.TH snmpa_network_interface_filter 3erl "snmp 5.2.4" "Ericsson AB" "Erlang Module Definition"
.SH NAME
snmpa_network_interface_filter \- Behaviour module for the SNMP agent network-interface filter.
.SH DESCRIPTION
.LP
This module defines the behaviour of the agent network interface filter\&. A \fIsnmpa_network_interface_filter\fR\& compliant module must export the following functions:
.RS 2
.TP 2
*
\fBaccept_recv/2\fR\&
.LP
.TP 2
*
\fBaccept_send/2\fR\&
.LP
.TP 2
*
\fBaccept_recv_pdu/3\fR\&
.LP
.TP 2
*
\fBaccept_send_pdu/2\fR\&
.LP
.RE

.LP
The semantics of them and their exact signatures are explained below\&.
.LP
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:
.RS 2
.TP 2
*
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)\&.
.LP
.TP 2
*
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)\&.
.LP
.RE

.LP
Note that the network interface filter is something which is used by the network interface implementation provided by the application (\fIsnmpa_net_if\fR\&)\&. The default filter accepts all messages\&.
.LP
A network interface filter can e\&.g\&. be used during testing or for load regulation\&. If the intended use is load regulation, see also \fBreq_limit\fR\& and the function \fBregister_notification_filter\fR\&\&.
.LP
Legacy network interface filter modules used arguments on the form \fI(IpAddr, PortNumber,\&.\&.\&.)\fR\& instead of \fI(Domain, Addr, \&.\&.\&.)\fR\&, 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\&.
.SH "DATA TYPES"

.LP
.nf

port() = integer() > 0
pdu_type() = 'get-request' | 'get-next-request' | 'get-response' | 
             'set-request' | trap | 'get-bulk-request' | 'inform-request' | 
             report
    
.fi
.LP
See also the \fB data types in \fIsnmpa_conf\fR\&\fR\&\&.
.SH EXPORTS
.LP
.B
accept_recv(Domain, Addr) -> boolean()
.br
.RS
.LP
Types:

.RS 3
Domain = transportDomain()
.br
Addr = transportAddressWithPort()
.br
.RE
.RE
.RS
.LP
Called at the reception of a message (before \fIany\fR\& processing has been done)\&.
.LP
For the message to be discarded, the function \fImust\fR\& return \fIfalse\fR\&\&.
.RE

.LP
.B
accept_send(Domain, Addr) -> boolean()
.br
.RS
.LP
Types:

.RS 3
Domain = transportDomain()
.br
Addr = transportAddressWithPort()
.br
.RE
.RE
.RS
.LP
Called before the sending of a message (after \fIall\fR\& processing has been done)\&.
.LP
For the message to be discarded, the function \fImust\fR\& return \fIfalse\fR\&\&.
.RE

.LP
.B
accept_recv_pdu(Domain, Addr, PduType) -> boolean()
.br
.RS
.LP
Types:

.RS 3
Domain = transportDomain()
.br
Addr = transportAddressWithPort()
.br
PduType = pdu_type()
.br
.RE
.RE
.RS
.LP
Called after the basic message processing (MPD) has been done, but before the pdu is handed over to the master-agent for primary processing\&.
.LP
For the pdu to be discarded, the function \fImust\fR\& return \fIfalse\fR\&\&.
.RE

.LP
.B
accept_send_pdu(Targets, PduType) -> Reply
.br
.RS
.LP
Types:

.RS 3
Targets = targets()
.br
targets() = [target()]
.br
target() = {Domain, Addr}
.br
Domain = transportDomain()
.br
Addr = transportAddressWithPort()
.br
PduType = pdu_type() > 0
.br
Reply = boolean() | NewTargets
.br
NewTargets = targets()
.br
.RE
.RE
.RS
.LP
Called before the basic message processing (MPD) is done, when a pdu has been received from the master-agent\&.
.LP
For the message to be discarded all together, the function \fImust\fR\& return \fIfalse\fR\&\&.
.LP
Note that it is possible for this function to filter out targets (but \fInot\fR\& to add its own) by returning an updated \fITargets\fR\& list (\fINewTargets\fR\&)\&.
.RE