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<chapter>
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    <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>{</c><seealso marker="kernel:inet#type-ip_address"><c>IpAddr</c></seealso><c>,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>

