
- Upon receipt of an EPSV ALL command, the server MUST reject all data
- connection setup commands other than EPSV (i.e., EPRT, PORT, PASV, et
- al.). This use of the EPSV command is further explained in section
- 4.
-
-4. Command Usage
-
- For all FTP transfers where the control and data connection(s) are
- being established between the same two machines, the EPSV command
- MUST be used. Using the EPSV command benefits performance of
- transfers that traverse firewalls or Network Address Translators
- (NATs). RFC 1579 [Bel94] recommends using the passive command when
- behind firewalls since firewalls do not generally allow incoming
- connections (which are required when using the PORT (EPRT) command).
- In addition, using EPSV as defined in this document does not require
- NATs to change the network address in the traffic as it is forwarded.
- The NAT would have to change the address if the EPRT command was
- used. Finally, if the client issues an "EPSV ALL" command, NATs may
- be able to put the connection on a "fast path" through the
- translator, as the EPRT command will never be used and therefore,
- translation of the data portion of the segments will never be needed.
- When a client only expects to do two-way FTP transfers, it SHOULD
- issue this command as soon as possible. If a client later finds that
- it must do a three-way FTP transfer after issuing an EPSV ALL
- command, a new FTP session MUST be started.
-
-
-
-
-
-
-
-
-Allman, et. al. Standards Track [Page 5]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
-5. Security Issues
-
- The authors do not believe that these changes to FTP introduce new
- security problems. A companion Work in Progress [AO98] is a more
- general discussion of FTP security issues and techniques to reduce
- these security problems.
-
-6. Conclusions
-
- The extensions specified in this paper will enable FTP to operate
- over a variety of network protocols.
-
-References
-
- [AO98] Allman, M., and S. Ostermann, "FTP Security
- Considerations", Work in Progress.
-
- [Bel94] Bellovin, S., "Firewall-Friendly FTP", RFC 1579, February
- 1994.
-
- [Bra97] Bradner, S., "Key words for use in RFCs to Indicate
- Requirement Levels", BCP 14, RFC 2119, March 1997.
-
- [DH96] Deering, S., and R. Hinden, "Internet Protocol, Version 6
- (IPv6) Specification", RFC 1883, December 1995.
-
- [HD96] Hinden, R., and S. Deering, "IP Version 6 Addressing
- Architecture", RFC 2373, July 1998.
-
- [Pis94] Piscitello, D., "FTP Operation Over Big Address Records
- (FOOBAR)", RFC 1639, June 1994.
-
- [Pos81a] Postel, J., "Internet Protocol", STD 5, RFC 791, September
- 1981.
-
- [Pos81b] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
- September 1981.
-
- [PR85] Postel, J., and J. Reynolds, "File Transfer Protocol (FTP)",
- STD 9, RFC 959, October 1985.
-
- [RP94] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
- 1700, October 1994. See also:
- http://www.iana.org/numbers.html
-
-
-
-
-
-
-
-Allman, et. al. Standards Track [Page 6]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
-Authors' Addresses
-
- Mark Allman
- NASA Lewis Research Center/Sterling Software
- 21000 Brookpark Rd. MS 54-2
- Cleveland, OH 44135
-
- Phone: (216) 433-6586
- http://gigahertz.lerc.nasa.gov/~mallman/
-
-
- Shawn Ostermann
- School of Electrical Engineering and Computer Science
- Ohio University
- 416 Morton Hall
- Athens, OH 45701
-
- Phone: (740) 593-1234
-
-
- Craig Metz
- The Inner Net
- Box 10314-1954
- Blacksburg, VA 24062-0314
-
- Phone: (DSN) 754-8590
-
-
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-Allman, et. al. Standards Track [Page 7]
-
-RFC 2428 FTP Extensions for IPv6 and NATs September 1998
-
-
-Full Copyright Statement
-
- Copyright (C) The Internet Society (1998). All Rights Reserved.
-
- This document and translations of it may be copied and furnished to
- others, and derivative works that comment on or otherwise explain it
- or assist in its implementation may be prepared, copied, published
- and distributed, in whole or in part, without restriction of any
- kind, provided that the above copyright notice and this paragraph are
- included on all such copies and derivative works. However, this
- document itself may not be modified in any way, such as by removing
- the copyright notice or references to the Internet Society or other
- Internet organizations, except as needed for the purpose of
- developing Internet standards in which case the procedures for
- copyrights defined in the Internet Standards process must be
- followed, or as required to translate it into languages other than
- English.
-
- The limited permissions granted above are perpetual and will not be
- revoked by the Internet Society or its successors or assigns.
-
- This document and the information contained herein is provided on an
- "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
- TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
- BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
- HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
- MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
-
-
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-Allman, et. al. Standards Track [Page 8]
-
diff --git a/lib/inets/doc/archive/rfc2577.txt b/lib/inets/doc/archive/rfc2577.txt
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-
-
-
-
-
-
-Network Working Group M. Allman
-Request for Comments: 2577 NASA Glenn/Sterling Software
-Category: Informational S. Ostermann
- Ohio University
- May 1999
-
-
- FTP Security Considerations
-
-Status of this Memo
-
- This memo provides information for the Internet community. It does
- not specify an Internet standard of any kind. Distribution of this
- memo is unlimited.
-
-Copyright Notice
-
- Copyright (C) The Internet Society (1999). All Rights Reserved.
-
-Abstract
-
- The specification for the File Transfer Protocol (FTP) contains a
- number of mechanisms that can be used to compromise network security.
- The FTP specification allows a client to instruct a server to
- transfer files to a third machine. This third-party mechanism, known
- as proxy FTP, causes a well known security problem. The FTP
- specification also allows an unlimited number of attempts at entering
- a user's password. This allows brute force "password guessing"
- attacks. This document provides suggestions for system
- administrators and those implementing FTP servers that will decrease
- the security problems associated with FTP.
-
-1 Introduction
-
- The File Transfer Protocol specification (FTP) [PR85] provides a
- mechanism that allows a client to establish an FTP control connection
- and transfer a file between two FTP servers. This "proxy FTP"
- mechanism can be used to decrease the amount of traffic on the
- network; the client instructs one server to transfer a file to
- another server, rather than transferring the file from the first
- server to the client and then from the client to the second server.
- This is particularly useful when the client connects to the network
- using a slow link (e.g., a modem). While useful, proxy FTP provides
- a security problem known as a "bounce attack" [CERT97:27]. In
- addition to the bounce attack, FTP servers can be used by attackers
- to guess passwords using brute force.
-
-
-
-
-
-Allman & Ostermann Informational [Page 1]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
- This document does not contain a discussion of FTP when used in
- conjunction with strong security protocols, such as IP Security.
- These security concerns should be documented, however they are out of
- the scope of this document.
-
- This paper provides information for FTP server implementers and
- system administrators, as follows. Section 2 describes the FTP
- "bounce attack". Section 3 provides suggestions for minimizing the
- bounce attack. Section 4 provides suggestions for servers which
- limit access based on network address. Section 5 provides
- recommendations for limiting brute force "password guessing" by
- clients. Next, section 6 provides a brief discussion of mechanisms
- to improve privacy. Section 7 provides a mechanism to prevent user
- identity guessing. Section 8 discusses the practice of port
- stealing. Finally, section 9 provides an overview of other FTP
- security issues related to software bugs rather than protocol issues.
-
-2 The Bounce Attack
-
- The version of FTP specified in the standard [PR85] provides a method
- for attacking well known network servers, while making the
- perpetrators difficult to track down. The attack involves sending an
- FTP "PORT" command to an FTP server containing the network address
- and the port number of the machine and service being attacked. At
- this point, the original client can instruct the FTP server to send a
- file to the service being attacked. Such a file would contain
- commands relevant to the service being attacked (SMTP, NNTP, etc.).
- Instructing a third party to connect to the service, rather than
- connecting directly, makes tracking down the perpetrator difficult
- and can circumvent network-address-based access restrictions.
-
- As an example, a client uploads a file containing SMTP commands to an
- FTP server. Then, using an appropriate PORT command, the client
- instructs the server to open a connection to a third machine's SMTP
- port. Finally, the client instructs the server to transfer the
- uploaded file containing SMTP commands to the third machine. This
- may allow the client to forge mail on the third machine without
- making a direct connection. This makes it difficult to track
- attackers.
-
-3 Protecting Against the Bounce Attack
-
- The original FTP specification [PR85] assumes that data connections
- will be made using the Transmission Control Protocol (TCP) [Pos81].
- TCP port numbers in the range 0 - 1023 are reserved for well known
- services such as mail, network news and FTP control connections
- [RP94]. The FTP specification makes no restrictions on the TCP port
- number used for the data connection. Therefore, using proxy FTP,
-
-
-
-Allman & Ostermann Informational [Page 2]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
- clients have the ability to tell the server to attack a well known
- service on any machine.
-
- To avoid such bounce attacks, it is suggested that servers not open
- data connections to TCP ports less than 1024. If a server receives a
- PORT command containing a TCP port number less than 1024, the
- suggested response is 504 (defined as "Command not implemented for
- that parameter" by [PR85]). Note that this still leaves non-well
- known servers (those running on ports greater than 1023) vulnerable
- to bounce attacks.
-
- Several proposals (e.g., [AOM98] and [Pis94]) provide a mechanism
- that would allow data connections to be made using a transport
- protocol other than TCP. Similar precautions should be taken to
- protect well known services when using these protocols.
-
- Also note that the bounce attack generally requires that a
- perpetrator be able to upload a file to an FTP server and later
- download it to the service being attacked. Using proper file
- protections will prevent this behavior. However, attackers can also
- attack services by sending random data from a remote FTP server which
- may cause problems for some services.
-
- Disabling the PORT command is also an option for protecting against
- the bounce attack. Most file transfers can be made using only the
- PASV command [Bel94]. The disadvantage of disabling the PORT command
- is that one loses the ability to use proxy FTP, but proxy FTP may not
- be necessary in a particular environment.
-
-4 Restricted Access
-
- For some FTP servers, it is desirable to restrict access based on
- network address. For example, a server might want to restrict access
- to certain files from certain places (e.g., a certain file should not
- be transferred out of an organization). In such a situation, the
- server should confirm that the network address of the remote hosts on
- both the control connection and the data connection are within the
- organization before sending a restricted file. By checking both
- connections, a server is protected against the case when the control
- connection is established with a trusted host and the data connection
- is not. Likewise, the client should verify the IP address of the
- remote host after accepting a connection on a port opened in listen
- mode to verify that the connection was made by the expected server.
-
- Note that restricting access based on network address leaves the FTP
- server vulnerable to "spoof" attacks. In a spoof attack, for
- example, an attacking machine could assume the host address of
- another machine inside an organization and download files that are
-
-
-
-Allman & Ostermann Informational [Page 3]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
- not accessible from outside the organization. Whenever possible,
- secure authentication mechanisms should be used, such as those
- outlined in [HL97].
-
-5 Protecting Passwords
-
- To minimize the risk of brute force password guessing through the FTP
- server, it is suggested that servers limit the number of attempts
- that can be made at sending a correct password. After a small number
- of attempts (3-5), the server should close the control connection
- with the client. Before closing the control connection the server
- must send a return code of 421 ("Service not available, closing
- control connection." [PR85]) to the client. In addition, it is
- suggested that the server impose a 5 second delay before replying to
- an invalid "PASS" command to diminish the efficiency of a brute force
- attack. If available, mechanisms already provided by the target
- operating system should be used to implement the above suggestions.
-
- An intruder can subvert the above mechanisms by establishing
- multiple, parallel control connections to a server. To combat the
- use of multiple concurrent connections, the server could either limit
- the total number of control connections possible or attempt to detect
- suspicious activity across sessions and refuse further connections
- from the site. However, both of these mechanisms open the door to
- "denial of service" attacks, in which an attacker purposely initiates
- the attack to disable access by a valid user.
-
- Standard FTP [PR85] sends passwords in clear text using the "PASS"
- command. It is suggested that FTP clients and servers use alternate
- authentication mechanisms that are not subject to eavesdropping (such
- as the mechanisms being developed by the IETF Common Authentication
- Technology Working Group [HL97]).
-
-6 Privacy
-
- All data and control information (including passwords) is sent across
- the network in unencrypted form by standard FTP [PR85]. To guarantee
- the privacy of the information FTP transmits, a strong encryption
- scheme should be used whenever possible. One such mechanism is
- defined in [HL97].
-
-7 Protecting Usernames
-
- Standard FTP [PR85] specifies a 530 response to the USER command when
- the username is rejected. If the username is valid and a password is
- required FTP returns a 331 response instead. In order to prevent a
- malicious client from determining valid usernames on a server, it is
- suggested that a server always return 331 to the USER command and
-
-
-
-Allman & Ostermann Informational [Page 4]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
- then reject the combination of username and password for an invalid
- username.
-
-8 Port Stealing
-
- Many operating systems assign dynamic port numbers in increasing
- order. By making a legitimate transfer, an attacker can observe the
- current port number allocated by the server and "guess" the next one
- that will be used. The attacker can make a connection to this port,
- thus denying another legitimate client the ability to make a
- transfer. Alternatively, the attacker can steal a file meant for a
- legitimate user. In addition, an attacker can insert a forged file
- into a data stream thought to come from an authenticated client.
- This problem can be mitigated by making FTP clients and servers use
- random local port numbers for data connections, either by requesting
- random ports from the operating system or using system dependent
- mechanisms.
-
-9 Software-Base Security Problems
-
- The emphasis in this document is on protocol-related security issues.
- There are a number of documented FTP security-related problems that
- are due to poor implementation as well. Although the details of
- these types of problems are beyond the scope of this document, it
- should be pointed out that the following FTP features has been abused
- in the past and should be treated with great care by future
- implementers:
-
- Anonymous FTP
-
- Anonymous FTP refers to the ability of a client to connect to an
- FTP server with minimal authentication and gain access to public
- files. Security problems arise when such a user can read all
- files on the system or can create files. [CERT92:09] [CERT93:06]
-
- Remote Command Execution
-
- An optional FTP extension, "SITE EXEC", allows clients to execute
- arbitrary commands on the server. This feature should obviously
- be implemented with great care. There are several documented
- cases of the FTP "SITE EXEC" command being used to subvert server
- security [CERT94:08] [CERT95:16]
-
- Debug Code
-
- Several previous security compromises related to FTP can be
- attributed to software that was installed with debugging features
- enabled [CERT88:01].
-
-
-
-Allman & Ostermann Informational [Page 5]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
- This document recommends that implementors of FTP servers with these
- capabilities review all of the CERT advisories for attacks on these
- or similar mechanisms before releasing their software.
-
-10 Conclusion
-
- Using the above suggestions can decrease the security problems
- associated with FTP servers without eliminating functionality.
-
-11 Security Considerations
-
- Security issues are discussed throughout this memo.
-
-Acknowledgments
-
- We would like to thank Alex Belits, Jim Bound, William Curtin, Robert
- Elz, Paul Hethmon, Alun Jones and Stephen Tihor for their helpful
- comments on this paper. Also, we thank the FTPEXT WG members who
- gave many useful suggestions at the Memphis IETF meeting.
-
-References
-
- [AOM98] Allman, M., Ostermann, S. and C. Metz, "FTP Extensions
- for IPv6 and NATs", RFC 2428, September 1998.
-
- [Bel94] Bellovin. S., "Firewall-Friendly FTP", RFC 1579, February
- 1994.
-
- [CERT88:01] CERT Advisory CA-88:01. ftpd Vulnerability. December,
- 1988 ftp://info.cert.org/pub/cert_advisories/
-
- [CERT92:09] CERT Advisory CA-92:09. AIX Anonymous FTP Vulnerability.
- April 27, 1992. ftp://info.cert.org/pub/cert_advisories/
-
- [CERT93:06] CERT Advisory CA-93:06. Wuarchive ftpd Vulnerability.
- September 19,1997
- ftp://info.cert.org/pub/cert_advisories/
-
- [CERT94:08] CERT Advisory CA-94:08. ftpd Vulnerabilities. September
- 23, 1997. ftp://info.cert.org/pub/cert_advisories/
-
- [CERT95:16] CERT Advisory CA-95:16. wu-ftpd Misconfiguration
- Vulnerability. September 23, 1997
- ftp://info.cert.org/pub/cert_advisories/
-
- [CERT97:27] CERT Advisory CA-97.27. FTP Bounce. January 8, 1998.
- ftp://info.cert.org/pub/cert_advisories/
-
-
-
-
-Allman & Ostermann Informational [Page 6]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
- [HL97] Horowitz, M. and S. Lunt, "FTP Security Extensions", RFC
- 2228, October 1997.
-
- [Pis94] Piscitello, D., "FTP Operation Over Big Address Records
- (FOOBAR), RFC 1639, June 1994.
-
- [Pos81] Postel, J., "Transmission Control Protocol", STD 7, RFC
- 793, September 1981.
-
- [PR85] Postel, J. and J. Reynolds, "File Transfer Protocol
- (FTP)", STD 9, RFC 959, October 1985.
-
- [RP94] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2,
- RFC 1700, October 1994. See also:
- http://www.iana.org/numbers.html
-
-Authors' Addresses
-
- Mark Allman
- NASA Glenn Research Center/Sterling Software
- 21000 Brookpark Rd. MS 54-2
- Cleveland, OH 44135
-
-
-
- Shawn Ostermann
- School of Electrical Engineering and Computer Science
- Ohio University
- 416 Morton Hall
- Athens, OH 45701
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Allman & Ostermann Informational [Page 7]
-
-RFC 2577 FTP Security Considerations May 1999
-
-
-Full Copyright Statement
-
- Copyright (C) The Internet Society (1999). All Rights Reserved.
-
- This document and translations of it may be copied and furnished to
- others, and derivative works that comment on or otherwise explain it
- or assist in its implementation may be prepared, copied, published
- and distributed, in whole or in part, without restriction of any
- kind, provided that the above copyright notice and this paragraph are
- included on all such copies and derivative works. However, this
- document itself may not be modified in any way, such as by removing
- the copyright notice or references to the Internet Society or other
- Internet organizations, except as needed for the purpose of
- developing Internet standards in which case the procedures for
- copyrights defined in the Internet Standards process must be
- followed, or as required to translate it into languages other than
- English.
-
- The limited permissions granted above are perpetual and will not be
- revoked by the Internet Society or its successors or assigns.
-
- This document and the information contained herein is provided on an
- "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
- TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
- BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
- HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
- MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
-
-Acknowledgement
-
- Funding for the RFC Editor function is currently provided by the
- Internet Society.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Allman & Ostermann Informational [Page 8]
-
diff --git a/lib/inets/doc/archive/rfc959.txt b/lib/inets/doc/archive/rfc959.txt
deleted file mode 100644
index 5c9f11af5d..0000000000
--- a/lib/inets/doc/archive/rfc959.txt
+++ /dev/null
@@ -1,3933 +0,0 @@
-
-
-Network Working Group J. Postel
-Request for Comments: 959 J. Reynolds
- ISI
-Obsoletes RFC: 765 (IEN 149) October 1985
-
- FILE TRANSFER PROTOCOL (FTP)
-
-
-Status of this Memo
-
- This memo is the official specification of the File Transfer
- Protocol (FTP). Distribution of this memo is unlimited.
-
- The following new optional commands are included in this edition of
- the specification:
-
- CDUP (Change to Parent Directory), SMNT (Structure Mount), STOU
- (Store Unique), RMD (Remove Directory), MKD (Make Directory), PWD
- (Print Directory), and SYST (System).
-
- Note that this specification is compatible with the previous edition.
-
-1. INTRODUCTION
-
- The objectives of FTP are 1) to promote sharing of files (computer
- programs and/or data), 2) to encourage indirect or implicit (via
- programs) use of remote computers, 3) to shield a user from
- variations in file storage systems among hosts, and 4) to transfer
- data reliably and efficiently. FTP, though usable directly by a user
- at a terminal, is designed mainly for use by programs.
-
- The attempt in this specification is to satisfy the diverse needs of
- users of maxi-hosts, mini-hosts, personal workstations, and TACs,
- with a simple, and easily implemented protocol design.
-
- This paper assumes knowledge of the Transmission Control Protocol
- (TCP) [2] and the Telnet Protocol [3]. These documents are contained
- in the ARPA-Internet protocol handbook [1].
-
-2. OVERVIEW
-
- In this section, the history, the terminology, and the FTP model are
- discussed. The terms defined in this section are only those that
- have special significance in FTP. Some of the terminology is very
- specific to the FTP model; some readers may wish to turn to the
- section on the FTP model while reviewing the terminology.
-
-
-
-
-
-
-
-Postel & Reynolds [Page 1]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- 2.1. HISTORY
-
- FTP has had a long evolution over the years. Appendix III is a
- chronological compilation of Request for Comments documents
- relating to FTP. These include the first proposed file transfer
- mechanisms in 1971 that were developed for implementation on hosts
- at M.I.T. (RFC 114), plus comments and discussion in RFC 141.
-
- RFC 172 provided a user-level oriented protocol for file transfer
- between host computers (including terminal IMPs). A revision of
- this as RFC 265, restated FTP for additional review, while RFC 281
- suggested further changes. The use of a "Set Data Type"
- transaction was proposed in RFC 294 in January 1982.
-
- RFC 354 obsoleted RFCs 264 and 265. The File Transfer Protocol
- was now defined as a protocol for file transfer between HOSTs on
- the ARPANET, with the primary function of FTP defined as
- transfering files efficiently and reliably among hosts and
- allowing the convenient use of remote file storage capabilities.
- RFC 385 further commented on errors, emphasis points, and
- additions to the protocol, while RFC 414 provided a status report
- on the working server and user FTPs. RFC 430, issued in 1973,
- (among other RFCs too numerous to mention) presented further
- comments on FTP. Finally, an "official" FTP document was
- published as RFC 454.
-
- By July 1973, considerable changes from the last versions of FTP
- were made, but the general structure remained the same. RFC 542
- was published as a new "official" specification to reflect these
- changes. However, many implementations based on the older
- specification were not updated.
-
- In 1974, RFCs 607 and 614 continued comments on FTP. RFC 624
- proposed further design changes and minor modifications. In 1975,
- RFC 686 entitled, "Leaving Well Enough Alone", discussed the
- differences between all of the early and later versions of FTP.
- RFC 691 presented a minor revision of RFC 686, regarding the
- subject of print files.
-
- Motivated by the transition from the NCP to the TCP as the
- underlying protocol, a phoenix was born out of all of the above
- efforts in RFC 765 as the specification of FTP for use on TCP.
-
- This current edition of the FTP specification is intended to
- correct some minor documentation errors, to improve the
- explanation of some protocol features, and to add some new
- optional commands.
-
-
-Postel & Reynolds [Page 2]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- In particular, the following new optional commands are included in
- this edition of the specification:
-
- CDUP - Change to Parent Directory
-
- SMNT - Structure Mount
-
- STOU - Store Unique
-
- RMD - Remove Directory
-
- MKD - Make Directory
-
- PWD - Print Directory
-
- SYST - System
-
- This specification is compatible with the previous edition. A
- program implemented in conformance to the previous specification
- should automatically be in conformance to this specification.
-
- 2.2. TERMINOLOGY
-
- ASCII
-
- The ASCII character set is as defined in the ARPA-Internet
- Protocol Handbook. In FTP, ASCII characters are defined to be
- the lower half of an eight-bit code set (i.e., the most
- significant bit is zero).
-
- access controls
-
- Access controls define users' access privileges to the use of a
- system, and to the files in that system. Access controls are
- necessary to prevent unauthorized or accidental use of files.
- It is the prerogative of a server-FTP process to invoke access
- controls.
-
- byte size
-
- There are two byte sizes of interest in FTP: the logical byte
- size of the file, and the transfer byte size used for the
- transmission of the data. The transfer byte size is always 8
- bits. The transfer byte size is not necessarily the byte size
- in which data is to be stored in a system, nor the logical byte
- size for interpretation of the structure of the data.
-
-
-
-Postel & Reynolds [Page 3]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- control connection
-
- The communication path between the USER-PI and SERVER-PI for
- the exchange of commands and replies. This connection follows
- the Telnet Protocol.
-
- data connection
-
- A full duplex connection over which data is transferred, in a
- specified mode and type. The data transferred may be a part of
- a file, an entire file or a number of files. The path may be
- between a server-DTP and a user-DTP, or between two
- server-DTPs.
-
- data port
-
- The passive data transfer process "listens" on the data port
- for a connection from the active transfer process in order to
- open the data connection.
-
- DTP
-
- The data transfer process establishes and manages the data
- connection. The DTP can be passive or active.
-
- End-of-Line
-
- The end-of-line sequence defines the separation of printing
- lines. The sequence is Carriage Return, followed by Line Feed.
-
- EOF
-
- The end-of-file condition that defines the end of a file being
- transferred.
-
- EOR
-
- The end-of-record condition that defines the end of a record
- being transferred.
-
- error recovery
-
- A procedure that allows a user to recover from certain errors
- such as failure of either host system or transfer process. In
- FTP, error recovery may involve restarting a file transfer at a
- given checkpoint.
-
-
-
-Postel & Reynolds [Page 4]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- FTP commands
-
- A set of commands that comprise the control information flowing
- from the user-FTP to the server-FTP process.
-
- file
-
- An ordered set of computer data (including programs), of
- arbitrary length, uniquely identified by a pathname.
-
- mode
-
- The mode in which data is to be transferred via the data
- connection. The mode defines the data format during transfer
- including EOR and EOF. The transfer modes defined in FTP are
- described in the Section on Transmission Modes.
-
- NVT
-
- The Network Virtual Terminal as defined in the Telnet Protocol.
-
- NVFS
-
- The Network Virtual File System. A concept which defines a
- standard network file system with standard commands and
- pathname conventions.
-
- page
-
- A file may be structured as a set of independent parts called
- pages. FTP supports the transmission of discontinuous files as
- independent indexed pages.
-
- pathname
-
- Pathname is defined to be the character string which must be
- input to a file system by a user in order to identify a file.
- Pathname normally contains device and/or directory names, and
- file name specification. FTP does not yet specify a standard
- pathname convention. Each user must follow the file naming
- conventions of the file systems involved in the transfer.
-
- PI
-
- The protocol interpreter. The user and server sides of the
- protocol have distinct roles implemented in a user-PI and a
- server-PI.
-
-
-Postel & Reynolds [Page 5]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- record
-
- A sequential file may be structured as a number of contiguous
- parts called records. Record structures are supported by FTP
- but a file need not have record structure.
-
- reply
-
- A reply is an acknowledgment (positive or negative) sent from
- server to user via the control connection in response to FTP
- commands. The general form of a reply is a completion code
- (including error codes) followed by a text string. The codes
- are for use by programs and the text is usually intended for
- human users.
-
- server-DTP
-
- The data transfer process, in its normal "active" state,
- establishes the data connection with the "listening" data port.
- It sets up parameters for transfer and storage, and transfers
- data on command from its PI. The DTP can be placed in a
- "passive" state to listen for, rather than initiate a
- connection on the data port.
-
- server-FTP process
-
- A process or set of processes which perform the function of
- file transfer in cooperation with a user-FTP process and,
- possibly, another server. The functions consist of a protocol
- interpreter (PI) and a data transfer process (DTP).
-
- server-PI
-
- The server protocol interpreter "listens" on Port L for a
- connection from a user-PI and establishes a control
- communication connection. It receives standard FTP commands
- from the user-PI, sends replies, and governs the server-DTP.
-
- type
-
- The data representation type used for data transfer and
- storage. Type implies certain transformations between the time
- of data storage and data transfer. The representation types
- defined in FTP are described in the Section on Establishing
- Data Connections.
-
-
-
-
-Postel & Reynolds [Page 6]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- user
-
- A person or a process on behalf of a person wishing to obtain
- file transfer service. The human user may interact directly
- with a server-FTP process, but use of a user-FTP process is
- preferred since the protocol design is weighted towards
- automata.
-
- user-DTP
-
- The data transfer process "listens" on the data port for a
- connection from a server-FTP process. If two servers are
- transferring data between them, the user-DTP is inactive.
-
- user-FTP process
-
- A set of functions including a protocol interpreter, a data
- transfer process and a user interface which together perform
- the function of file transfer in cooperation with one or more
- server-FTP processes. The user interface allows a local
- language to be used in the command-reply dialogue with the
- user.
-
- user-PI
-
- The user protocol interpreter initiates the control connection
- from its port U to the server-FTP process, initiates FTP
- commands, and governs the user-DTP if that process is part of
- the file transfer.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Postel & Reynolds [Page 7]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- 2.3. THE FTP MODEL
-
- With the above definitions in mind, the following model (shown in
- Figure 1) may be diagrammed for an FTP service.
-
- -------------
- |/---------\|
- || User || --------
- ||Interface|<--->| User |
- |\----^----/| --------
- ---------- | | |
- |/------\| FTP Commands |/----V----\|
- ||Server|<---------------->| User ||
- || PI || FTP Replies || PI ||
- |\--^---/| |\----^----/|
- | | | | | |
- -------- |/--V---\| Data |/----V----\| --------
- | File |<--->|Server|<---------------->| User |<--->| File |
- |System| || DTP || Connection || DTP || |System|
- -------- |\------/| |\---------/| --------
- ---------- -------------
-
- Server-FTP USER-FTP
-
- NOTES: 1. The data connection may be used in either direction.
- 2. The data connection need not exist all of the time.
-
- Figure 1 Model for FTP Use
-
- In the model described in Figure 1, the user-protocol interpreter
- initiates the control connection. The control connection follows
- the Telnet protocol. At the initiation of the user, standard FTP
- commands are generated by the user-PI and transmitted to the
- server process via the control connection. (The user may
- establish a direct control connection to the server-FTP, from a
- TAC terminal for example, and generate standard FTP commands
- independently, bypassing the user-FTP process.) Standard replies
- are sent from the server-PI to the user-PI over the control
- connection in response to the commands.
-
- The FTP commands specify the parameters for the data connection
- (data port, transfer mode, representation type, and structure) and
- the nature of file system operation (store, retrieve, append,
- delete, etc.). The user-DTP or its designate should "listen" on
- the specified data port, and the server initiate the data
- connection and data transfer in accordance with the specified
- parameters. It should be noted that the data port need not be in
-
-
-Postel & Reynolds [Page 8]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- the same host that initiates the FTP commands via the control
- connection, but the user or the user-FTP process must ensure a
- "listen" on the specified data port. It ought to also be noted
- that the data connection may be used for simultaneous sending and
- receiving.
-
- In another situation a user might wish to transfer files between
- two hosts, neither of which is a local host. The user sets up
- control connections to the two servers and then arranges for a
- data connection between them. In this manner, control information
- is passed to the user-PI but data is transferred between the
- server data transfer processes. Following is a model of this
- server-server interaction.
-
-
- Control ------------ Control
- ---------->| User-FTP |<-----------
- | | User-PI | |
- | | "C" | |
- V ------------ V
- -------------- --------------
- | Server-FTP | Data Connection | Server-FTP |
- | "A" |<---------------------->| "B" |
- -------------- Port (A) Port (B) --------------
-
-
- Figure 2
-
- The protocol requires that the control connections be open while
- data transfer is in progress. It is the responsibility of the
- user to request the closing of the control connections when
- finished using the FTP service, while it is the server who takes
- the action. The server may abort data transfer if the control
- connections are closed without command.
-
- The Relationship between FTP and Telnet:
-
- The FTP uses the Telnet protocol on the control connection.
- This can be achieved in two ways: first, the user-PI or the
- server-PI may implement the rules of the Telnet Protocol
- directly in their own procedures; or, second, the user-PI or
- the server-PI may make use of the existing Telnet module in the
- system.
-
- Ease of implementaion, sharing code, and modular programming
- argue for the second approach. Efficiency and independence
-
-
-
-Postel & Reynolds [Page 9]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- argue for the first approach. In practice, FTP relies on very
- little of the Telnet Protocol, so the first approach does not
- necessarily involve a large amount of code.
-
-3. DATA TRANSFER FUNCTIONS
-
- Files are transferred only via the data connection. The control
- connection is used for the transfer of commands, which describe the
- functions to be performed, and the replies to these commands (see the
- Section on FTP Replies). Several commands are concerned with the
- transfer of data between hosts. These data transfer commands include
- the MODE command which specify how the bits of the data are to be
- transmitted, and the STRUcture and TYPE commands, which are used to
- define the way in which the data are to be represented. The
- transmission and representation are basically independent but the
- "Stream" transmission mode is dependent on the file structure
- attribute and if "Compressed" transmission mode is used, the nature
- of the filler byte depends on the representation type.
-
- 3.1. DATA REPRESENTATION AND STORAGE
-
- Data is transferred from a storage device in the sending host to a
- storage device in the receiving host. Often it is necessary to
- perform certain transformations on the data because data storage
- representations in the two systems are different. For example,
- NVT-ASCII has different data storage representations in different
- systems. DEC TOPS-20s's generally store NVT-ASCII as five 7-bit
- ASCII characters, left-justified in a 36-bit word. IBM Mainframe's
- store NVT-ASCII as 8-bit EBCDIC codes. Multics stores NVT-ASCII
- as four 9-bit characters in a 36-bit word. It is desirable to
- convert characters into the standard NVT-ASCII representation when
- transmitting text between dissimilar systems. The sending and
- receiving sites would have to perform the necessary
- transformations between the standard representation and their
- internal representations.
-
- A different problem in representation arises when transmitting
- binary data (not character codes) between host systems with
- different word lengths. It is not always clear how the sender
- should send data, and the receiver store it. For example, when
- transmitting 32-bit bytes from a 32-bit word-length system to a
- 36-bit word-length system, it may be desirable (for reasons of
- efficiency and usefulness) to store the 32-bit bytes
- right-justified in a 36-bit word in the latter system. In any
- case, the user should have the option of specifying data
- representation and transformation functions. It should be noted
-
-
-
-Postel & Reynolds [Page 10]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- that FTP provides for very limited data type representations.
- Transformations desired beyond this limited capability should be
- performed by the user directly.
-
- 3.1.1. DATA TYPES
-
- Data representations are handled in FTP by a user specifying a
- representation type. This type may implicitly (as in ASCII or
- EBCDIC) or explicitly (as in Local byte) define a byte size for
- interpretation which is referred to as the "logical byte size."
- Note that this has nothing to do with the byte size used for
- transmission over the data connection, called the "transfer
- byte size", and the two should not be confused. For example,
- NVT-ASCII has a logical byte size of 8 bits. If the type is
- Local byte, then the TYPE command has an obligatory second
- parameter specifying the logical byte size. The transfer byte
- size is always 8 bits.
-
- 3.1.1.1. ASCII TYPE
-
- This is the default type and must be accepted by all FTP
- implementations. It is intended primarily for the transfer
- of text files, except when both hosts would find the EBCDIC
- type more convenient.
-
- The sender converts the data from an internal character
- representation to the standard 8-bit NVT-ASCII
- representation (see the Telnet specification). The receiver
- will convert the data from the standard form to his own
- internal form.
-
- In accordance with the NVT standard, the <CRLF> sequence
- should be used where necessary to denote the end of a line
- of text. (See the discussion of file structure at the end
- of the Section on Data Representation and Storage.)
-
- Using the standard NVT-ASCII representation means that data
- must be interpreted as 8-bit bytes.
-
- The Format parameter for ASCII and EBCDIC types is discussed
- below.
-
-
-
-
-
-
-
-
-Postel & Reynolds [Page 11]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- 3.1.1.2. EBCDIC TYPE
-
- This type is intended for efficient transfer between hosts
- which use EBCDIC for their internal character
- representation.
-
- For transmission, the data are represented as 8-bit EBCDIC
- characters. The character code is the only difference
- between the functional specifications of EBCDIC and ASCII
- types.
-
- End-of-line (as opposed to end-of-record--see the discussion
- of structure) will probably be rarely used with EBCDIC type
- for purposes of denoting structure, but where it is
- necessary the <NL> character should be used.
-
- 3.1.1.3. IMAGE TYPE
-
- The data are sent as contiguous bits which, for transfer,
- are packed into the 8-bit transfer bytes. The receiving
- site must store the data as contiguous bits. The structure
- of the storage system might necessitate the padding of the
- file (or of each record, for a record-structured file) to
- some convenient boundary (byte, word or block). This
- padding, which must be all zeros, may occur only at the end
- of the file (or at the end of each record) and there must be
- a way of identifying the padding bits so that they may be
- stripped off if the file is retrieved. The padding
- transformation should be well publicized to enable a user to
- process a file at the storage site.
-
- Image type is intended for the efficient storage and
- retrieval of files and for the transfer of binary data. It
- is recommended that this type be accepted by all FTP
- implementations.
-
- 3.1.1.4. LOCAL TYPE
-
- The data is transferred in logical bytes of the size
- specified by the obligatory second parameter, Byte size.
- The value of Byte size must be a decimal integer; there is
- no default value. The logical byte size is not necessarily
- the same as the transfer byte size. If there is a
- difference in byte sizes, then the logical bytes should be
- packed contiguously, disregarding transfer byte boundaries
- and with any necessary padding at the end.
-
-
-
-Postel & Reynolds [Page 12]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- When the data reaches the receiving host, it will be
- transformed in a manner dependent on the logical byte size
- and the particular host. This transformation must be
- invertible (i.e., an identical file can be retrieved if the
- same parameters are used) and should be well publicized by
- the FTP implementors.
-
- For example, a user sending 36-bit floating-point numbers to
- a host with a 32-bit word could send that data as Local byte
- with a logical byte size of 36. The receiving host would
- then be expected to store the logical bytes so that they
- could be easily manipulated; in this example putting the
- 36-bit logical bytes into 64-bit double words should
- suffice.
-
- In another example, a pair of hosts with a 36-bit word size
- may send data to one another in words by using TYPE L 36.
- The data would be sent in the 8-bit transmission bytes
- packed so that 9 transmission bytes carried two host words.
-
- 3.1.1.5. FORMAT CONTROL
-
- The types ASCII and EBCDIC also take a second (optional)
- parameter; this is to indicate what kind of vertical format
- control, if any, is associated with a file. The following
- data representation types are defined in FTP:
-
- A character file may be transferred to a host for one of
- three purposes: for printing, for storage and later
- retrieval, or for processing. If a file is sent for
- printing, the receiving host must know how the vertical
- format control is represented. In the second case, it must
- be possible to store a file at a host and then retrieve it
- later in exactly the same form. Finally, it should be
- possible to move a file from one host to another and process
- the file at the second host without undue trouble. A single
- ASCII or EBCDIC format does not satisfy all these
- conditions. Therefore, these types have a second parameter
- specifying one of the following three formats:
-
- 3.1.1.5.1. NON PRINT
-
- This is the default format to be used if the second
- (format) parameter is omitted. Non-print format must be
- accepted by all FTP implementations.
-
-
-
-
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-
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-
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-File Transfer Protocol
-
-
- The file need contain no vertical format information. If
- it is passed to a printer process, this process may
- assume standard values for spacing and margins.
-
- Normally, this format will be used with files destined
- for processing or just storage.
-
- 3.1.1.5.2. TELNET FORMAT CONTROLS
-
- The file contains ASCII/EBCDIC vertical format controls
- (i.e., <CR>, <LF>, <NL>, <VT>, <FF>) which the printer
- process will interpret appropriately. <CRLF>, in exactly
- this sequence, also denotes end-of-line.
-
- 3.1.1.5.2. CARRIAGE CONTROL (ASA)
-
- The file contains ASA (FORTRAN) vertical format control
- characters. (See RFC 740 Appendix C; and Communications
- of the ACM, Vol. 7, No. 10, p. 606, October 1964.) In a
- line or a record formatted according to the ASA Standard,
- the first character is not to be printed. Instead, it
- should be used to determine the vertical movement of the
- paper which should take place before the rest of the
- record is printed.
-
- The ASA Standard specifies the following control
- characters:
-
- Character Vertical Spacing
-
- blank Move paper up one line
- 0 Move paper up two lines
- 1 Move paper to top of next page
- + No movement, i.e., overprint
-
- Clearly there must be some way for a printer process to
- distinguish the end of the structural entity. If a file
- has record structure (see below) this is no problem;
- records will be explicitly marked during transfer and
- storage. If the file has no record structure, the <CRLF>
- end-of-line sequence is used to separate printing lines,
- but these format effectors are overridden by the ASA
- controls.
-
-
-
-
-
-
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-
-
- 3.1.2. DATA STRUCTURES
-
- In addition to different representation types, FTP allows the
- structure of a file to be specified. Three file structures are
- defined in FTP:
-
- file-structure, where there is no internal structure and
- the file is considered to be a
- continuous sequence of data bytes,
-
- record-structure, where the file is made up of sequential
- records,
-
- and page-structure, where the file is made up of independent
- indexed pages.
-
- File-structure is the default to be assumed if the STRUcture
- command has not been used but both file and record structures
- must be accepted for "text" files (i.e., files with TYPE ASCII
- or EBCDIC) by all FTP implementations. The structure of a file
- will affect both the transfer mode of a file (see the Section
- on Transmission Modes) and the interpretation and storage of
- the file.
-
- The "natural" structure of a file will depend on which host
- stores the file. A source-code file will usually be stored on
- an IBM Mainframe in fixed length records but on a DEC TOPS-20
- as a stream of characters partitioned into lines, for example
- by <CRLF>. If the transfer of files between such disparate
- sites is to be useful, there must be some way for one site to
- recognize the other's assumptions about the file.
-
- With some sites being naturally file-oriented and others
- naturally record-oriented there may be problems if a file with
- one structure is sent to a host oriented to the other. If a
- text file is sent with record-structure to a host which is file
- oriented, then that host should apply an internal
- transformation to the file based on the record structure.
- Obviously, this transformation should be useful, but it must
- also be invertible so that an identical file may be retrieved
- using record structure.
-
- In the case of a file being sent with file-structure to a
- record-oriented host, there exists the question of what
- criteria the host should use to divide the file into records
- which can be processed locally. If this division is necessary,
- the FTP implementation should use the end-of-line sequence,
-
-
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-
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-RFC 959 October 1985
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-
-
- <CRLF> for ASCII, or <NL> for EBCDIC text files, as the
- delimiter. If an FTP implementation adopts this technique, it
- must be prepared to reverse the transformation if the file is
- retrieved with file-structure.
-
- 3.1.2.1. FILE STRUCTURE
-
- File structure is the default to be assumed if the STRUcture
- command has not been used.
-
- In file-structure there is no internal structure and the
- file is considered to be a continuous sequence of data
- bytes.
-
- 3.1.2.2. RECORD STRUCTURE
-
- Record structures must be accepted for "text" files (i.e.,
- files with TYPE ASCII or EBCDIC) by all FTP implementations.
-
- In record-structure the file is made up of sequential
- records.
-
- 3.1.2.3. PAGE STRUCTURE
-
- To transmit files that are discontinuous, FTP defines a page
- structure. Files of this type are sometimes known as
- "random access files" or even as "holey files". In these
- files there is sometimes other information associated with
- the file as a whole (e.g., a file descriptor), or with a
- section of the file (e.g., page access controls), or both.
- In FTP, the sections of the file are called pages.
-
- To provide for various page sizes and associated
- information, each page is sent with a page header. The page
- header has the following defined fields:
-
- Header Length
-
- The number of logical bytes in the page header
- including this byte. The minimum header length is 4.
-
- Page Index
-
- The logical page number of this section of the file.
- This is not the transmission sequence number of this
- page, but the index used to identify this page of the
- file.
-
-
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-
-
- Data Length
-
- The number of logical bytes in the page data. The
- minimum data length is 0.
-
- Page Type
-
- The type of page this is. The following page types
- are defined:
-
- 0 = Last Page
-
- This is used to indicate the end of a paged
- structured transmission. The header length must
- be 4, and the data length must be 0.
-
- 1 = Simple Page
-
- This is the normal type for simple paged files
- with no page level associated control
- information. The header length must be 4.
-
- 2 = Descriptor Page
-
- This type is used to transmit the descriptive
- information for the file as a whole.
-
- 3 = Access Controlled Page
-
- This type includes an additional header field
- for paged files with page level access control
- information. The header length must be 5.
-
- Optional Fields
-
- Further header fields may be used to supply per page
- control information, for example, per page access
- control.
-
- All fields are one logical byte in length. The logical byte
- size is specified by the TYPE command. See Appendix I for
- further details and a specific case at the page structure.
-
- A note of caution about parameters: a file must be stored and
- retrieved with the same parameters if the retrieved version is to
-
-
-
-
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-
-
- be identical to the version originally transmitted. Conversely,
- FTP implementations must return a file identical to the original
- if the parameters used to store and retrieve a file are the same.
-
- 3.2. ESTABLISHING DATA CONNECTIONS
-
- The mechanics of transferring data consists of setting up the data
- connection to the appropriate ports and choosing the parameters
- for transfer. Both the user and the server-DTPs have a default
- data port. The user-process default data port is the same as the
- control connection port (i.e., U). The server-process default
- data port is the port adjacent to the control connection port
- (i.e., L-1).
-
- The transfer byte size is 8-bit bytes. This byte size is relevant
- only for the actual transfer of the data; it has no bearing on
- representation of the data within a host's file system.
-
- The passive data transfer process (this may be a user-DTP or a
- second server-DTP) shall "listen" on the data port prior to
- sending a transfer request command. The FTP request command
- determines the direction of the data transfer. The server, upon
- receiving the transfer request, will initiate the data connection
- to the port. When the connection is established, the data
- transfer begins between DTP's, and the server-PI sends a
- confirming reply to the user-PI.
-
- Every FTP implementation must support the use of the default data
- ports, and only the USER-PI can initiate a change to non-default
- ports.
-
- It is possible for the user to specify an alternate data port by
- use of the PORT command. The user may want a file dumped on a TAC
- line printer or retrieved from a third party host. In the latter
- case, the user-PI sets up control connections with both
- server-PI's. One server is then told (by an FTP command) to
- "listen" for a connection which the other will initiate. The
- user-PI sends one server-PI a PORT command indicating the data
- port of the other. Finally, both are sent the appropriate
- transfer commands. The exact sequence of commands and replies
- sent between the user-controller and the servers is defined in the
- Section on FTP Replies.
-
- In general, it is the server's responsibility to maintain the data
- connection--to initiate it and to close it. The exception to this
-
-
-
-
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-
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-
-
- is when the user-DTP is sending the data in a transfer mode that
- requires the connection to be closed to indicate EOF. The server
- MUST close the data connection under the following conditions:
-
- 1. The server has completed sending data in a transfer mode
- that requires a close to indicate EOF.
-
- 2. The server receives an ABORT command from the user.
-
- 3. The port specification is changed by a command from the
- user.
-
- 4. The control connection is closed legally or otherwise.
-
- 5. An irrecoverable error condition occurs.
-
- Otherwise the close is a server option, the exercise of which the
- server must indicate to the user-process by either a 250 or 226
- reply only.
-
- 3.3. DATA CONNECTION MANAGEMENT
-
- Default Data Connection Ports: All FTP implementations must
- support use of the default data connection ports, and only the
- User-PI may initiate the use of non-default ports.
-
- Negotiating Non-Default Data Ports: The User-PI may specify a
- non-default user side data port with the PORT command. The
- User-PI may request the server side to identify a non-default
- server side data port with the PASV command. Since a connection
- is defined by the pair of addresses, either of these actions is
- enough to get a different data connection, still it is permitted
- to do both commands to use new ports on both ends of the data
- connection.
-
- Reuse of the Data Connection: When using the stream mode of data
- transfer the end of the file must be indicated by closing the
- connection. This causes a problem if multiple files are to be
- transfered in the session, due to need for TCP to hold the
- connection record for a time out period to guarantee the reliable
- communication. Thus the connection can not be reopened at once.
-
- There are two solutions to this problem. The first is to
- negotiate a non-default port. The second is to use another
- transfer mode.
-
- A comment on transfer modes. The stream transfer mode is
-
-
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-
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-
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-
-
- inherently unreliable, since one can not determine if the
- connection closed prematurely or not. The other transfer modes
- (Block, Compressed) do not close the connection to indicate the
- end of file. They have enough FTP encoding that the data
- connection can be parsed to determine the end of the file.
- Thus using these modes one can leave the data connection open
- for multiple file transfers.
-
- 3.4. TRANSMISSION MODES
-
- The next consideration in transferring data is choosing the
- appropriate transmission mode. There are three modes: one which
- formats the data and allows for restart procedures; one which also
- compresses the data for efficient transfer; and one which passes
- the data with little or no processing. In this last case the mode
- interacts with the structure attribute to determine the type of
- processing. In the compressed mode, the representation type
- determines the filler byte.
-
- All data transfers must be completed with an end-of-file (EOF)
- which may be explicitly stated or implied by the closing of the
- data connection. For files with record structure, all the
- end-of-record markers (EOR) are explicit, including the final one.
- For files transmitted in page structure a "last-page" page type is
- used.
-
- NOTE: In the rest of this section, byte means "transfer byte"
- except where explicitly stated otherwise.
-
- For the purpose of standardized transfer, the sending host will
- translate its internal end of line or end of record denotation
- into the representation prescribed by the transfer mode and file
- structure, and the receiving host will perform the inverse
- translation to its internal denotation. An IBM Mainframe record
- count field may not be recognized at another host, so the
- end-of-record information may be transferred as a two byte control
- code in Stream mode or as a flagged bit in a Block or Compressed
- mode descriptor. End-of-line in an ASCII or EBCDIC file with no
- record structure should be indicated by <CRLF> or <NL>,
- respectively. Since these transformations imply extra work for
- some systems, identical systems transferring non-record structured
- text files might wish to use a binary representation and stream
- mode for the transfer.
-
-
-
-
-
-
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-
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-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- The following transmission modes are defined in FTP:
-
- 3.4.1. STREAM MODE
-
- The data is transmitted as a stream of bytes. There is no
- restriction on the representation type used; record structures
- are allowed.
-
- In a record structured file EOR and EOF will each be indicated
- by a two-byte control code. The first byte of the control code
- will be all ones, the escape character. The second byte will
- have the low order bit on and zeros elsewhere for EOR and the
- second low order bit on for EOF; that is, the byte will have
- value 1 for EOR and value 2 for EOF. EOR and EOF may be
- indicated together on the last byte transmitted by turning both
- low order bits on (i.e., the value 3). If a byte of all ones
- was intended to be sent as data, it should be repeated in the
- second byte of the control code.
-
- If the structure is a file structure, the EOF is indicated by
- the sending host closing the data connection and all bytes are
- data bytes.
-
- 3.4.2. BLOCK MODE
-
- The file is transmitted as a series of data blocks preceded by
- one or more header bytes. The header bytes contain a count
- field, and descriptor code. The count field indicates the
- total length of the data block in bytes, thus marking the
- beginning of the next data block (there are no filler bits).
- The descriptor code defines: last block in the file (EOF) last
- block in the record (EOR), restart marker (see the Section on
- Error Recovery and Restart) or suspect data (i.e., the data
- being transferred is suspected of errors and is not reliable).
- This last code is NOT intended for error control within FTP.
- It is motivated by the desire of sites exchanging certain types
- of data (e.g., seismic or weather data) to send and receive all
- the data despite local errors (such as "magnetic tape read
- errors"), but to indicate in the transmission that certain
- portions are suspect). Record structures are allowed in this
- mode, and any representation type may be used.
-
- The header consists of the three bytes. Of the 24 bits of
- header information, the 16 low order bits shall represent byte
- count, and the 8 high order bits shall represent descriptor
- codes as shown below.
-
-
-
-Postel & Reynolds [Page 21]
-
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-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- Block Header
-
- +----------------+----------------+----------------+
- | Descriptor | Byte Count |
- | 8 bits | 16 bits |
- +----------------+----------------+----------------+
-
-
- The descriptor codes are indicated by bit flags in the
- descriptor byte. Four codes have been assigned, where each
- code number is the decimal value of the corresponding bit in
- the byte.
-
- Code Meaning
-
- 128 End of data block is EOR
- 64 End of data block is EOF
- 32 Suspected errors in data block
- 16 Data block is a restart marker
-
- With this encoding, more than one descriptor coded condition
- may exist for a particular block. As many bits as necessary
- may be flagged.
-
- The restart marker is embedded in the data stream as an
- integral number of 8-bit bytes representing printable
- characters in the language being used over the control
- connection (e.g., default--NVT-ASCII). <SP> (Space, in the
- appropriate language) must not be used WITHIN a restart marker.
-
- For example, to transmit a six-character marker, the following
- would be sent:
-
- +--------+--------+--------+
- |Descrptr| Byte count |
- |code= 16| = 6 |
- +--------+--------+--------+
-
- +--------+--------+--------+
- | Marker | Marker | Marker |
- | 8 bits | 8 bits | 8 bits |
- +--------+--------+--------+
-
- +--------+--------+--------+
- | Marker | Marker | Marker |
- | 8 bits | 8 bits | 8 bits |
- +--------+--------+--------+
-
-
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-
-RFC 959 October 1985
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-
-
- 3.4.3. COMPRESSED MODE
-
- There are three kinds of information to be sent: regular data,
- sent in a byte string; compressed data, consisting of
- replications or filler; and control information, sent in a
- two-byte escape sequence. If n>0 bytes (up to 127) of regular
- data are sent, these n bytes are preceded by a byte with the
- left-most bit set to 0 and the right-most 7 bits containing the
- number n.
-
- Byte string:
-
- 1 7 8 8
- +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
- |0| n | | d(1) | ... | d(n) |
- +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
- ^ ^
- |---n bytes---|
- of data
-
- String of n data bytes d(1),..., d(n)
- Count n must be positive.
-
- To compress a string of n replications of the data byte d, the
- following 2 bytes are sent:
-
- Replicated Byte:
-
- 2 6 8
- +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
- |1 0| n | | d |
- +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
-
- A string of n filler bytes can be compressed into a single
- byte, where the filler byte varies with the representation
- type. If the type is ASCII or EBCDIC the filler byte is <SP>
- (Space, ASCII code 32, EBCDIC code 64). If the type is Image
- or Local byte the filler is a zero byte.
-
- Filler String:
-
- 2 6
- +-+-+-+-+-+-+-+-+
- |1 1| n |
- +-+-+-+-+-+-+-+-+
-
- The escape sequence is a double byte, the first of which is the
-
-
-Postel & Reynolds [Page 23]
-
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-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- escape byte (all zeros) and the second of which contains
- descriptor codes as defined in Block mode. The descriptor
- codes have the same meaning as in Block mode and apply to the
- succeeding string of bytes.
-
- Compressed mode is useful for obtaining increased bandwidth on
- very large network transmissions at a little extra CPU cost.
- It can be most effectively used to reduce the size of printer
- files such as those generated by RJE hosts.
-
- 3.5. ERROR RECOVERY AND RESTART
-
- There is no provision for detecting bits lost or scrambled in data
- transfer; this level of error control is handled by the TCP.
- However, a restart procedure is provided to protect users from
- gross system failures (including failures of a host, an
- FTP-process, or the underlying network).
-
- The restart procedure is defined only for the block and compressed
- modes of data transfer. It requires the sender of data to insert
- a special marker code in the data stream with some marker
- information. The marker information has meaning only to the
- sender, but must consist of printable characters in the default or
- negotiated language of the control connection (ASCII or EBCDIC).
- The marker could represent a bit-count, a record-count, or any
- other information by which a system may identify a data
- checkpoint. The receiver of data, if it implements the restart
- procedure, would then mark the corresponding position of this
- marker in the receiving system, and return this information to the
- user.
-
- In the event of a system failure, the user can restart the data
- transfer by identifying the marker point with the FTP restart
- procedure. The following example illustrates the use of the
- restart procedure.
-
- The sender of the data inserts an appropriate marker block in the
- data stream at a convenient point. The receiving host marks the
- corresponding data point in its file system and conveys the last
- known sender and receiver marker information to the user, either
- directly or over the control connection in a 110 reply (depending
- on who is the sender). In the event of a system failure, the user
- or controller process restarts the server at the last server
- marker by sending a restart command with server's marker code as
- its argument. The restart command is transmitted over the control
-
-
-
-
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-
-RFC 959 October 1985
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-
-
- connection and is immediately followed by the command (such as
- RETR, STOR or LIST) which was being executed when the system
- failure occurred.
-
-4. FILE TRANSFER FUNCTIONS
-
- The communication channel from the user-PI to the server-PI is
- established as a TCP connection from the user to the standard server
- port. The user protocol interpreter is responsible for sending FTP
- commands and interpreting the replies received; the server-PI
- interprets commands, sends replies and directs its DTP to set up the
- data connection and transfer the data. If the second party to the
- data transfer (the passive transfer process) is the user-DTP, then it
- is governed through the internal protocol of the user-FTP host; if it
- is a second server-DTP, then it is governed by its PI on command from
- the user-PI. The FTP replies are discussed in the next section. In
- the description of a few of the commands in this section, it is
- helpful to be explicit about the possible replies.
-
- 4.1. FTP COMMANDS
-
- 4.1.1. ACCESS CONTROL COMMANDS
-
- The following commands specify access control identifiers
- (command codes are shown in parentheses).
-
- USER NAME (USER)
-
- The argument field is a Telnet string identifying the user.
- The user identification is that which is required by the
- server for access to its file system. This command will
- normally be the first command transmitted by the user after
- the control connections are made (some servers may require
- this). Additional identification information in the form of
- a password and/or an account command may also be required by
- some servers. Servers may allow a new USER command to be
- entered at any point in order to change the access control
- and/or accounting information. This has the effect of
- flushing any user, password, and account information already
- supplied and beginning the login sequence again. All
- transfer parameters are unchanged and any file transfer in
- progress is completed under the old access control
- parameters.
-
-
-
-
-
-
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-
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-
-
- PASSWORD (PASS)
-
- The argument field is a Telnet string specifying the user's
- password. This command must be immediately preceded by the
- user name command, and, for some sites, completes the user's
- identification for access control. Since password
- information is quite sensitive, it is desirable in general
- to "mask" it or suppress typeout. It appears that the
- server has no foolproof way to achieve this. It is
- therefore the responsibility of the user-FTP process to hide
- the sensitive password information.
-
- ACCOUNT (ACCT)
-
- The argument field is a Telnet string identifying the user's
- account. The command is not necessarily related to the USER
- command, as some sites may require an account for login and
- others only for specific access, such as storing files. In
- the latter case the command may arrive at any time.
-
- There are reply codes to differentiate these cases for the
- automation: when account information is required for login,
- the response to a successful PASSword command is reply code
- 332. On the other hand, if account information is NOT
- required for login, the reply to a successful PASSword
- command is 230; and if the account information is needed for
- a command issued later in the dialogue, the server should
- return a 332 or 532 reply depending on whether it stores
- (pending receipt of the ACCounT command) or discards the
- command, respectively.
-
- CHANGE WORKING DIRECTORY (CWD)
-
- This command allows the user to work with a different
- directory or dataset for file storage or retrieval without
- altering his login or accounting information. Transfer
- parameters are similarly unchanged. The argument is a
- pathname specifying a directory or other system dependent
- file group designator.
-
- CHANGE TO PARENT DIRECTORY (CDUP)
-
- This command is a special case of CWD, and is included to
- simplify the implementation of programs for transferring
- directory trees between operating systems having different
-
-
-
-
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-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- syntaxes for naming the parent directory. The reply codes
- shall be identical to the reply codes of CWD. See
- Appendix II for further details.
-
- STRUCTURE MOUNT (SMNT)
-
- This command allows the user to mount a different file
- system data structure without altering his login or
- accounting information. Transfer parameters are similarly
- unchanged. The argument is a pathname specifying a
- directory or other system dependent file group designator.
-
- REINITIALIZE (REIN)
-
- This command terminates a USER, flushing all I/O and account
- information, except to allow any transfer in progress to be
- completed. All parameters are reset to the default settings
- and the control connection is left open. This is identical
- to the state in which a user finds himself immediately after
- the control connection is opened. A USER command may be
- expected to follow.
-
- LOGOUT (QUIT)
-
- This command terminates a USER and if file transfer is not
- in progress, the server closes the control connection. If
- file transfer is in progress, the connection will remain
- open for result response and the server will then close it.
- If the user-process is transferring files for several USERs
- but does not wish to close and then reopen connections for
- each, then the REIN command should be used instead of QUIT.
-
- An unexpected close on the control connection will cause the
- server to take the effective action of an abort (ABOR) and a
- logout (QUIT).
-
- 4.1.2. TRANSFER PARAMETER COMMANDS
-
- All data transfer parameters have default values, and the
- commands specifying data transfer parameters are required only
- if the default parameter values are to be changed. The default
- value is the last specified value, or if no value has been
- specified, the standard default value is as stated here. This
- implies that the server must "remember" the applicable default
- values. The commands may be in any order except that they must
- precede the FTP service request. The following commands
- specify data transfer parameters:
-
-
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-
-
- DATA PORT (PORT)
-
- The argument is a HOST-PORT specification for the data port
- to be used in data connection. There are defaults for both
- the user and server data ports, and under normal
- circumstances this command and its reply are not needed. If
- this command is used, the argument is the concatenation of a
- 32-bit internet host address and a 16-bit TCP port address.
- This address information is broken into 8-bit fields and the
- value of each field is transmitted as a decimal number (in
- character string representation). The fields are separated
- by commas. A port command would be:
-
- PORT h1,h2,h3,h4,p1,p2
-
- where h1 is the high order 8 bits of the internet host
- address.
-
- PASSIVE (PASV)
-
- This command requests the server-DTP to "listen" on a data
- port (which is not its default data port) and to wait for a
- connection rather than initiate one upon receipt of a
- transfer command. The response to this command includes the
- host and port address this server is listening on.
-
- REPRESENTATION TYPE (TYPE)
-
- The argument specifies the representation type as described
- in the Section on Data Representation and Storage. Several
- types take a second parameter. The first parameter is
- denoted by a single Telnet character, as is the second
- Format parameter for ASCII and EBCDIC; the second parameter
- for local byte is a decimal integer to indicate Bytesize.
- The parameters are separated by a <SP> (Space, ASCII code
- 32).
-
- The following codes are assigned for type:
-
- \ /
- A - ASCII | | N - Non-print
- |-><-| T - Telnet format effectors
- E - EBCDIC| | C - Carriage Control (ASA)
- / \
- I - Image
-
- L <byte size> - Local byte Byte size
-
-
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-
-
- The default representation type is ASCII Non-print. If the
- Format parameter is changed, and later just the first
- argument is changed, Format then returns to the Non-print
- default.
-
- FILE STRUCTURE (STRU)
-
- The argument is a single Telnet character code specifying
- file structure described in the Section on Data
- Representation and Storage.
-
- The following codes are assigned for structure:
-
- F - File (no record structure)
- R - Record structure
- P - Page structure
-
- The default structure is File.
-
- TRANSFER MODE (MODE)
-
- The argument is a single Telnet character code specifying
- the data transfer modes described in the Section on
- Transmission Modes.
-
- The following codes are assigned for transfer modes:
-
- S - Stream
- B - Block
- C - Compressed
-
- The default transfer mode is Stream.
-
- 4.1.3. FTP SERVICE COMMANDS
-
- The FTP service commands define the file transfer or the file
- system function requested by the user. The argument of an FTP
- service command will normally be a pathname. The syntax of
- pathnames must conform to server site conventions (with
- standard defaults applicable), and the language conventions of
- the control connection. The suggested default handling is to
- use the last specified device, directory or file name, or the
- standard default defined for local users. The commands may be
- in any order except that a "rename from" command must be
- followed by a "rename to" command and the restart command must
- be followed by the interrupted service command (e.g., STOR or
- RETR). The data, when transferred in response to FTP service
-
-
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-
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-
-
- commands, shall always be sent over the data connection, except
- for certain informative replies. The following commands
- specify FTP service requests:
-
- RETRIEVE (RETR)
-
- This command causes the server-DTP to transfer a copy of the
- file, specified in the pathname, to the server- or user-DTP
- at the other end of the data connection. The status and
- contents of the file at the server site shall be unaffected.
-
- STORE (STOR)
-
- This command causes the server-DTP to accept the data
- transferred via the data connection and to store the data as
- a file at the server site. If the file specified in the
- pathname exists at the server site, then its contents shall
- be replaced by the data being transferred. A new file is
- created at the server site if the file specified in the
- pathname does not already exist.
-
- STORE UNIQUE (STOU)
-
- This command behaves like STOR except that the resultant
- file is to be created in the current directory under a name
- unique to that directory. The 250 Transfer Started response
- must include the name generated.
-
- APPEND (with create) (APPE)
-
- This command causes the server-DTP to accept the data
- transferred via the data connection and to store the data in
- a file at the server site. If the file specified in the
- pathname exists at the server site, then the data shall be
- appended to that file; otherwise the file specified in the
- pathname shall be created at the server site.
-
- ALLOCATE (ALLO)
-
- This command may be required by some servers to reserve
- sufficient storage to accommodate the new file to be
- transferred. The argument shall be a decimal integer
- representing the number of bytes (using the logical byte
- size) of storage to be reserved for the file. For files
- sent with record or page structure a maximum record or page
- size (in logical bytes) might also be necessary; this is
- indicated by a decimal integer in a second argument field of
-
-
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-
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-
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-
-
- the command. This second argument is optional, but when
- present should be separated from the first by the three
- Telnet characters <SP> R <SP>. This command shall be
- followed by a STORe or APPEnd command. The ALLO command
- should be treated as a NOOP (no operation) by those servers
- which do not require that the maximum size of the file be
- declared beforehand, and those servers interested in only
- the maximum record or page size should accept a dummy value
- in the first argument and ignore it.
-
- RESTART (REST)
-
- The argument field represents the server marker at which
- file transfer is to be restarted. This command does not
- cause file transfer but skips over the file to the specified
- data checkpoint. This command shall be immediately followed
- by the appropriate FTP service command which shall cause
- file transfer to resume.
-
- RENAME FROM (RNFR)
-
- This command specifies the old pathname of the file which is
- to be renamed. This command must be immediately followed by
- a "rename to" command specifying the new file pathname.
-
- RENAME TO (RNTO)
-
- This command specifies the new pathname of the file
- specified in the immediately preceding "rename from"
- command. Together the two commands cause a file to be
- renamed.
-
- ABORT (ABOR)
-
- This command tells the server to abort the previous FTP
- service command and any associated transfer of data. The
- abort command may require "special action", as discussed in
- the Section on FTP Commands, to force recognition by the
- server. No action is to be taken if the previous command
- has been completed (including data transfer). The control
- connection is not to be closed by the server, but the data
- connection must be closed.
-
- There are two cases for the server upon receipt of this
- command: (1) the FTP service command was already completed,
- or (2) the FTP service command is still in progress.
-
-
-
-Postel & Reynolds [Page 31]
-
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-File Transfer Protocol
-
-
- In the first case, the server closes the data connection
- (if it is open) and responds with a 226 reply, indicating
- that the abort command was successfully processed.
-
- In the second case, the server aborts the FTP service in
- progress and closes the data connection, returning a 426
- reply to indicate that the service request terminated
- abnormally. The server then sends a 226 reply,
- indicating that the abort command was successfully
- processed.
-
- DELETE (DELE)
-
- This command causes the file specified in the pathname to be
- deleted at the server site. If an extra level of protection
- is desired (such as the query, "Do you really wish to
- delete?"), it should be provided by the user-FTP process.
-
- REMOVE DIRECTORY (RMD)
-
- This command causes the directory specified in the pathname
- to be removed as a directory (if the pathname is absolute)
- or as a subdirectory of the current working directory (if
- the pathname is relative). See Appendix II.
-
- MAKE DIRECTORY (MKD)
-
- This command causes the directory specified in the pathname
- to be created as a directory (if the pathname is absolute)
- or as a subdirectory of the current working directory (if
- the pathname is relative). See Appendix II.
-
- PRINT WORKING DIRECTORY (PWD)
-
- This command causes the name of the current working
- directory to be returned in the reply. See Appendix II.
-
- LIST (LIST)
-
- This command causes a list to be sent from the server to the
- passive DTP. If the pathname specifies a directory or other
- group of files, the server should transfer a list of files
- in the specified directory. If the pathname specifies a
- file then the server should send current information on the
- file. A null argument implies the user's current working or
- default directory. The data transfer is over the data
- connection in type ASCII or type EBCDIC. (The user must
-
-
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-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- ensure that the TYPE is appropriately ASCII or EBCDIC).
- Since the information on a file may vary widely from system
- to system, this information may be hard to use automatically
- in a program, but may be quite useful to a human user.
-
- NAME LIST (NLST)
-
- This command causes a directory listing to be sent from
- server to user site. The pathname should specify a
- directory or other system-specific file group descriptor; a
- null argument implies the current directory. The server
- will return a stream of names of files and no other
- information. The data will be transferred in ASCII or
- EBCDIC type over the data connection as valid pathname
- strings separated by <CRLF> or <NL>. (Again the user must
- ensure that the TYPE is correct.) This command is intended
- to return information that can be used by a program to
- further process the files automatically. For example, in
- the implementation of a "multiple get" function.
-
- SITE PARAMETERS (SITE)
-
- This command is used by the server to provide services
- specific to his system that are essential to file transfer
- but not sufficiently universal to be included as commands in
- the protocol. The nature of these services and the
- specification of their syntax can be stated in a reply to
- the HELP SITE command.
-
- SYSTEM (SYST)
-
- This command is used to find out the type of operating
- system at the server. The reply shall have as its first
- word one of the system names listed in the current version
- of the Assigned Numbers document [4].
-
- STATUS (STAT)
-
- This command shall cause a status response to be sent over
- the control connection in the form of a reply. The command
- may be sent during a file transfer (along with the Telnet IP
- and Synch signals--see the Section on FTP Commands) in which
- case the server will respond with the status of the
- operation in progress, or it may be sent between file
- transfers. In the latter case, the command may have an
- argument field. If the argument is a pathname, the command
- is analogous to the "list" command except that data shall be
-
-
-Postel & Reynolds [Page 33]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- transferred over the control connection. If a partial
- pathname is given, the server may respond with a list of
- file names or attributes associated with that specification.
- If no argument is given, the server should return general
- status information about the server FTP process. This
- should include current values of all transfer parameters and
- the status of connections.
-
- HELP (HELP)
-
- This command shall cause the server to send helpful
- information regarding its implementation status over the
- control connection to the user. The command may take an
- argument (e.g., any command name) and return more specific
- information as a response. The reply is type 211 or 214.
- It is suggested that HELP be allowed before entering a USER
- command. The server may use this reply to specify
- site-dependent parameters, e.g., in response to HELP SITE.
-
- NOOP (NOOP)
-
- This command does not affect any parameters or previously
- entered commands. It specifies no action other than that the
- server send an OK reply.
-
- The File Transfer Protocol follows the specifications of the Telnet
- protocol for all communications over the control connection. Since
- the language used for Telnet communication may be a negotiated
- option, all references in the next two sections will be to the
- "Telnet language" and the corresponding "Telnet end-of-line code".
- Currently, one may take these to mean NVT-ASCII and <CRLF>. No other
- specifications of the Telnet protocol will be cited.
-
- FTP commands are "Telnet strings" terminated by the "Telnet end of
- line code". The command codes themselves are alphabetic characters
- terminated by the character <SP> (Space) if parameters follow and
- Telnet-EOL otherwise. The command codes and the semantics of
- commands are described in this section; the detailed syntax of
- commands is specified in the Section on Commands, the reply sequences
- are discussed in the Section on Sequencing of Commands and Replies,
- and scenarios illustrating the use of commands are provided in the
- Section on Typical FTP Scenarios.
-
- FTP commands may be partitioned as those specifying access-control
- identifiers, data transfer parameters, or FTP service requests.
- Certain commands (such as ABOR, STAT, QUIT) may be sent over the
- control connection while a data transfer is in progress. Some
-
-
-Postel & Reynolds [Page 34]
-
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-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- servers may not be able to monitor the control and data connections
- simultaneously, in which case some special action will be necessary
- to get the server's attention. The following ordered format is
- tentatively recommended:
-
- 1. User system inserts the Telnet "Interrupt Process" (IP) signal
- in the Telnet stream.
-
- 2. User system sends the Telnet "Synch" signal.
-
- 3. User system inserts the command (e.g., ABOR) in the Telnet
- stream.
-
- 4. Server PI, after receiving "IP", scans the Telnet stream for
- EXACTLY ONE FTP command.
-
- (For other servers this may not be necessary but the actions listed
- above should have no unusual effect.)
-
- 4.2. FTP REPLIES
-
- Replies to File Transfer Protocol commands are devised to ensure
- the synchronization of requests and actions in the process of file
- transfer, and to guarantee that the user process always knows the
- state of the Server. Every command must generate at least one
- reply, although there may be more than one; in the latter case,
- the multiple replies must be easily distinguished. In addition,
- some commands occur in sequential groups, such as USER, PASS and
- ACCT, or RNFR and RNTO. The replies show the existence of an
- intermediate state if all preceding commands have been successful.
- A failure at any point in the sequence necessitates the repetition
- of the entire sequence from the beginning.
-
- The details of the command-reply sequence are made explicit in
- a set of state diagrams below.
-
- An FTP reply consists of a three digit number (transmitted as
- three alphanumeric characters) followed by some text. The number
- is intended for use by automata to determine what state to enter
- next; the text is intended for the human user. It is intended
- that the three digits contain enough encoded information that the
- user-process (the User-PI) will not need to examine the text and
- may either discard it or pass it on to the user, as appropriate.
- In particular, the text may be server-dependent, so there are
- likely to be varying texts for each reply code.
-
- A reply is defined to contain the 3-digit code, followed by Space
-
-
-Postel & Reynolds [Page 35]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- <SP>, followed by one line of text (where some maximum line length
- has been specified), and terminated by the Telnet end-of-line
- code. There will be cases however, where the text is longer than
- a single line. In these cases the complete text must be bracketed
- so the User-process knows when it may stop reading the reply (i.e.
- stop processing input on the control connection) and go do other
- things. This requires a special format on the first line to
- indicate that more than one line is coming, and another on the
- last line to designate it as the last. At least one of these must
- contain the appropriate reply code to indicate the state of the
- transaction. To satisfy all factions, it was decided that both
- the first and last line codes should be the same.
-
- Thus the format for multi-line replies is that the first line
- will begin with the exact required reply code, followed
- immediately by a Hyphen, "-" (also known as Minus), followed by
- text. The last line will begin with the same code, followed
- immediately by Space <SP>, optionally some text, and the Telnet
- end-of-line code.
-
- For example:
- 123-First line
- Second line
- 234 A line beginning with numbers
- 123 The last line
-
- The user-process then simply needs to search for the second
- occurrence of the same reply code, followed by <SP> (Space), at
- the beginning of a line, and ignore all intermediary lines. If
- an intermediary line begins with a 3-digit number, the Server
- must pad the front to avoid confusion.
-
- This scheme allows standard system routines to be used for
- reply information (such as for the STAT reply), with
- "artificial" first and last lines tacked on. In rare cases
- where these routines are able to generate three digits and a
- Space at the beginning of any line, the beginning of each
- text line should be offset by some neutral text, like Space.
-
- This scheme assumes that multi-line replies may not be nested.
-
- The three digits of the reply each have a special significance.
- This is intended to allow a range of very simple to very
- sophisticated responses by the user-process. The first digit
- denotes whether the response is good, bad or incomplete.
- (Referring to the state diagram), an unsophisticated user-process
- will be able to determine its next action (proceed as planned,
-
-
-Postel & Reynolds [Page 36]
-
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-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- redo, retrench, etc.) by simply examining this first digit. A
- user-process that wants to know approximately what kind of error
- occurred (e.g. file system error, command syntax error) may
- examine the second digit, reserving the third digit for the finest
- gradation of information (e.g., RNTO command without a preceding
- RNFR).
-
- There are five values for the first digit of the reply code:
-
- 1yz Positive Preliminary reply
-
- The requested action is being initiated; expect another
- reply before proceeding with a new command. (The
- user-process sending another command before the
- completion reply would be in violation of protocol; but
- server-FTP processes should queue any commands that
- arrive while a preceding command is in progress.) This
- type of reply can be used to indicate that the command
- was accepted and the user-process may now pay attention
- to the data connections, for implementations where
- simultaneous monitoring is difficult. The server-FTP
- process may send at most, one 1yz reply per command.
-
- 2yz Positive Completion reply
-
- The requested action has been successfully completed. A
- new request may be initiated.
-
- 3yz Positive Intermediate reply
-
- The command has been accepted, but the requested action
- is being held in abeyance, pending receipt of further
- information. The user should send another command
- specifying this information. This reply is used in
- command sequence groups.
-
- 4yz Transient Negative Completion reply
-
- The command was not accepted and the requested action did
- not take place, but the error condition is temporary and
- the action may be requested again. The user should
- return to the beginning of the command sequence, if any.
- It is difficult to assign a meaning to "transient",
- particularly when two distinct sites (Server- and
- User-processes) have to agree on the interpretation.
- Each reply in the 4yz category might have a slightly
- different time value, but the intent is that the
-
-
-Postel & Reynolds [Page 37]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- user-process is encouraged to try again. A rule of thumb
- in determining if a reply fits into the 4yz or the 5yz
- (Permanent Negative) category is that replies are 4yz if
- the commands can be repeated without any change in
- command form or in properties of the User or Server
- (e.g., the command is spelled the same with the same
- arguments used; the user does not change his file access
- or user name; the server does not put up a new
- implementation.)
-
- 5yz Permanent Negative Completion reply
-
- The command was not accepted and the requested action did
- not take place. The User-process is discouraged from
- repeating the exact request (in the same sequence). Even
- some "permanent" error conditions can be corrected, so
- the human user may want to direct his User-process to
- reinitiate the command sequence by direct action at some
- point in the future (e.g., after the spelling has been
- changed, or the user has altered his directory status.)
-
- The following function groupings are encoded in the second
- digit:
-
- x0z Syntax - These replies refer to syntax errors,
- syntactically correct commands that don't fit any
- functional category, unimplemented or superfluous
- commands.
-
- x1z Information - These are replies to requests for
- information, such as status or help.
-
- x2z Connections - Replies referring to the control and
- data connections.
-
- x3z Authentication and accounting - Replies for the login
- process and accounting procedures.
-
- x4z Unspecified as yet.
-
- x5z File system - These replies indicate the status of the
- Server file system vis-a-vis the requested transfer or
- other file system action.
-
- The third digit gives a finer gradation of meaning in each of
- the function categories, specified by the second digit. The
- list of replies below will illustrate this. Note that the text
-
-
-Postel & Reynolds [Page 38]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- associated with each reply is recommended, rather than
- mandatory, and may even change according to the command with
- which it is associated. The reply codes, on the other hand,
- must strictly follow the specifications in the last section;
- that is, Server implementations should not invent new codes for
- situations that are only slightly different from the ones
- described here, but rather should adapt codes already defined.
-
- A command such as TYPE or ALLO whose successful execution
- does not offer the user-process any new information will
- cause a 200 reply to be returned. If the command is not
- implemented by a particular Server-FTP process because it
- has no relevance to that computer system, for example ALLO
- at a TOPS20 site, a Positive Completion reply is still
- desired so that the simple User-process knows it can proceed
- with its course of action. A 202 reply is used in this case
- with, for example, the reply text: "No storage allocation
- necessary." If, on the other hand, the command requests a
- non-site-specific action and is unimplemented, the response
- is 502. A refinement of that is the 504 reply for a command
- that is implemented, but that requests an unimplemented
- parameter.
-
- 4.2.1 Reply Codes by Function Groups
-
- 200 Command okay.
- 500 Syntax error, command unrecognized.
- This may include errors such as command line too long.
- 501 Syntax error in parameters or arguments.
- 202 Command not implemented, superfluous at this site.
- 502 Command not implemented.
- 503 Bad sequence of commands.
- 504 Command not implemented for that parameter.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Postel & Reynolds [Page 39]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- 110 Restart marker reply.
- In this case, the text is exact and not left to the
- particular implementation; it must read:
- MARK yyyy = mmmm
- Where yyyy is User-process data stream marker, and mmmm
- server's equivalent marker (note the spaces between markers
- and "=").
- 211 System status, or system help reply.
- 212 Directory status.
- 213 File status.
- 214 Help message.
- On how to use the server or the meaning of a particular
- non-standard command. This reply is useful only to the
- human user.
- 215 NAME system type.
- Where NAME is an official system name from the list in the
- Assigned Numbers document.
-
- 120 Service ready in nnn minutes.
- 220 Service ready for new user.
- 221 Service closing control connection.
- Logged out if appropriate.
- 421 Service not available, closing control connection.
- This may be a reply to any command if the service knows it
- must shut down.
- 125 Data connection already open; transfer starting.
- 225 Data connection open; no transfer in progress.
- 425 Can't open data connection.
- 226 Closing data connection.
- Requested file action successful (for example, file
- transfer or file abort).
- 426 Connection closed; transfer aborted.
- 227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
-
- 230 User logged in, proceed.
- 530 Not logged in.
- 331 User name okay, need password.
- 332 Need account for login.
- 532 Need account for storing files.
-
-
-
-
-
-
-
-
-
-
-Postel & Reynolds [Page 40]
-
-
-
-RFC 959 October 1985
-File Transfer Protocol
-
-
- 150 File status okay; about to open data connection.
- 250 Requested file action okay, completed.
- 257 "PATHNAME" created.
- 350 Requested file action pending further information.
- 450 Requested file action not taken.
- File unavailable (e.g., file busy).
- 550 Requested action not taken.
- File unavailable (e.g., file not found, no access).
- 451 Requested action aborted. Local error in processing.
- 551 Requested action aborted. Page type unknown.
- 452 Requested action not taken.
- Insufficient storage space in system.
- 552 Requested file action aborted.
- Exceeded storage allocation (for current directory or
- dataset).
- 553 Requested action not taken.
- File name not allowed.
-
-
- 4.2.2 Numeric Order List of Reply Codes
-
- 110 Restart marker reply.
- In this case, the text is exact and not left to the
- particular implementation; it must read:
- MARK yyyy = mmmm
- Where yyyy is User-process data stream marker, and mmmm
- server's equivalent marker (note the spaces between markers
- and "=").
- 120 Service ready in nnn minutes.
- 125 Data connection already open; transfer starting.
- 150 File status okay; about to open data connection.
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
- 200 Command okay.
- 202 Command not implemented, superfluous at this site.
- 211 System status, or system help reply.
- 212 Directory status.
- 213 File status.
- 214 Help message.
- On how to use the server or the meaning of a particular
- non-standard command. This reply is useful only to the
- human user.
- 215 NAME system type.
- Where NAME is an official system name from the list in the
- Assigned Numbers document.
- 220 Service ready for new user.
- 221 Service closing control connection.
- Logged out if appropriate.
- 225 Data connection open; no transfer in progress.
- 226 Closing data connection.
- Requested file action successful (for example, file
- transfer or file abort).
- 227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
- 230 User logged in, proceed.
- 250 Requested file action okay, completed.
- 257 "PATHNAME" created.
-
- 331 User name okay, need password.
- 332 Need account for login.
- 350 Requested file action pending further information.
-
- 421 Service not available, closing control connection.
- This may be a reply to any command if the service knows it
- must shut down.
- 425 Can't open data connection.
- 426 Connection closed; transfer aborted.
- 450 Requested file action not taken.
- File unavailable (e.g., file busy).
- 451 Requested action aborted: local error in processing.
- 452 Requested action not taken.
- Insufficient storage space in system.
-
-
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-
-
- 500 Syntax error, command unrecognized.
- This may include errors such as command line too long.
- 501 Syntax error in parameters or arguments.
- 502 Command not implemented.
- 503 Bad sequence of commands.
- 504 Command not implemented for that parameter.
- 530 Not logged in.
- 532 Need account for storing files.
- 550 Requested action not taken.
- File unavailable (e.g., file not found, no access).
- 551 Requested action aborted: page type unknown.
- 552 Requested file action aborted.
- Exceeded storage allocation (for current directory or
- dataset).
- 553 Requested action not taken.
- File name not allowed.
-
-
-5. DECLARATIVE SPECIFICATIONS
-
- 5.1. MINIMUM IMPLEMENTATION
-
- In order to make FTP workable without needless error messages, the
- following minimum implementation is required for all servers:
-
- TYPE - ASCII Non-print
- MODE - Stream
- STRUCTURE - File, Record
- COMMANDS - USER, QUIT, PORT,
- TYPE, MODE, STRU,
- for the default values
- RETR, STOR,
- NOOP.
-
- The default values for transfer parameters are:
-
- TYPE - ASCII Non-print
- MODE - Stream
- STRU - File
-
- All hosts must accept the above as the standard defaults.
-
-
-
-
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-
-
- 5.2. CONNECTIONS
-
- The server protocol interpreter shall "listen" on Port L. The
- user or user protocol interpreter shall initiate the full-duplex
- control connection. Server- and user- processes should follow the
- conventions of the Telnet protocol as specified in the
- ARPA-Internet Protocol Handbook [1]. Servers are under no
- obligation to provide for editing of command lines and may require
- that it be done in the user host. The control connection shall be
- closed by the server at the user's request after all transfers and
- replies are completed.
-
- The user-DTP must "listen" on the specified data port; this may be
- the default user port (U) or a port specified in the PORT command.
- The server shall initiate the data connection from his own default
- data port (L-1) using the specified user data port. The direction
- of the transfer and the port used will be determined by the FTP
- service command.
-
- Note that all FTP implementation must support data transfer using
- the default port, and that only the USER-PI may initiate the use
- of non-default ports.
-
- When data is to be transferred between two servers, A and B (refer
- to Figure 2), the user-PI, C, sets up control connections with
- both server-PI's. One of the servers, say A, is then sent a PASV
- command telling him to "listen" on his data port rather than
- initiate a connection when he receives a transfer service command.
- When the user-PI receives an acknowledgment to the PASV command,
- which includes the identity of the host and port being listened
- on, the user-PI then sends A's port, a, to B in a PORT command; a
- reply is returned. The user-PI may then send the corresponding
- service commands to A and B. Server B initiates the connection
- and the transfer proceeds. The command-reply sequence is listed
- below where the messages are vertically synchronous but
- horizontally asynchronous:
-
-
-
-
-
-
-
-
-
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-
-
- User-PI - Server A User-PI - Server B
- ------------------ ------------------
-
- C->A : Connect C->B : Connect
- C->A : PASV
- A->C : 227 Entering Passive Mode. A1,A2,A3,A4,a1,a2
- C->B : PORT A1,A2,A3,A4,a1,a2
- B->C : 200 Okay
- C->A : STOR C->B : RETR
- B->A : Connect to HOST-A, PORT-a
-
- Figure 3
-
- The data connection shall be closed by the server under the
- conditions described in the Section on Establishing Data
- Connections. If the data connection is to be closed following a
- data transfer where closing the connection is not required to
- indicate the end-of-file, the server must do so immediately.
- Waiting until after a new transfer command is not permitted
- because the user-process will have already tested the data
- connection to see if it needs to do a "listen"; (remember that the
- user must "listen" on a closed data port BEFORE sending the
- transfer request). To prevent a race condition here, the server
- sends a reply (226) after closing the data connection (or if the
- connection is left open, a "file transfer completed" reply (250)
- and the user-PI should wait for one of these replies before
- issuing a new transfer command).
-
- Any time either the user or server see that the connection is
- being closed by the other side, it should promptly read any
- remaining data queued on the connection and issue the close on its
- own side.
-
- 5.3. COMMANDS
-
- The commands are Telnet character strings transmitted over the
- control connections as described in the Section on FTP Commands.
- The command functions and semantics are described in the Section
- on Access Control Commands, Transfer Parameter Commands, FTP
- Service Commands, and Miscellaneous Commands. The command syntax
- is specified here.
-
- The commands begin with a command code followed by an argument
- field. The command codes are four or fewer alphabetic characters.
- Upper and lower case alphabetic characters are to be treated
- identically. Thus, any of the following may represent the
- retrieve command:
-
-
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-
-
- RETR Retr retr ReTr rETr
-
- This also applies to any symbols representing parameter values,
- such as A or a for ASCII TYPE. The command codes and the argument
- fields are separated by one or more spaces.
-
- The argument field consists of a variable length character string
- ending with the character sequence <CRLF> (Carriage Return, Line
- Feed) for NVT-ASCII representation; for other negotiated languages
- a different end of line character might be used. It should be
- noted that the server is to take no action until the end of line
- code is received.
-
- The syntax is specified below in NVT-ASCII. All characters in the
- argument field are ASCII characters including any ASCII
- represented decimal integers. Square brackets denote an optional
- argument field. If the option is not taken, the appropriate
- default is implied.
-
-
-
-
-
-
-
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-
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-
-
- 5.3.1. FTP COMMANDS
-
- The following are the FTP commands:
-
- USER <SP> <username> <CRLF>
- PASS <SP> <password> <CRLF>
- ACCT <SP> <account-information> <CRLF>
- CWD <SP> <pathname> <CRLF>
- CDUP <CRLF>
- SMNT <SP> <pathname> <CRLF>
- QUIT <CRLF>
- REIN <CRLF>
- PORT <SP> <host-port> <CRLF>
- PASV <CRLF>
- TYPE <SP> <type-code> <CRLF>
- STRU <SP> <structure-code> <CRLF>
- MODE <SP> <mode-code> <CRLF>
- RETR <SP> <pathname> <CRLF>
- STOR <SP> <pathname> <CRLF>
- STOU <CRLF>
- APPE <SP> <pathname> <CRLF>
- ALLO <SP> <decimal-integer>
- [<SP> R <SP> <decimal-integer>] <CRLF>
- REST <SP> <marker> <CRLF>
- RNFR <SP> <pathname> <CRLF>
- RNTO <SP> <pathname> <CRLF>
- ABOR <CRLF>
- DELE <SP> <pathname> <CRLF>
- RMD <SP> <pathname> <CRLF>
- MKD <SP> <pathname> <CRLF>
- PWD <CRLF>
- LIST [<SP> <pathname>] <CRLF>
- NLST [<SP> <pathname>] <CRLF>
- SITE <SP> <string> <CRLF>
- SYST <CRLF>
- STAT [<SP> <pathname>] <CRLF>
- HELP [<SP> <string>] <CRLF>
- NOOP <CRLF>
-
-
-
-
-
-
-
-
-
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-
-
- 5.3.2. FTP COMMAND ARGUMENTS
-
- The syntax of the above argument fields (using BNF notation
- where applicable) is:
-
- <username> ::= <string>
- <password> ::= <string>
- <account-information> ::= <string>
- <string> ::= <char> | <char><string>
- <char> ::= any of the 128 ASCII characters except <CR> and
- <LF>
- <marker> ::= <pr-string>
- <pr-string> ::= <pr-char> | <pr-char><pr-string>
- <pr-char> ::= printable characters, any
- ASCII code 33 through 126
- <byte-size> ::= <number>
- <host-port> ::= <host-number>,<port-number>
- <host-number> ::= <number>,<number>,<number>,<number>
- <port-number> ::= <number>,<number>
- <number> ::= any decimal integer 1 through 255
- <form-code> ::= N | T | C
- <type-code> ::= A [<sp> <form-code>]
- | E [<sp> <form-code>]
- | I
- | L <sp> <byte-size>
- <structure-code> ::= F | R | P
- <mode-code> ::= S | B | C
- <pathname> ::= <string>
- <decimal-integer> ::= any decimal integer
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
- 5.4. SEQUENCING OF COMMANDS AND REPLIES
-
- The communication between the user and server is intended to be an
- alternating dialogue. As such, the user issues an FTP command and
- the server responds with a prompt primary reply. The user should
- wait for this initial primary success or failure response before
- sending further commands.
-
- Certain commands require a second reply for which the user should
- also wait. These replies may, for example, report on the progress
- or completion of file transfer or the closing of the data
- connection. They are secondary replies to file transfer commands.
-
- One important group of informational replies is the connection
- greetings. Under normal circumstances, a server will send a 220
- reply, "awaiting input", when the connection is completed. The
- user should wait for this greeting message before sending any
- commands. If the server is unable to accept input right away, a
- 120 "expected delay" reply should be sent immediately and a 220
- reply when ready. The user will then know not to hang up if there
- is a delay.
-
- Spontaneous Replies
-
- Sometimes "the system" spontaneously has a message to be sent
- to a user (usually all users). For example, "System going down
- in 15 minutes". There is no provision in FTP for such
- spontaneous information to be sent from the server to the user.
- It is recommended that such information be queued in the
- server-PI and delivered to the user-PI in the next reply
- (possibly making it a multi-line reply).
-
- The table below lists alternative success and failure replies for
- each command. These must be strictly adhered to; a server may
- substitute text in the replies, but the meaning and action implied
- by the code numbers and by the specific command reply sequence
- cannot be altered.
-
- Command-Reply Sequences
-
- In this section, the command-reply sequence is presented. Each
- command is listed with its possible replies; command groups are
- listed together. Preliminary replies are listed first (with
- their succeeding replies indented and under them), then
- positive and negative completion, and finally intermediary
-
-
-
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-File Transfer Protocol
-
-
- replies with the remaining commands from the sequence
- following. This listing forms the basis for the state
- diagrams, which will be presented separately.
-
- Connection Establishment
- 120
- 220
- 220
- 421
- Login
- USER
- 230
- 530
- 500, 501, 421
- 331, 332
- PASS
- 230
- 202
- 530
- 500, 501, 503, 421
- 332
- ACCT
- 230
- 202
- 530
- 500, 501, 503, 421
- CWD
- 250
- 500, 501, 502, 421, 530, 550
- CDUP
- 200
- 500, 501, 502, 421, 530, 550
- SMNT
- 202, 250
- 500, 501, 502, 421, 530, 550
- Logout
- REIN
- 120
- 220
- 220
- 421
- 500, 502
- QUIT
- 221
- 500
-
-
-
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-
-
- Transfer parameters
- PORT
- 200
- 500, 501, 421, 530
- PASV
- 227
- 500, 501, 502, 421, 530
- MODE
- 200
- 500, 501, 504, 421, 530
- TYPE
- 200
- 500, 501, 504, 421, 530
- STRU
- 200
- 500, 501, 504, 421, 530
- File action commands
- ALLO
- 200
- 202
- 500, 501, 504, 421, 530
- REST
- 500, 501, 502, 421, 530
- 350
- STOR
- 125, 150
- (110)
- 226, 250
- 425, 426, 451, 551, 552
- 532, 450, 452, 553
- 500, 501, 421, 530
- STOU
- 125, 150
- (110)
- 226, 250
- 425, 426, 451, 551, 552
- 532, 450, 452, 553
- 500, 501, 421, 530
- RETR
- 125, 150
- (110)
- 226, 250
- 425, 426, 451
- 450, 550
- 500, 501, 421, 530
-
-
-
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-
-
- LIST
- 125, 150
- 226, 250
- 425, 426, 451
- 450
- 500, 501, 502, 421, 530
- NLST
- 125, 150
- 226, 250
- 425, 426, 451
- 450
- 500, 501, 502, 421, 530
- APPE
- 125, 150
- (110)
- 226, 250
- 425, 426, 451, 551, 552
- 532, 450, 550, 452, 553
- 500, 501, 502, 421, 530
- RNFR
- 450, 550
- 500, 501, 502, 421, 530
- 350
- RNTO
- 250
- 532, 553
- 500, 501, 502, 503, 421, 530
- DELE
- 250
- 450, 550
- 500, 501, 502, 421, 530
- RMD
- 250
- 500, 501, 502, 421, 530, 550
- MKD
- 257
- 500, 501, 502, 421, 530, 550
- PWD
- 257
- 500, 501, 502, 421, 550
- ABOR
- 225, 226
- 500, 501, 502, 421
-
-
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-
-
- Informational commands
- SYST
- 215
- 500, 501, 502, 421
- STAT
- 211, 212, 213
- 450
- 500, 501, 502, 421, 530
- HELP
- 211, 214
- 500, 501, 502, 421
- Miscellaneous commands
- SITE
- 200
- 202
- 500, 501, 530
- NOOP
- 200
- 500 421
-
-
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-File Transfer Protocol
-
-
-6. STATE DIAGRAMS
-
- Here we present state diagrams for a very simple minded FTP
- implementation. Only the first digit of the reply codes is used.
- There is one state diagram for each group of FTP commands or command
- sequences.
-
- The command groupings were determined by constructing a model for
- each command then collecting together the commands with structurally
- identical models.
-
- For each command or command sequence there are three possible
- outcomes: success (S), failure (F), and error (E). In the state
- diagrams below we use the symbol B for "begin", and the symbol W for
- "wait for reply".
-
- We first present the diagram that represents the largest group of FTP
- commands:
-
-
- 1,3 +---+
- ----------->| E |
- | +---+
- |
- +---+ cmd +---+ 2 +---+
- | B |---------->| W |---------->| S |
- +---+ +---+ +---+
- |
- | 4,5 +---+
- ----------->| F |
- +---+
-
-
- This diagram models the commands:
-
- ABOR, ALLO, DELE, CWD, CDUP, SMNT, HELP, MODE, NOOP, PASV,
- QUIT, SITE, PORT, SYST, STAT, RMD, MKD, PWD, STRU, and TYPE.
-
-
-
-
-
-
-
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-
-
- The other large group of commands is represented by a very similar
- diagram:
-
-
- 3 +---+
- ----------->| E |
- | +---+
- |
- +---+ cmd +---+ 2 +---+
- | B |---------->| W |---------->| S |
- +---+ --->+---+ +---+
- | | |
- | | | 4,5 +---+
- | 1 | ----------->| F |
- ----- +---+
-
-
- This diagram models the commands:
-
- APPE, LIST, NLST, REIN, RETR, STOR, and STOU.
-
- Note that this second model could also be used to represent the first
- group of commands, the only difference being that in the first group
- the 100 series replies are unexpected and therefore treated as error,
- while the second group expects (some may require) 100 series replies.
- Remember that at most, one 100 series reply is allowed per command.
-
- The remaining diagrams model command sequences, perhaps the simplest
- of these is the rename sequence:
-
-
- +---+ RNFR +---+ 1,2 +---+
- | B |---------->| W |---------->| E |
- +---+ +---+ -->+---+
- | | |
- 3 | | 4,5 |
- -------------- ------ |
- | | | +---+
- | ------------->| S |
- | | 1,3 | | +---+
- | 2| --------
- | | | |
- V | | |
- +---+ RNTO +---+ 4,5 ----->+---+
- | |---------->| W |---------->| F |
- +---+ +---+ +---+
-
-
-
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-File Transfer Protocol
-
-
- The next diagram is a simple model of the Restart command:
-
-
- +---+ REST +---+ 1,2 +---+
- | B |---------->| W |---------->| E |
- +---+ +---+ -->+---+
- | | |
- 3 | | 4,5 |
- -------------- ------ |
- | | | +---+
- | ------------->| S |
- | | 3 | | +---+
- | 2| --------
- | | | |
- V | | |
- +---+ cmd +---+ 4,5 ----->+---+
- | |---------->| W |---------->| F |
- +---+ -->+---+ +---+
- | |
- | 1 |
- ------
-
-
- Where "cmd" is APPE, STOR, or RETR.
-
- We note that the above three models are similar. The Restart differs
- from the Rename two only in the treatment of 100 series replies at
- the second stage, while the second group expects (some may require)
- 100 series replies. Remember that at most, one 100 series reply is
- allowed per command.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Postel & Reynolds [Page 56]
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-
-
- The most complicated diagram is for the Login sequence:
-
-
- 1
- +---+ USER +---+------------->+---+
- | B |---------->| W | 2 ---->| E |
- +---+ +---+------ | -->+---+
- | | | | |
- 3 | | 4,5 | | |
- -------------- ----- | | |
- | | | | |
- | | | | |
- | --------- |
- | 1| | | |
- V | | | |
- +---+ PASS +---+ 2 | ------>+---+
- | |---------->| W |------------->| S |
- +---+ +---+ ---------->+---+
- | | | | |
- 3 | |4,5| | |
- -------------- -------- |
- | | | | |
- | | | | |
- | -----------
- | 1,3| | | |
- V | 2| | |
- +---+ ACCT +---+-- | ----->+---+
- | |---------->| W | 4,5 -------->| F |
- +---+ +---+------------->+---+
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
- Finally, we present a generalized diagram that could be used to model
- the command and reply interchange:
-
-
- ------------------------------------
- | |
- Begin | |
- | V |
- | +---+ cmd +---+ 2 +---+ |
- -->| |------->| |---------->| | |
- | | | W | | S |-----|
- -->| | -->| |----- | | |
- | +---+ | +---+ 4,5 | +---+ |
- | | | | | | |
- | | | 1| |3 | +---+ |
- | | | | | | | | |
- | | ---- | ---->| F |-----
- | | | | |
- | | | +---+
- -------------------
- |
- |
- V
- End
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
-7. TYPICAL FTP SCENARIO
-
- User at host U wanting to transfer files to/from host S:
-
- In general, the user will communicate to the server via a mediating
- user-FTP process. The following may be a typical scenario. The
- user-FTP prompts are shown in parentheses, '---->' represents
- commands from host U to host S, and '<----' represents replies from
- host S to host U.
-
- LOCAL COMMANDS BY USER ACTION INVOLVED
-
- ftp (host) multics<CR> Connect to host S, port L,
- establishing control connections.
- <---- 220 Service ready <CRLF>.
- username Doe <CR> USER Doe<CRLF>---->
- <---- 331 User name ok,
- need password<CRLF>.
- password mumble <CR> PASS mumble<CRLF>---->
- <---- 230 User logged in<CRLF>.
- retrieve (local type) ASCII<CR>
- (local pathname) test 1 <CR> User-FTP opens local file in ASCII.
- (for. pathname) test.pl1<CR> RETR test.pl1<CRLF> ---->
- <---- 150 File status okay;
- about to open data
- connection<CRLF>.
- Server makes data connection
- to port U.
-
- <---- 226 Closing data connection,
- file transfer successful<CRLF>.
- type Image<CR> TYPE I<CRLF> ---->
- <---- 200 Command OK<CRLF>
- store (local type) image<CR>
- (local pathname) file dump<CR> User-FTP opens local file in Image.
- (for.pathname) >udd>cn>fd<CR> STOR >udd>cn>fd<CRLF> ---->
- <---- 550 Access denied<CRLF>
- terminate QUIT <CRLF> ---->
- Server closes all
- connections.
-
-8. CONNECTION ESTABLISHMENT
-
- The FTP control connection is established via TCP between the user
- process port U and the server process port L. This protocol is
- assigned the service port 21 (25 octal), that is L=21.
-
-
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-APPENDIX I - PAGE STRUCTURE
-
- The need for FTP to support page structure derives principally from
- the need to support efficient transmission of files between TOPS-20
- systems, particularly the files used by NLS.
-
- The file system of TOPS-20 is based on the concept of pages. The
- operating system is most efficient at manipulating files as pages.
- The operating system provides an interface to the file system so that
- many applications view files as sequential streams of characters.
- However, a few applications use the underlying page structures
- directly, and some of these create holey files.
-
- A TOPS-20 disk file consists of four things: a pathname, a page
- table, a (possibly empty) set of pages, and a set of attributes.
-
- The pathname is specified in the RETR or STOR command. It includes
- the directory name, file name, file name extension, and generation
- number.
-
- The page table contains up to 2**18 entries. Each entry may be
- EMPTY, or may point to a page. If it is not empty, there are also
- some page-specific access bits; not all pages of a file need have the
- same access protection.
-
- A page is a contiguous set of 512 words of 36 bits each.
-
- The attributes of the file, in the File Descriptor Block (FDB),
- contain such things as creation time, write time, read time, writer's
- byte-size, end-of-file pointer, count of reads and writes, backup
- system tape numbers, etc.
-
- Note that there is NO requirement that entries in the page table be
- contiguous. There may be empty page table slots between occupied
- ones. Also, the end of file pointer is simply a number. There is no
- requirement that it in fact point at the "last" datum in the file.
- Ordinary sequential I/O calls in TOPS-20 will cause the end of file
- pointer to be left after the last datum written, but other operations
- may cause it not to be so, if a particular programming system so
- requires.
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- In fact, in both of these special cases, "holey" files and
- end-of-file pointers NOT at the end of the file, occur with NLS data
- files.
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- The TOPS-20 paged files can be sent with the FTP transfer parameters:
- TYPE L 36, STRU P, and MODE S (in fact, any mode could be used).
-
- Each page of information has a header. Each header field, which is a
- logical byte, is a TOPS-20 word, since the TYPE is L 36.
-
- The header fields are:
-
- Word 0: Header Length.
-
- The header length is 5.
-
- Word 1: Page Index.
-
- If the data is a disk file page, this is the number of that
- page in the file's page map. Empty pages (holes) in the file
- are simply not sent. Note that a hole is NOT the same as a
- page of zeros.
-
- Word 2: Data Length.
-
- The number of data words in this page, following the header.
- Thus, the total length of the transmission unit is the Header
- Length plus the Data Length.
-
- Word 3: Page Type.
-
- A code for what type of chunk this is. A data page is type 3,
- the FDB page is type 2.
-
- Word 4: Page Access Control.
-
- The access bits associated with the page in the file's page
- map. (This full word quantity is put into AC2 of an SPACS by
- the program reading from net to disk.)
-
- After the header are Data Length data words. Data Length is
- currently either 512 for a data page or 31 for an FDB. Trailing
- zeros in a disk file page may be discarded, making Data Length less
- than 512 in that case.
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-APPENDIX II - DIRECTORY COMMANDS
-
- Since UNIX has a tree-like directory structure in which directories
- are as easy to manipulate as ordinary files, it is useful to expand
- the FTP servers on these machines to include commands which deal with
- the creation of directories. Since there are other hosts on the
- ARPA-Internet which have tree-like directories (including TOPS-20 and
- Multics), these commands are as general as possible.
-
- Four directory commands have been added to FTP:
-
- MKD pathname
-
- Make a directory with the name "pathname".
-
- RMD pathname
-
- Remove the directory with the name "pathname".
-
- PWD
-
- Print the current working directory name.
-
- CDUP
-
- Change to the parent of the current working directory.
-
- The "pathname" argument should be created (removed) as a
- subdirectory of the current working directory, unless the "pathname"
- string contains sufficient information to specify otherwise to the
- server, e.g., "pathname" is an absolute pathname (in UNIX and
- Multics), or pathname is something like "<abso.lute.path>" to
- TOPS-20.
-
- REPLY CODES
-
- The CDUP command is a special case of CWD, and is included to
- simplify the implementation of programs for transferring directory
- trees between operating systems having different syntaxes for
- naming the parent directory. The reply codes for CDUP be
- identical to the reply codes of CWD.
-
- The reply codes for RMD be identical to the reply codes for its
- file analogue, DELE.
-
- The reply codes for MKD, however, are a bit more complicated. A
- freshly created directory will probably be the object of a future
-
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- CWD command. Unfortunately, the argument to MKD may not always be
- a suitable argument for CWD. This is the case, for example, when
- a TOPS-20 subdirectory is created by giving just the subdirectory
- name. That is, with a TOPS-20 server FTP, the command sequence
-
- MKD MYDIR
- CWD MYDIR
-
- will fail. The new directory may only be referred to by its
- "absolute" name; e.g., if the MKD command above were issued while
- connected to the directory <DFRANKLIN>, the new subdirectory
- could only be referred to by the name <DFRANKLIN.MYDIR>.
-
- Even on UNIX and Multics, however, the argument given to MKD may
- not be suitable. If it is a "relative" pathname (i.e., a pathname
- which is interpreted relative to the current directory), the user
- would need to be in the same current directory in order to reach
- the subdirectory. Depending on the application, this may be
- inconvenient. It is not very robust in any case.
-
- To solve these problems, upon successful completion of an MKD
- command, the server should return a line of the form:
-
- 257<space>"<directory-name>"<space><commentary>
-
- That is, the server will tell the user what string to use when
- referring to the created directory. The directory name can
- contain any character; embedded double-quotes should be escaped by
- double-quotes (the "quote-doubling" convention).
-
- For example, a user connects to the directory /usr/dm, and creates
- a subdirectory, named pathname:
-
- CWD /usr/dm
- 200 directory changed to /usr/dm
- MKD pathname
- 257 "/usr/dm/pathname" directory created
-
- An example with an embedded double quote:
-
- MKD foo"bar
- 257 "/usr/dm/foo""bar" directory created
- CWD /usr/dm/foo"bar
- 200 directory changed to /usr/dm/foo"bar
-
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- The prior existence of a subdirectory with the same name is an
- error, and the server must return an "access denied" error reply
- in that case.
-
- CWD /usr/dm
- 200 directory changed to /usr/dm
- MKD pathname
- 521-"/usr/dm/pathname" directory already exists;
- 521 taking no action.
-
- The failure replies for MKD are analogous to its file creating
- cousin, STOR. Also, an "access denied" return is given if a file
- name with the same name as the subdirectory will conflict with the
- creation of the subdirectory (this is a problem on UNIX, but
- shouldn't be one on TOPS-20).
-
- Essentially because the PWD command returns the same type of
- information as the successful MKD command, the successful PWD
- command uses the 257 reply code as well.
-
- SUBTLETIES
-
- Because these commands will be most useful in transferring
- subtrees from one machine to another, carefully observe that the
- argument to MKD is to be interpreted as a sub-directory of the
- current working directory, unless it contains enough information
- for the destination host to tell otherwise. A hypothetical
- example of its use in the TOPS-20 world:
-
- CWD <some.where>
- 200 Working directory changed
- MKD overrainbow
- 257 "<some.where.overrainbow>" directory created
- CWD overrainbow
- 431 No such directory
- CWD <some.where.overrainbow>
- 200 Working directory changed
-
- CWD <some.where>
- 200 Working directory changed to <some.where>
- MKD <unambiguous>
- 257 "<unambiguous>" directory created
- CWD <unambiguous>
-
- Note that the first example results in a subdirectory of the
- connected directory. In contrast, the argument in the second
- example contains enough information for TOPS-20 to tell that the
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- <unambiguous> directory is a top-level directory. Note also that
- in the first example the user "violated" the protocol by
- attempting to access the freshly created directory with a name
- other than the one returned by TOPS-20. Problems could have
- resulted in this case had there been an <overrainbow> directory;
- this is an ambiguity inherent in some TOPS-20 implementations.
- Similar considerations apply to the RMD command. The point is
- this: except where to do so would violate a host's conventions for
- denoting relative versus absolute pathnames, the host should treat
- the operands of the MKD and RMD commands as subdirectories. The
- 257 reply to the MKD command must always contain the absolute
- pathname of the created directory.
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-APPENDIX III - RFCs on FTP
-
- Bhushan, Abhay, "A File Transfer Protocol", RFC 114 (NIC 5823),
- MIT-Project MAC, 16 April 1971.
-
- Harslem, Eric, and John Heafner, "Comments on RFC 114 (A File
- Transfer Protocol)", RFC 141 (NIC 6726), RAND, 29 April 1971.
-
- Bhushan, Abhay, et al, "The File Transfer Protocol", RFC 172
- (NIC 6794), MIT-Project MAC, 23 June 1971.
-
- Braden, Bob, "Comments on DTP and FTP Proposals", RFC 238 (NIC 7663),
- UCLA/CCN, 29 September 1971.
-
- Bhushan, Abhay, et al, "The File Transfer Protocol", RFC 265
- (NIC 7813), MIT-Project MAC, 17 November 1971.
-
- McKenzie, Alex, "A Suggested Addition to File Transfer Protocol",
- RFC 281 (NIC 8163), BBN, 8 December 1971.
-
- Bhushan, Abhay, "The Use of "Set Data Type" Transaction in File
- Transfer Protocol", RFC 294 (NIC 8304), MIT-Project MAC,
- 25 January 1972.
-
- Bhushan, Abhay, "The File Transfer Protocol", RFC 354 (NIC 10596),
- MIT-Project MAC, 8 July 1972.
-
- Bhushan, Abhay, "Comments on the File Transfer Protocol (RFC 354)",
- RFC 385 (NIC 11357), MIT-Project MAC, 18 August 1972.
-
- Hicks, Greg, "User FTP Documentation", RFC 412 (NIC 12404), Utah,
- 27 November 1972.
-
- Bhushan, Abhay, "File Transfer Protocol (FTP) Status and Further
- Comments", RFC 414 (NIC 12406), MIT-Project MAC, 20 November 1972.
-
- Braden, Bob, "Comments on File Transfer Protocol", RFC 430
- (NIC 13299), UCLA/CCN, 7 February 1973.
-
- Thomas, Bob, and Bob Clements, "FTP Server-Server Interaction",
- RFC 438 (NIC 13770), BBN, 15 January 1973.
-
- Braden, Bob, "Print Files in FTP", RFC 448 (NIC 13299), UCLA/CCN,
- 27 February 1973.
-
- McKenzie, Alex, "File Transfer Protocol", RFC 454 (NIC 14333), BBN,
- 16 February 1973.
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- Bressler, Bob, and Bob Thomas, "Mail Retrieval via FTP", RFC 458
- (NIC 14378), BBN-NET and BBN-TENEX, 20 February 1973.
-
- Neigus, Nancy, "File Transfer Protocol", RFC 542 (NIC 17759), BBN,
- 12 July 1973.
-
- Krilanovich, Mark, and George Gregg, "Comments on the File Transfer
- Protocol", RFC 607 (NIC 21255), UCSB, 7 January 1974.
-
- Pogran, Ken, and Nancy Neigus, "Response to RFC 607 - Comments on the
- File Transfer Protocol", RFC 614 (NIC 21530), BBN, 28 January 1974.
-
- Krilanovich, Mark, George Gregg, Wayne Hathaway, and Jim White,
- "Comments on the File Transfer Protocol", RFC 624 (NIC 22054), UCSB,
- Ames Research Center, SRI-ARC, 28 February 1974.
-
- Bhushan, Abhay, "FTP Comments and Response to RFC 430", RFC 463
- (NIC 14573), MIT-DMCG, 21 February 1973.
-
- Braden, Bob, "FTP Data Compression", RFC 468 (NIC 14742), UCLA/CCN,
- 8 March 1973.
-
- Bhushan, Abhay, "FTP and Network Mail System", RFC 475 (NIC 14919),
- MIT-DMCG, 6 March 1973.
-
- Bressler, Bob, and Bob Thomas "FTP Server-Server Interaction - II",
- RFC 478 (NIC 14947), BBN-NET and BBN-TENEX, 26 March 1973.
-
- White, Jim, "Use of FTP by the NIC Journal", RFC 479 (NIC 14948),
- SRI-ARC, 8 March 1973.
-
- White, Jim, "Host-Dependent FTP Parameters", RFC 480 (NIC 14949),
- SRI-ARC, 8 March 1973.
-
- Padlipsky, Mike, "An FTP Command-Naming Problem", RFC 506
- (NIC 16157), MIT-Multics, 26 June 1973.
-
- Day, John, "Memo to FTP Group (Proposal for File Access Protocol)",
- RFC 520 (NIC 16819), Illinois, 25 June 1973.
-
- Merryman, Robert, "The UCSD-CC Server-FTP Facility", RFC 532
- (NIC 17451), UCSD-CC, 22 June 1973.
-
- Braden, Bob, "TENEX FTP Problem", RFC 571 (NIC 18974), UCLA/CCN,
- 15 November 1973.
-
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- McKenzie, Alex, and Jon Postel, "Telnet and FTP Implementation -
- Schedule Change", RFC 593 (NIC 20615), BBN and MITRE,
- 29 November 1973.
-
- Sussman, Julie, "FTP Error Code Usage for More Reliable Mail
- Service", RFC 630 (NIC 30237), BBN, 10 April 1974.
-
- Postel, Jon, "Revised FTP Reply Codes", RFC 640 (NIC 30843),
- UCLA/NMC, 5 June 1974.
-
- Harvey, Brian, "Leaving Well Enough Alone", RFC 686 (NIC 32481),
- SU-AI, 10 May 1975.
-
- Harvey, Brian, "One More Try on the FTP", RFC 691 (NIC 32700), SU-AI,
- 28 May 1975.
-
- Lieb, J., "CWD Command of FTP", RFC 697 (NIC 32963), 14 July 1975.
-
- Harrenstien, Ken, "FTP Extension: XSEN", RFC 737 (NIC 42217), SRI-KL,
- 31 October 1977.
-
- Harrenstien, Ken, "FTP Extension: XRSQ/XRCP", RFC 743 (NIC 42758),
- SRI-KL, 30 December 1977.
-
- Lebling, P. David, "Survey of FTP Mail and MLFL", RFC 751, MIT,
- 10 December 1978.
-
- Postel, Jon, "File Transfer Protocol Specification", RFC 765, ISI,
- June 1980.
-
- Mankins, David, Dan Franklin, and Buzz Owen, "Directory Oriented FTP
- Commands", RFC 776, BBN, December 1980.
-
- Padlipsky, Michael, "FTP Unique-Named Store Command", RFC 949, MITRE,
- July 1985.
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-REFERENCES
-
- [1] Feinler, Elizabeth, "Internet Protocol Transition Workbook",
- Network Information Center, SRI International, March 1982.
-
- [2] Postel, Jon, "Transmission Control Protocol - DARPA Internet
- Program Protocol Specification", RFC 793, DARPA, September 1981.
-
- [3] Postel, Jon, and Joyce Reynolds, "Telnet Protocol
- Specification", RFC 854, ISI, May 1983.
-
- [4] Reynolds, Joyce, and Jon Postel, "Assigned Numbers", RFC 943,
- ISI, April 1985.
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