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  <header>
    <copyright>
      <year>2007</year><year>2020</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.
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      distributed under the License is distributed on an "AS IS" BASIS,
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      See the License for the specific language governing permissions and
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    </legalnotice>

    <title>snmpa_network_interface_filter</title>
    <prepared></prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date></date>
    <rev></rev>
    <file>snmpa_network_interface_filter.xml</file>
  </header>
  <module since="">snmpa_network_interface_filter</module>
  <modulesummary>Behaviour module for the SNMP agent network-interface filter.</modulesummary>
  <description>
    <p>This module defines the behaviour of the agent network interface
      filter. A <c>snmpa_network_interface_filter</c> compliant module 
      must export the following functions: </p>
    <list type="bulleted">
      <item>
        <p><seeerl marker="#accept_recv">accept_recv/2</seeerl></p>
      </item>
      <item>
        <p><seeerl marker="#accept_send">accept_send/2</seeerl></p>
      </item>
      <item>
        <p><seeerl marker="#accept_recv_pdu">accept_recv_pdu/3</seeerl></p>
      </item>
      <item>
        <p><seeerl marker="#accept_send_pdu">accept_send_pdu/2</seeerl></p>
      </item>
    </list>
    <p>The semantics of them and their exact signatures are explained
      below. </p>
    <p>The purpose of the network interface filter is to allow for filtering
      of messages (accept or reject) receive and send. This is done 
      on two levels: </p>
    <list type="bulleted">
      <item>
        <p>The first level is at the transport entry / exit point, i.e.
          immediately after the receipt of the message before any message
          processing is done (accept_recv) and 
          immediately before sending the message after all message
          processing is done (accept_send).</p>
      </item>
      <item>
        <p>The second level is at the MPD entry / exit point, i.e.
          immediately after the basic message processing (accept_recv_pdu) / 
          immediately before the basic message processing (accept_send_pdu).</p>
      </item>
    </list>
    <p>Note that the network interface filter is something which is used 
      by the network interface implementation provided by the application 
      (<c>snmpa_net_if</c>). The default filter accepts all messages.</p>
    <p>A network interface filter can e.g. be used during testing or for load 
      regulation. If the intended use is load regulation, see also 
      <seeguide marker="snmp_config#agent_ni_req_limit">req_limit</seeguide> and 
      the function 
      <seeerl marker="snmpa#register_notification_filter">register_notification_filter</seeerl>. </p>
    <p>Legacy network interface filter modules used arguments on the form
      <c>(IpAddr, PortNumber,...)</c> instead of
      <c>(Domain, Addr, ...)</c>, and if the SNMP agent is run without
      changing the configuration to use transport domains
      the network interface filter will still get
      the old arguments and work as before.</p>
  </description>

  <section>
    <title>DATA TYPES</title>
    <code type="none">
port() = integer() > 0
pdu_type() = 'get-request' | 'get-next-request' | 'get-response' | 
             'set-request' | trap | 'get-bulk-request' | 'inform-request' | 
             report
    </code>
    <p>See also the <seeerl marker="snmpa_conf#types">
    data types in <c>snmpa_conf</c></seeerl>.</p>
    <marker id="accept_recv"></marker>
  </section>
  <funcs>
    <func>
      <name since="">accept_recv(Domain, Addr) -> boolean()</name>
      <fsummary>Shall the received message be accepted</fsummary>
      <type>
	<v>Domain = transportDomain()</v>
	<v>Addr = transportAddressWithPort()</v>
      </type>
      <desc>
        <p>Called at the reception of a message (before <em>any</em> processing 
          has been done).</p>
        <p>For the message to be discarded, the function <em>must</em> return
          <em>false</em>. </p>
        <marker id="accept_send"></marker>
      </desc>
    </func>
    <func>
      <name since="">accept_send(Domain, Addr) -> boolean()</name>
      <fsummary>Shall the message be sent</fsummary>
      <type>
	<v>Domain = transportDomain()</v>
	<v>Addr = transportAddressWithPort()</v>
      </type>
      <desc>
        <p>Called before the sending of a message (after <em>all</em> processing 
          has been done).</p>
        <p>For the message to be discarded, the function <em>must</em> return
          <em>false</em>. </p>
        <marker id="accept_recv_pdu"></marker>
      </desc>
    </func>
    <func>
      <name since="">accept_recv_pdu(Domain, Addr, PduType) -> boolean()</name>
      <fsummary>Shall the received pdu be accepted</fsummary>
      <type>
	<v>Domain = transportDomain()</v>
	<v>Addr = transportAddressWithPort()</v>
        <v>PduType = pdu_type()</v>
      </type>
      <desc>
        <p>Called after the basic message processing (MPD) has been done, 
          but before the pdu is handed over to the master-agent for 
          primary processing.</p>
        <p>For the pdu to be discarded, the function <em>must</em> return
          <em>false</em>. </p>
        <marker id="accept_send_pdu"></marker>
      </desc>
    </func>
    <func>
      <name since="">accept_send_pdu(Targets, PduType) -> Reply</name>
      <fsummary>Shall the pdu be sent</fsummary>
      <type>
        <v>Targets = targets()</v>
        <v>targets() = [target()]</v>
        <v>target() = {Domain, Addr}</v>
	<v>Domain = transportDomain()</v>
	<v>Addr = transportAddressWithPort()</v>
        <v>PduType = pdu_type() > 0</v>
        <v>Reply = boolean() | NewTargets</v>
        <v>NewTargets = targets()</v>
      </type>
      <desc>
        <p>Called before the basic message processing (MPD) is done, 
          when a pdu has been received from the master-agent.</p>
        <p>For the message to be discarded all together, the function 
          <em>must</em> return <em>false</em>. </p>
        <p>Note that it is possible for this function to filter out targets
          (but <em>not</em> to add its own) by returning an updated
          <c>Targets</c> list (<c>NewTargets</c>). </p>
      </desc>
    </func>
  </funcs>
  
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