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 filter. 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. 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).

         * 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 (snmpa_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 primary 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 5.13.5              snmpa_network_interface_filter(3erl)