NetSNMP::TrapReceiver - 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 --with-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 snmprapd.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).

Subroutines are registered using the NetSNMP::TrapReceiver::register funcion, which takes two arguments. The first is a string describing the notification you want to register for (such as linkUp or MyMIB::MyTrap or .1.3.6.1.4.1.2021....). 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/mytrapd.pl):

  #!/usr/bin/perl

  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]})) {
        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/mytrapd.pl";

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:

  ********** PERL RECEIVED A NOTIFICATION:
  PDU INFO:
    notificationtype               TRAP
    receivedfrom                   127.0.0.1
    version                        1
    errorstatus                    0
    messageid                      0
    community                      mycommunity
    transactionid                  2
    errorindex                     0
    requestid                      765160220
  VARBINDS:
    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

# NETSNMPTRAPD_AUTH_HANDLER # NETSNMPTRAPD_HANDLER_BREAK # NETSNMPTRAPD_HANDLER_FAIL # NETSNMPTRAPD_HANDLER_FINISH # NETSNMPTRAPD_HANDLER_OK # NETSNMPTRAPD_POST_HANDLER # NETSNMPTRAPD_PRE_HANDLER

NetSNMP::OID, NetSNMP::ASN

snmptrapd.conf(5) for configuring the Net-SNMP trap receiver.

snmpd.conf(5) for configuring the Net-SNMP snmp agent for sending traps.

http://www.Net-SNMP.org/

W. Hardaker, <hardaker@users.sourceforge.net>

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.