<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> <year>2004</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/. Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License. </legalnotice> <title>Definition of Manager Net if</title> <prepared></prepared> <responsible></responsible> <docno></docno> <approved></approved> <checked></checked> <date></date> <rev></rev> <file>snmp_manager_netif.xml</file> </header> <p></p> <image file="snmp_manager_netif_1.gif"> <icaption>The Purpose of Manager Net if</icaption> </image> <p>The Network Interface (Net if) process delivers SNMP PDUs to the manager server, and receives SNMP PDUs from the manager server. The most common behaviour of a Net if process is that is receives request PDU from the manager server, encodes the PDU into bytes and transmits the bytes onto the network to an agent. When the reply from the agent is received by the Net if process, which it decodes into an SNMP PDU, which it sends to the manager server. </p> <p>However, that simple behaviour can be modified in numerous ways. For example, the Net if process can apply some kind of encrypting/decrypting scheme on the bytes. </p> <p>The snmp application provides two different modules, <c>snmpm_net_if</c> (the default) and <c>snmpm_net_if_mt</c>, both uses the UDP as the transport protocol. The difference between the two modules is that the latter is "multi-threaded", i.e. for each message/request a new process is created that process the message/request and then exits. </p> <p>It is also possible to write your own Net if process, this section describes how to write a Net if processdo that.</p> <section> <marker id="mandatory_functions"></marker> <title>Mandatory Functions</title> <p>A Net if process must implement the SNMP manager <seealso marker="snmpm_network_interface">network interface behaviour</seealso>. </p> </section> <section> <title>Messages</title> <p>The section <em>Messages</em> describes mandatory messages, which Net if must send to the manager server process. </p> <p>Net if must send the following message when it receives an SNMP PDU from the network that is aimed for the MasterAgent: </p> <pre> Server ! {snmp_pdu, Pdu, Addr, Port} </pre> <list type="bulleted"> <item> <p><c>Pdu</c> is an SNMP PDU record, as defined in <c>snmp_types.hrl</c>, with the SNMP request.</p> </item> <item> <p><c>Addr</c> is the source address. </p> </item> <item> <p><c>Port</c> is port number of the sender.</p> </item> </list> <pre> Server ! {snmp_trap, Trap, Addr, Port} </pre> <list type="bulleted"> <item> <p><c>Trap</c> is either an SNMP pdu record or an trappdu record, as defined in <c>snmp_types.hrl</c>, with the SNMP request.</p> </item> <item> <p><c>Addr</c> is the source address. </p> </item> <item> <p><c>Port</c> is port number of the sender.</p> </item> </list> <pre> Server ! {snmp_inform, Ref, Pdu, PduMS, Addr, Port} </pre> <list type="bulleted"> <item> <p><c>Ref</c> is either the atom <c>ignore</c> or something that can be used to identify the inform-request (e.g. request-id). <c>ignore</c> is used if the response (acknowledgment) to the inform-request has already been sent (this means that the server will not make the call to the <seealso marker="snmpm_network_interface#inform_response">inform_response</seealso> function). See the <seealso marker="snmp_app">inform request behaviour</seealso> configuration option for more info.</p> </item> <item> <p><c>Pdu</c> is an SNMP PDU record, as defined in <c>snmp_types.hrl</c>, with the SNMP request.</p> </item> <item> <p><c>Addr</c> is the source address. </p> </item> <item> <p><c>Port</c> is port number of the sender.</p> </item> </list> <pre> Server ! {snmp_report, Data, Addr, Port} </pre> <list type="bulleted"> <item> <p><c>Data</c> is either <c>{ok, Pdu}</c> or <c>{error, ReqId, ReasonInfo, Pdu}</c>. Which one is used depends on the return value from the MPD <seealso marker="snmpm_mpd#process_msg">process_msg</seealso> function. If the MsgData is <c>ok</c>, the first is used, and if it is <c>{error, ReqId, Reason}</c> the latter is used.</p> </item> <item> <p><c>Pdu</c> is an SNMP PDU record, as defined in <c>snmp_types.hrl</c>, with the SNMP request.</p> </item> <item> <p><c>ReqId</c> is an integer.</p> </item> <item> <p><c>ReasonInfo</c> is a term().</p> </item> <item> <p><c>Addr</c> is the source address. </p> </item> <item> <p><c>Port</c> is port number of the sender.</p> </item> </list> <section> <title>Notes</title> <p>Since the Net if process is responsible for encoding and decoding of SNMP messages, it must also update the relevant counters in the SNMP group in MIB-II. It can use the functions in the module <c>snmpm_mpd</c> for this purpose (refer to the Reference Manual, section <c>snmp</c>, module <c>snmpm_mpd</c> for more details). </p> <p>There are also some useful functions for encoding and decoding of SNMP messages in the module <c>snmp_pdus</c>. </p> </section> </section> </chapter>