NAME

       snmpm_network_interface_filter  -  Behaviour module for the SNMP manager network-interface
       filter.

DESCRIPTION

       This  module  defines  the  behaviour  of  the  manager  network   interface   filter.   A
       snmpm_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 (snmpm_net_if and snmpm_net_if_mt). The default
       filter accepts all messages.

       A network interface filter can e.g. be used during testing or for load regulation.

       Legacy  network  interface  filter  modules  used   arguments   on   the   form   (IpAddr,
       PortNumber,...)  instead  of  (Domain,  Addr, ...), and if the SNMP manager 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 | trappdu

       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 rejected, 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 rejected, 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 server for primary processing.

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

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

              Types:

                 Domain = transportDomain()
                 Addr = transportAddressWithPort()
                 PduType = pdu_type() > 0

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

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