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 UDP 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.

DATA TYPES

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

EXPORTS

       accept_recv(Ip, Port) -> boolean()

              Types:

                 Ip = ip_address()
                 Port = port()

              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(Ip, Port) -> boolean()

              Types:

                 Ip = ip_address()
                 Port = port()

              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(Ip, Port, PduType) -> boolean()

              Types:

                 Ip = ip_address()
                 Port = port()
                 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() = {ip_address(), port()}
                 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  add  its  own)  by
              returning an updated Targets list (NewTargets).

Ericsson AB                                         snmp 4.25               snmpa_network_interface_filter(3erl)