# global config:
my @interface_names_oid = ( '1.3.6.1.2.1.2.2.1.2' );
my $interface_oid_prefix =  '1.3.6.1.2.1.2.2.1.6';

sub snmp_get($;$)
{
    my( $snmp_sess, $device ) = @_;
    $device ||= 'eth0'; # default

    my $interfaces_table = $snmp_sess->get_entries( -columns => \@interface_names_oid )
        or die $snmp_sess->error;

    $snmp_sess->get_request( -varbindlist => [
        map { join '.', $interface_oid_prefix, /\.(\d+)$/; }
        grep { $interfaces_table->{$_} =~ /$device/ }
        keys %$interfaces_table
    ] )
}