NetPacket::LLC(3pm)

1LLC(3)                User Contributed Perl Documentation               LLC(3)
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NAME

6       "NetPacket::LLC" - Assemble and disassemble IEEE 802.3 LLC protocol
7       packets.
8

SYNOPSIS

10        use NetPacket::LLC;
11        use NetPacket::SpanningTree;
12
13        $llc_data = NetPacket::Ethernet->strip($raw_packet);
14        $st_data = NetPacket::LLC->strip($llc_data);
15        $st_obj = NetPacket::SpanningTree->decode($st_data);
16

DESCRIPTION

18       "NetPacket::LLC" provides a set of routines for assembling and
19       disassembling packets using the IEEE standard LLC protocol layer.
20
21   Methods
22       "NetPacket::LLC->decode([ST DATA])"
23           Decode the LLC packet data and return an object containing instance
24           data.  This method will probably decode garbage input, but it won't
25           mean much.
26
27       "NetPacket::SpanningTree->encode($st_hash)"
28           Encode the hash into a raw data stream that may be appended to
29           ethernet packet data.  This allows the user to create his/her own
30           LLC protocol packet and subsequently send it out on the wire
31           (though sending on the wire isn't a function of this module).
32
33   Functions
34       "NetPacket::LLC->strip([LLC DATA])"
35           Strip the LLC data from the packet, and return any underlying data.
36
37   Instance data
38       The instance data contains in the hash returned by the encode and
39       decode methodsof the "NetPacket::LLC" module contain the following
40       fields.  Note, please refer to the IEEE spec for a description of these
41       fields.  They are not described in detail here unless relevant to
42       encoding.
43
44       max_age
45       message_age
46       bpdu_flags
47       bridge_id
48
49   Exports
50       exportable
51           llc_strip
52
53       tags
54           The following tags group together related exportable items.
55
56           ":strip"
57               Import the strip function "st_strip"
58
59           ":ALL"
60               All the above exportable items
61

EXAMPLE

63       The following is a script that listens on device "eth1" for spanning
64       tree packets.  It then decodes the packets, re-encodes them, and
65       verifies that the both the original and re-encoded data are identical.
66       It uses tLLC module to decode the LLC layer.
67
68       #!/usr/bin/perl -w # # Perl script to verify that Spanning Tree packet
69       intervals are correct # # #
70
71       use strict; use Net::PcapUtils; use NetPacket::Ethernet; use
72       NetPacket::LLC; use NetPacket::SpanningTree;
73
74       {
75           my $iface = "eth1";
76           my $errmsg = Net::PcapUtils::loop(\&process_pkt,
77                                             DEV => $iface );
78           if (defined $errmsg) { die "$errmsg\n"; } }
79
80       sub process_pkt {
81           my ($arg, $hdr, $pkt)  = @_;
82           my $eth_obj = NetPacket::Ethernet->decode($pkt);
83
84           if ((defined $eth_obj->{length}) &&
85               ($eth_obj->{dest_mac} =~ m/^0180c200000/)) { # Spanning Tree protocol
86               my $llc_obj = NetPacket::LLC->decode($eth_obj->{data});
87               my $st_obj = NetPacket::SpanningTree->decode($llc_obj->{data});
88               verifyEncoding($st_obj);
89
90               my $newdata = NetPacket::SpanningTree->encode($st_obj);
91               return;
92           }
93        }
94
95       # # Decode a packet and compare it to a hash of data to be encoded.  #
96       # Input is a hash of data to be encoded.  The subroutine encodes and #
97       subsequently decodes the data and verifies the data matches.  #
98
99       sub verifyEncoding {
100           my ($st_obj) = @_;
101           my $newdata =
102               NetPacket::SpanningTree->encode($st_obj);
103           my $st_obj1 =
104               NetPacket::SpanningTree->decode($newdata);
105           foreach my $key (keys %$st_obj) {
106               if ($key =~ m/data/i) { next; }
107               if ($key =~ m/frame/i) { next; }
108               if ($key =~ m/_parent/i) { next; }
109               if ($st_obj->{$key} eq $st_obj1->{$key}) {
110                   print "$key is identical ($st_obj1->{$key})\n";
111               } else {
112                   print
113                       "$key is $st_obj->{$key} before $st_obj1->{$key}
114       after\n";
115               }
116           }
117        }
118

TODO

120       Better documentation
121       Clean up some code.
122

COPYRIGHT

137       Copyright (c) 2002 Chander Ganesan.
138
139       This package is free software and is provided "as is" without express
140       or implied warranty.  It may be used, redistributed and/or modified
141       under the terms of the Perl Artistic License (see
142       http://www.perl.com/perl/misc/Artistic.html)
143
144       This software and all associated data and documentation ('Software') is
145       available free of charge.  You may make copies of the Software but you
146       must include all of this notice on any copy.
147
148       The Software was developed for research purposes does not warrant that
149       it is error free or fit for any purpose.  The author disclaims any
150       liability for all claims, expenses, losses, damages and costs any user
151       may incur as a result of using, copying or modifying the Software.
152

AUTHOR

154       Chander Ganesan <cganesan@cpan.org<gt>
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158perl v5.12.3                      2003-01-29                            LLC(3)