LLC(3) User Contributed Perl Documentation LLC(3)NAME
"NetPacket::LLC" - Assemble and disassemble IEEE 802.3 LLC protocol
packets.
SYNOPSIS
use NetPacket::LLC;
use NetPacket::SpanningTree;
$llc_data = NetPacket::Ethernet->strip($raw_packet);
$st_data = NetPacket::LLC->strip($llc_data);
$st_obj = NetPacket::SpanningTree->decode($st_data);
DESCRIPTION
"NetPacket::LLC" provides a set of routines for assembling and
disassembling packets using the IEEE standard LLC protocol layer.
Methods
"NetPacket::LLC->decode([ST DATA])"
Decode the LLC packet data and return an object containing instance
data. This method will probably decode garbage input, but it won't
mean much.
"NetPacket::SpanningTree->encode($st_hash)"
Encode the hash into a raw data stream that may be appended to
ethernet packet data. This allows the user to create his/her own
LLC protocol packet and subsequently send it out on the wire
(though sending on the wire isn't a function of this module).
Functions
"NetPacket::LLC->strip([LLC DATA])"
Strip the LLC data from the packet, and return any underlying data.
Instance data
The instance data contains in the hash returned by the encode and
decode methodsof the "NetPacket::LLC" module contain the following
fields. Note, please refer to the IEEE spec for a description of these
fields. They are not described in detail here unless relevant to
encoding.
max_age
message_age
bpdu_flags
bridge_id
Exports
exportable
llc_strip
tags
The following tags group together related exportable items.
":strip"
Import the strip function "st_strip"
":ALL"
All the above exportable items
EXAMPLE
The following is a script that listens on device "eth1" for spanning
tree packets. It then decodes the packets, re-encodes them, and
verifies that the both the original and re-encoded data are identical.
It uses tLLC module to decode the LLC layer.
#!/usr/bin/perl -w # # Perl script to verify that Spanning Tree packet
intervals are correct # # #
use strict; use Net::PcapUtils; use NetPacket::Ethernet; use
NetPacket::LLC; use NetPacket::SpanningTree;
{
my $iface = "eth1";
my $errmsg = Net::PcapUtils::loop(\&process_pkt,
DEV => $iface );
if (defined $errmsg) { die "$errmsg\n"; } }
sub process_pkt {
my ($arg, $hdr, $pkt) = @_;
my $eth_obj = NetPacket::Ethernet->decode($pkt);
if ((defined $eth_obj->{length}) &&
($eth_obj->{dest_mac} =~ m/^0180c200000/)) { # Spanning Tree protocol
my $llc_obj = NetPacket::LLC->decode($eth_obj->{data});
my $st_obj = NetPacket::SpanningTree->decode($llc_obj->{data});
verifyEncoding($st_obj);
my $newdata = NetPacket::SpanningTree->encode($st_obj);
return;
}
}
# # Decode a packet and compare it to a hash of data to be encoded. #
# Input is a hash of data to be encoded. The subroutine encodes and #
subsequently decodes the data and verifies the data matches. #
sub verifyEncoding {
my ($st_obj) = @_;
my $newdata =
NetPacket::SpanningTree->encode($st_obj);
my $st_obj1 =
NetPacket::SpanningTree->decode($newdata);
foreach my $key (keys %$st_obj) {
if ($key =~ m/data/i) { next; }
if ($key =~ m/frame/i) { next; }
if ($key =~ m/_parent/i) { next; }
if ($st_obj->{$key} eq $st_obj1->{$key}) {
print "$key is identical ($st_obj1->{$key})\n";
} else {
print
"$key is $st_obj->{$key} before $st_obj1->{$key}
after\n";
}
}
}
TODO
Better documentation
Clean up some code.
SEE ALSO
"NetPacket::LLC"
Module to decode LLC packets (Logical Link Control)
"NetPacket::Ethernet"
Module to decode Ethernet Packets
"Net::RawIP"
Module to send encoded data out.
"Net::PcapUtils"
Utility module to be used for packet capture.
COPYRIGHT
Copyright (c) 2002 Chander Ganesan.
This package is free software and is provided "as is" without express
or implied warranty. It may be used, redistributed and/or modified
under the terms of the Perl Artistic License (see
http://www.perl.com/perl/misc/Artistic.html)
This software and all associated data and documentation ('Software') is
available free of charge. You may make copies of the Software but you
must include all of this notice on any copy.
The Software was developed for research purposes does not warrant that
it is error free or fit for any purpose. The author disclaims any
liability for all claims, expenses, losses, damages and costs any user
may incur as a result of using, copying or modifying the Software.
AUTHOR
Chander Ganesan <cganesan@cpan.org<gt>
perl v5.14.0 2003-01-29 LLC(3)
