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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2004</year><year>2014</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions 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 UDP as the transport protocol i.e the transport domains
<c>transportDomainUdpIpv4</c> and/or <c>transportDomainUdpIpv6</c>.
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 processes the message/request and then exits. </p>
<p>It is also possible to write your own Net if process and
this section describes how to do 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>In this section a <c>Domain</c> field is the transport domain i.e
one of <c>transportDomainUdpIpv4</c> or <c>transportDomainUdpIpv6</c>,
and an <c>Addr</c> field is an
<c>{<seealso marker="kernel:inet#type-ip_address">IpAddr</seealso>,
IpPort}</c> tuple.</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, Domain, Addr}
</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>Domain</c> is the source transport domain. </p>
</item>
<item>
<p><c>Addr</c> is the source address. </p>
</item>
</list>
<pre>
Server ! {snmp_trap, Trap, Domain, Addr}
</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>Domain</c> is the source transport domain. </p>
</item>
<item>
<p><c>Addr</c> is the source address. </p>
</item>
</list>
<pre>
Server ! {snmp_inform, Ref, Pdu, PduMS, Domain, Addr}
</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>Domain</c> is the source transport domain. </p>
</item>
<item>
<p><c>Addr</c> is the source address. </p>
</item>
</list>
<pre>
Server ! {snmp_report, Data, Domain, Addr}
</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>Domain</c> is the source transport domain. </p>
</item>
<item>
<p><c>Addr</c> is the source address. </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>
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