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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<TITLE>Definition of Manager Net if</TITLE>
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<A NAME="13"><!-- Empty --></A>
<H2>13 Definition of Manager Net if</H2>
<P>
<P>
<CENTER>
<IMG ALT="snmp_manager_netif_1" SRC="snmp_manager_netif_1.gif"><BR>
<EM>The Purpose of Manager Net if</EM>
</CENTER>
<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>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>It is also possible to write your own Net if process. The default
Net if process is implemented in the module <CODE>snmpm_net_if</CODE> and
it uses UDP as the transport protocol.
<P>This section describes how to write a Net if process.
<A NAME="mandatory_functions"><!-- Empty --></A><A NAME="13.1"><!-- Empty --></A>
<H3>13.1 Mandatory Functions</H3>
<P>A Net if process must implement the SNMP manager
<A HREF="snmpm_network_interface.html">network interface behaviour</A>.
<A NAME="13.2"><!-- Empty --></A>
<H3>13.2 Messages</H3>
<P>The section <STRONG>Messages</STRONG> describes mandatory messages, which
Net if must send to the manager server process.
<P>Net if must send the following message when it receives an
SNMP PDU from the network that is aimed for the MasterAgent:
<PRE>
Server ! {snmp_pdu, Pdu, Addr, Port}
</PRE>
<P>
<UL>
<LI>
<CODE>Pdu</CODE> is an SNMP PDU record, as defined in
<CODE>snmp_types.hrl</CODE>, with the SNMP request.
<BR>
</LI>
<LI>
<CODE>Addr</CODE> is the source address.
<BR>
</LI>
<LI>
<CODE>Port</CODE> is port number of the sender.
<BR>
</LI>
</UL>
<PRE>
Server ! {snmp_trap, Trap, Addr, Port}
</PRE>
<P>
<UL>
<LI>
<CODE>Trap</CODE> is aither an SNMP pdu record or an trappdu record,
as defined in <CODE>snmp_types.hrl</CODE>, with the SNMP request.
<BR>
</LI>
<LI>
<CODE>Addr</CODE> is the source address.
<BR>
</LI>
<LI>
<CODE>Port</CODE> is port number of the sender.
<BR>
</LI>
</UL>
<PRE>
Server ! {snmp_inform, Ref, Pdu, PduMS, Addr, Port}
</PRE>
<P>
<UL>
<LI>
<CODE>Ref</CODE> is either the atom <CODE>ignore</CODE> or something
that can be used to identify the inform-request (e.g. request-id).
<CODE>ignore</CODE> is used if the response (acknowledgement) to the
inform-request has already been sent (this means that the server
will not make the call to the
<A HREF="snmpm_network_interface.html#inform_response">inform_response</A>
function). See the
<A HREF="snmp_app.html">inform request behaviour</A>
configuration option for more info.
<BR>
</LI>
<LI>
<CODE>Pdu</CODE> is an SNMP PDU record, as defined in
<CODE>snmp_types.hrl</CODE>, with the SNMP request.
<BR>
</LI>
<LI>
<CODE>Addr</CODE> is the source address.
<BR>
</LI>
<LI>
<CODE>Port</CODE> is port number of the sender.
<BR>
</LI>
</UL>
<PRE>
Server ! {snmp_report, Data, Addr, Port}
</PRE>
<P>
<UL>
<LI>
<CODE>Data</CODE> is either <CODE>{ok, Pdu}</CODE> or
<CODE>{error, ReqId, ReasonInfo, Pdu}</CODE>. Which one is used depends
on the return value from the MPD
<A HREF="snmpm_mpd.html#process_msg"> process_msg</A> function. If the MsgData is <CODE>ok</CODE>,
the first is used, and if it is <CODE>{error, ReqId, Reason}</CODE>
the latter is used.
<BR>
</LI>
<LI>
<CODE>Pdu</CODE> is an SNMP PDU record, as defined in
<CODE>snmp_types.hrl</CODE>, with the SNMP request.
<BR>
</LI>
<LI>
<CODE>ReqId</CODE> is an integer.
<BR>
</LI>
<LI>
<CODE>ReasonInfo</CODE> is a term().
<BR>
</LI>
<LI>
<CODE>Addr</CODE> is the source address.
<BR>
</LI>
<LI>
<CODE>Port</CODE> is port number of the sender.
<BR>
</LI>
</UL>
<A NAME="13.2.1"><!-- Empty --></A>
<H4>13.2.1 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 <CODE>snmpm_mpd</CODE> for this purpose (refer to the
Reference Manual, section <CODE>snmp</CODE>, module <CODE>snmpm_mpd</CODE>
for more details).
<P>There are also some useful functions for encoding and
decoding of SNMP messages in the module <CODE>snmp_pdus</CODE>.
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