snmpa_network_interface_filter(3)



snmpa_network_interface_filErlangrModule Dsnmpa_network_interface_filter(3erl)

NAME
       snmpa_network_interface_filter  -  Behaviour  module for the SNMP agent
       network-interface filter.

DESCRIPTION
       This module defines the behaviour of the agent network  interface  fil-
       ter.  A snmpa_network_interface_filter compliant module must export the
       following functions:

         * accept_recv/2

         * accept_send/2

         * accept_recv_pdu/3

         * accept_send_pdu/2

       The semantics of them and their exact signatures are explained below.

       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:

         * The first level is at the transport entry / exit point, i.e.  imme-
           diately  after  the  receipt of the message before any message pro-
           cessing is done (accept_recv) and immediately  before  sending  the
           message after all message processing is done (accept_send).

         * 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).

       Note  that  the  network interface filter is something which is used by
       the network interface implementation provided by the  application  (sn-
       mpa_net_if). The default filter accepts all messages.

       A  network interface filter can e.g. be used during testing or for load
       regulation. If the intended use is load regulation, see also  req_limit
       and the function register_notification_filter.

       Legacy  network  interface  filter  modules  used arguments on the form
       (IpAddr, PortNumber,...) instead of (Domain, Addr,  ...),  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.

DATA TYPES
       port() = integer() > 0
       pdu_type() = 'get-request' | 'get-next-request' | 'get-response' |
                    'set-request' | trap | 'get-bulk-request' | 'inform-request' |
                    report

       See also the  data types in snmpa_conf.

EXPORTS
       accept_recv(Domain, Addr) -> boolean()

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()

              Called  at the reception of a message (before any processing has
              been done).

              For the message to be discarded, the function must return false.

       accept_send(Domain, Addr) -> boolean()

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()

              Called before the sending of a message (after all processing has
              been done).

              For the message to be discarded, the function must return false.

       accept_recv_pdu(Domain, Addr, PduType) -> boolean()

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()
                 PduType = pdu_type()

              Called  after  the basic message processing (MPD) has been done,
              but before the pdu is handed over to the master-agent  for  pri-
              mary processing.

              For the pdu to be discarded, the function must return false.

       accept_send_pdu(Targets, PduType) -> Reply

              Types:

                 Targets = targets()
                 targets() = [target()]
                 target() = {Domain, Addr}
                 Domain = transportDomain()
                 Addr = transportAddressWithPort()
                 PduType = pdu_type() > 0
                 Reply = boolean() | NewTargets
                 NewTargets = targets()

              Called before the basic message processing (MPD) is done, when a
              pdu has been received from the master-agent.

              For the message to be discarded all together, the function  must
              return false.

              Note that it is possible for this function to filter out targets
              (but not to add its own) by returning an  updated  Targets  list
              (NewTargets).

Ericsson AB                        snmp 5.snmpa_network_interface_filter(3erl)

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