use SNMP::Multi;

    my $req = SNMP::Multi::VarReq->new (
        nonrepeaters => 1,
        hosts => [ qw/ router1.my.com router2.my.com / ],
        vars  => [ [ 'sysUpTime' ], [ 'ifInOctets' ], [ 'ifOutOctets' ] ],
    );
    die "VarReq: $SNMP::Multi::VarReq::error\n" unless $req;

    my $sm = SNMP::Multi->new (
        Method      => 'bulkwalk',
        MaxSessions => 32,
        PduPacking  => 16,
        Community   => 'public',
        Version     => '2c',
        Timeout     => 5,
        Retries     => 3,
        UseNumeric  => 1,
        # Any additional options for SNMP::Session::new() ...
    )
    or die "$SNMP::Multi::error\n";

    $sm->request($req) or die $sm->error;
    my $resp = $sm->execute() or die "Execute: $SNMP::Multi::error\n";

    print "Got response for ", (join ' ', $resp->hostnames()), "\n";
    for my $host ($resp->hosts()) {

        print "Results for $host: \n";
        for my $result ($host->results()) {
            if ($result->error()) {
                print "Error with $host: ", $result->error(), "\n";
                next;
            }

            print "Values for $host: ", (join ' ', $result->values());
            for my $varlist ($result->varlists()) {
                print map { "\t" . $_->fmt() . "\n" } @$varlist;
            }
            print "\n";
        }
    }

Results from all hosts are compiled into a single object, which offers methods to access the data in aggregate, or broken down by host or the individual request.

SNMP::Multi supports SNMP GET, SET, GETNEXT, GETBULK and BULKWALK requests. It also performs PDU packing in order to improve network efficiency, when packing is possible.

METHODS

Building SNMP::Multi::VarReq Requests

The interface to SNMP::Multi::VarReq is very simple, providing only new() and add() methods. They take the following arguments:

    'vars'           => [ list of Varbinds to be requested (REQUIRED) ]
    'hosts'          => [ list of hosts for this variable list ]
    'nonrepeaters'   => [ GETBULK/BULKWALK "nonrepeaters" parameter ]
    'maxrepetitions' => [ GETBULK/BULKWALK "maxrepetitions" parameter ]

Every call to new() or add() must contain a list of SNMP variables. If the hosts parameter is not specified, the variable list will be requested from all hosts currently known by the SNMP::Multi::VarReq object. If a host list is given, the variables will be requested only from the named hosts.

Some simple sanity checks can be performed on the VarReq by calling its validate() method, or by setting $SNMP::Multi::VarReq::autovalidate to 1 before calling the new() method.

An example of building up a complicated request using new() and add():

    Start with:

        $r = SNMP::Multi::VarReq->new(
            hosts => [ qw/ A B C / ],
            vars  => [ qw/ 1 2 3 / ]
        );

    to get:

        A: 1 2 3
        B: 1 2 3
        C: 1 2 3

    Now add a var to each host:

        $r->add( vars => [ qw/ 4 / ] );

    to get:

        A: 1 2 3 4
        B: 1 2 3 4
        C: 1 2 3 4

    Add a var to a specific set of hosts:

        $r->add( hosts => [ qw/ A C / ],
                 vars  => [ qw/ 5   / ] );

    to get:

        A: 1 2 3 4 5
        B: 1 2 3 4
        C: 1 2 3 4 5

    Finally, create two new hosts and add a pair of vars to them:

        $r->add( hosts => [ qw/ D E / ],
                 vars =>  [ qw/ 6 7 / ] );

    to get:

        A: 1 2 3 4 5
        B: 1 2 3 4
        C: 1 2 3 4 5
        D: 6 7
        E: 6 7

The SNMP::Multi::VarReq object also provides a dump() method which generates a simple dump of the current host/var requests.

SNMP PDU Packing Features

For instance, assume your application creates an SNMP::Multi object with a 'PduPacking' value of 3. SNMP::Multi will pack 5 single SNMP variable requests into two distinct requests. The first request will contain the first 3 variables, the second will get the remaining two variables.

PDU packing is not done for SNMP GETBULK and BULKWALK requests. The feature may be disabled by setting the 'PduPacking' parameter to '0'.

Accessing SNMP Data From Agent Responses

This is fairly complicated, but the various objects provide accessor methods to make access to the SNMP responses simple. Assume your application is structured something like this example source code:

    my $req = SNMP::Multi::VarReq->new( hosts => [...],
                                        vars  => [...] );
    my $sm  = SNMP::Multi->new( ... requests => $req, ... );
    my $response = $sm->execute( $overall_timeout );
    die $sm->error() if $sm->error();

Now the data can be accessed through methods on the objects that make up the SNMP::Multi::Response returned by execute(). An SNMP::VarList object is returned for each variable requested. This normalizes the return format across all SNMP operations (including bulkwalks).

See the SYNOPSIS section above for an example of how to access the SNMP data values after calling the execute() method.

CAVEATS

Note that the V1 SNMP protocol has very limited error reporting (the agent returns no values, and the 'errind' is set to the index of the offending SNMP variable request). The SNMP::Multi module adjusts the 'errind' index to indicate which of the variables request requested for a host have failed, regardless of the number of actual packets exchanged. This is necessary to support SNMP::Multi's transparent pdu-packing feature.

SNMP::Multi relies on features added to the SNMP module by Electric Lightwave, Inc. These features have been incorporated into UCD-SNMP releases 4.2 and later. You must have SNMP 4.2 or later installed to use this package.

Using SNMP::Multi with large numbers of hosts or large requests may cause network congestion. All targets may send PDU's to the originating host simultaneously, which could cause heavy traffic and/or dropped packets at the host. Adjusting the Concurrent and PduPacking variables can mitigate this problem.

Network congestion may be a serious problem for bulkwalks, due to multiple packets being exchanged per session. However, network latency and variable target response times cause packets in multiple bulkwalk exchanges to become spread out as the walk progresses. The initial exchange, however, will always cause congestion.

CONTRIBUTORS

Co-maintained by Toni Prug.

This software is provided ``as is'' and without any express or implied warranties, including, without limitation, the implied warranties of merchantibility and/or fitness for a particular purpose.

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