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<h1>13 Definition of Manager Net if</h1>
<p></p>
<img alt="IMAGE MISSING" src="snmp_manager_netif_1.gif"><br>
<em>Figure
13.1:
The Purpose of Manager Net if</em>
<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,
<span class="code">snmpm_net_if</span> (the default) and <span class="code">snmpm_net_if_mt</span>,
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>
<h3><a name="id85574">13.1
Mandatory Functions</a></h3>
<a name="mandatory_functions"></a>
<p>A Net if process must implement the SNMP manager
<span class="bold_code"><a href="snmpm_network_interface.html">network interface behaviour</a></span>. </p>
<h3><a name="id85591">13.2
Messages</a></h3>
<p>The section <strong>Messages</strong> 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>
<div class="example"><pre>
Server ! {snmp_pdu, Pdu, Addr, Port}
</pre></div>
<ul>
<li>
<p><span class="code">Pdu</span> is an SNMP PDU record, as defined in
<span class="code">snmp_types.hrl</span>, with the SNMP request.</p>
</li>
<li>
<p><span class="code">Addr</span> is the source address. </p>
</li>
<li>
<p><span class="code">Port</span> is port number of the sender.</p>
</li>
</ul>
<div class="example"><pre>
Server ! {snmp_trap, Trap, Addr, Port}
</pre></div>
<ul>
<li>
<p><span class="code">Trap</span> is either an SNMP pdu record or an trappdu record,
as defined in <span class="code">snmp_types.hrl</span>, with the SNMP request.</p>
</li>
<li>
<p><span class="code">Addr</span> is the source address. </p>
</li>
<li>
<p><span class="code">Port</span> is port number of the sender.</p>
</li>
</ul>
<div class="example"><pre>
Server ! {snmp_inform, Ref, Pdu, PduMS, Addr, Port}
</pre></div>
<ul>
<li>
<p><span class="code">Ref</span> is either the atom <span class="code">ignore</span> or something
that can be used to identify the inform-request (e.g. request-id).
<span class="code">ignore</span> 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
<span class="bold_code"><a href="snmpm_network_interface.html#inform_response">inform_response</a></span>
function). See the
<span class="bold_code"><a href="snmp_app.html">inform request behaviour</a></span>
configuration option for more info.</p>
</li>
<li>
<p><span class="code">Pdu</span> is an SNMP PDU record, as defined in
<span class="code">snmp_types.hrl</span>, with the SNMP request.</p>
</li>
<li>
<p><span class="code">Addr</span> is the source address. </p>
</li>
<li>
<p><span class="code">Port</span> is port number of the sender.</p>
</li>
</ul>
<div class="example"><pre>
Server ! {snmp_report, Data, Addr, Port}
</pre></div>
<ul>
<li>
<p><span class="code">Data</span> is either <span class="code">{ok, Pdu}</span> or
<span class="code">{error, ReqId, ReasonInfo, Pdu}</span>. Which one is used depends
on the return value from the MPD
<span class="bold_code"><a href="snmpm_mpd.html#process_msg">process_msg</a></span> function. If the MsgData is <span class="code">ok</span>,
the first is used, and if it is <span class="code">{error, ReqId, Reason}</span>
the latter is used.</p>
</li>
<li>
<p><span class="code">Pdu</span> is an SNMP PDU record, as defined in
<span class="code">snmp_types.hrl</span>, with the SNMP request.</p>
</li>
<li>
<p><span class="code">ReqId</span> is an integer.</p>
</li>
<li>
<p><span class="code">ReasonInfo</span> is a term().</p>
</li>
<li>
<p><span class="code">Addr</span> is the source address. </p>
</li>
<li>
<p><span class="code">Port</span> is port number of the sender.</p>
</li>
</ul>
<h4>Notes</h4>
<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 <span class="code">snmpm_mpd</span> for this purpose (refer to the
Reference Manual, section <span class="code">snmp</span>, module <span class="code">snmpm_mpd</span>
for more details).
</p>
<p>There are also some useful functions for encoding and
decoding of SNMP messages in the module <span class="code">snmp_pdus</span>.
</p>
</div>
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