NetSNMP::TrapReceiver(3) Embedded perl trap handling for Net-SNMP's snmptrapd


Put the following lines in your snmptrapd.conf file:

perl NetSNMP::TrapReceiver::register("trapOID", \&myfunc);


The NetSNMP::TrapReceiver module is used to register perl subroutines into the Net-SNMP snmptrapd process. Net-SNMP MUST have been configured using --enable-embedded-perl. Registration of functions is then done through the snmptrapd.conf configuration file. This module can NOT be used in a normal perl script to receive traps. It is intended solely for embedded use within the snmptrapd demon.


Within the snmptrapd.conf file, the keyword ``perl'' may be used to call any perl expression and using this ability, you can use the NetSNMP::TrapReceiver module to register functions which will be called every time a given notification (a trap or an inform) is received. Registered functions are called with 2 arguments. The first is a reference to a hash containing information about how the trap was received (what version of the SNMP protocol was used, where it came from, what SNMP user name or community name it was sent under, etc). The second argument is a reference to an array containing the variable bindings (OID and value information) that define the noification itself. Each variable is itself a reference to an array containing three values: a NetSNMP::OID object, the value that came associated with it, and the value's numeric type (see NetSNMP::ASN for further details on SNMP typing information).

Registered functions should return one of the following values:

Handling the trap succeeded, but lets the snmptrapd demon check for further appropriate handlers.
Handling the trap failed, but lets the snmptrapd demon check for further appropriate handlers.
Stops evaluating the list of handlers for this specific trap, but lets the snmptrapd demon apply global handlers.
Stops searching for further appropriate handlers.

If a handler function does not return anything appropriate or even nothing at all, a return value of NETSNMPTRAPD_HANDLER_OK is assumed.

Subroutines are registered using the NetSNMP::TrapReceiver::register function, which takes two arguments. The first is a string describing the notification you want to register for (such as ``linkUp'' or ``MyMIB::MyTrap'' or ``.''). Two special keywords can be used in place of an OID: ``default'' and ``all''. The ``default'' keyword indicates you want your handler to be called in the case where no other handlers are called. The ``all'' keyword indicates that the handler should ALWAYS be called for every notification.


As an example, put the following code into a file (say ``/usr/local/share/snmp/''):

  sub my_receiver {
      print "********** PERL RECEIVED A NOTIFICATION:\n";
      # print the PDU info (a hash reference)
      print "PDU INFO:\n";
      foreach my $k(keys(%{$_[0]})) {
        if ($k eq "securityEngineID" || $k eq "contextEngineID") {
          printf "  %-30s 0x%s\n", $k, unpack('h*', $_[0]{$k});
        else {
          printf "  %-30s %s\n", $k, $_[0]{$k};
      # print the variable bindings:
      print "VARBINDS:\n";
      foreach my $x (@{$_[1]}) { 
          printf "  %-30s type=%-2d value=%s\n", $x->[0], $x->[2], $x->[1]; 
  NetSNMP::TrapReceiver::register("all", \&my_receiver) || 
    warn "failed to register our perl trap handler\n";
  print STDERR "Loaded the example perl snmptrapd handler\n";

Then, put the following line in your snmprapd.conf file:

  perl do "/usr/local/share/snmp/";

Start snmptrapd (as root, and the following other opions make it stay in the foreground and log to stderr):

  snmptrapd -f -Le

You should see it start up and display the final message from the end of the above perl script:

  Loaded the perl snmptrapd handler
  2004-02-11 10:08:45 NET-SNMP version 5.2 Started.

Then, if you send yourself a fake trap using the following example command:

  snmptrap -v 2c -c mycommunity localhost 0 linkUp ifIndex.1 i 1 \
      ifAdminStatus.1 i up ifOperStatus.1 i up ifDescr s eth0

You should see the following output appear from snmptrapd as your perl code gets executed:

    notificationtype               TRAP
    version                        1
    errorstatus                    0
    messageid                      0
    community                      mycommunity
    transactionid                  2
    errorindex                     0
    requestid                      765160220
    sysUpTimeInstance              type=67 value=0:0:00:00.00
    snmpTrapOID.0                  type=6  value=linkUp
    ifIndex.1                      type=2  value=1
    ifAdminStatus.1                type=2  value=1
    ifOperStatus.1                 type=2  value=1
    ifDescr                        type=4  value="eth0"


None by default.

# =head2 Exportable constants



W. Hardaker, <[email protected]>


Copyright 2004 by W. Hardaker

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.