"NetPacket::SpanningTree" - Assemble and disassemble IEEE 802.1D Spanning Tree protocol packets. 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); "NetPacket::SpanningTree" provides a set of routines for assembling and disassembling packets using the IEEE standard Spanning Tree Protocol. Spanning Tree is a layer 2 protocol defined by the IEEE 802.1D specification.

Methods
Decode the spanning tree packet data and return an object containing instance data. This method will probably decode garbage input, but it won't mean much. Encode the hash into a raw data stream that may be appended to LLC data, then to an ethernet packet. This allows the user to create his/her own Spanning Tree protocol packet and subsequently send it out on the wire (though sending on the wire isn't a function of this application).

Functions
Strip the spanning tree data from the packet, and return any underlying data. This returns undef since there is no "data" per say included in the spanning tree packet.

Instance data
The instance data contains in the hash returned by the encode and decode methodsof the "NetPacket::SpanningTree" 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. When available, values not suppiled will be set to IEEE 802.1D defaults. A single octet, representing the topology change flag (TC) (LSB) and the topology change notification acknowledgement (TCA) (MSB). This parameter is contructed when encoding, please refer to the TC and TCA items to set the appropriate bits. This (along with bridge_priority) is used to build the bridge_id when encoding. This (along with bridge_mac) is used to build the bridge_id when encoding. This value should always be 0, defaults to 0. Note, this value also contains the message type (which is also always 0). This (along with root_mac) is used to build the root_id when encoding. This value should always be 0, defaults to 0. This (along with root_priority) is used to build the root_id when encoding. This (along with port_num) is used to build the port_id when encoding.

Exports
st_strip The following tags group together related exportable items. Import the strip function "st_strip" All the above exportable items 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. #!/usr/bin/perl -w # # Perl script to verify that LACP 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"; } } } Module to decode LLC packets (Logical Link Control) Module to decode Ethernet Packets Module to send encoded data out. Utility module to be used for packet capture. 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. Chander Ganesan <cganesan@cpan.org<gt>