I use the following in a script I run to get a list of interfaces from Cisco... (perhaps the leading "." on your varbind is the culprit? - or not...)

...

use strict;
use Net::SNMP;

...

sub get_if_ids
{
    my ( $hostname ) = @_;
    my %ifs;
    my $ifEntry = "1.3.6.1.2.1.2.2.1.2";

    my ( $session, $error ) = Net::SNMP->session(
        -hostname  => $hostname,
        -version   => 1,
        -community => "public" );

    if ( !defined( $session ) )
    {
        print "ERROR: SNMP - $error\n";
        return undef;
    }

    my $result = $session->get_next_request( -varbindlist => [$ifEntry
+] );

    while ( defined( $result ) )
    {
        foreach my $key ( keys %$result )
        {
            if (  $key !~ /^$ifEntry/ )
            {
                $result = undef;
                last;
            }

            #  process $result...
            #  Update:  $key is 1.3.6.1.2.1.2.2.1.2.n for the nth inte
+rface
            #           $result->{$key} is interface name

            $result = $session->get_next_request( -varbindlist => [$ke
+y] );
        }
    }

    $session->close();

    return \%ifs;
}
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