1SpanningTree(3) User Contributed Perl Documentation SpanningTree(3)
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6 "NetPacket::SpanningTree" - Assemble and disassemble IEEE 802.1D
7 Spanning Tree protocol packets.
8
10 use NetPacket::LLC;
11 use NetPacket::SpanningTree;
12 $llc_data = NetPacket::Ethernet->strip($raw_packet);
14 $st_data = NetPacket::LLC->strip($llc_data);
15 $st_obj = NetPacket::SpanningTree->decode($st_data);
16
18 "NetPacket::SpanningTree" provides a set of routines for assembling and
19 disassembling packets using the IEEE standard Spanning Tree Protocol.
20 Spanning Tree is a layer 2 protocol defined by the IEEE 802.1D
21 specification.
22 Methods
24 "NetPacket::SpanningTree->decode([ST DATA])"
25 Decode the spanning tree packet data and return an object
26 containing instance data. This method will probably decode garbage
27 input, but it won't mean much.
28 "NetPacket::SpanningTree->encode($st_hash)"
30 Encode the hash into a raw data stream that may be appended to LLC
31 data, then to an ethernet packet. This allows the user to create
32 his/her own Spanning Tree protocol packet and subsequently send it
33 out on the wire (though sending on the wire isn't a function of
34 this application).
35 Functions
37 "NetPacket::SpanningTree->strip([ST DATA])"
38 Strip the spanning tree data from the packet, and return any
39 underlying data. This returns undef since there is no "data" per
40 say included in the spanning tree packet.
41 Instance data
43 The instance data contains in the hash returned by the encode and
44 decode methodsof the "NetPacket::SpanningTree" module contain the
45 following fields. Note, please refer to the IEEE spec for a
46 description of these fields. They are not described in detail here
47 unless relevant to encoding. When available, values not suppiled will
48 be set to IEEE 802.1D defaults.
49 max_age
51 message_age
52 bpdu_flags
53 A single octet, representing the topology change flag (TC) (LSB) and the
54 topology change notification acknowledgement (TCA) (MSB). This parameter
55 is contructed when encoding, please refer to the TC and TCA items to set
56 the appropriate bits.
57 bridge_mac
59 This (along with bridge_priority) is used to build the bridge_id when encoding.
60 bpdu_type
62 topology_change
63 bridge_priority
64 This (along with bridge_mac) is used to build the bridge_id when encoding.
65 topology_change_ack
67 protocol_version
68 This value should always be 0, defaults to 0. Note, this value also
69 contains the message type (which is also always 0).
70 forward_delay
72 hello_time
73 port_num
74 root_priority
75 This (along with root_mac) is used to build the root_id when encoding.
76 root_path_cost
78 protocol_id
79 This value should always be 0, defaults to 0.
80 root_mac
82 This (along with root_priority) is used to build the root_id when encoding.
83 port_priority
85 This (along with port_num) is used to build the port_id when encoding.
86 root_id
88 port_id
89 bridge_id
90 Exports
92 exportable
93 st_strip
94 tags
96 The following tags group together related exportable items.
97 ":strip"
99 Import the strip function "st_strip"
100 ":ALL"
102 All the above exportable items
103
105 The following is a script that listens on device "eth1" for spanning
106 tree packets. It then decodes the packets, re-encodes them, and
107 verifies that the both the original and re-encoded data are identical.
108 #!/usr/bin/perl -w # # Perl script to verify that LACP packet intervals
110 are correct # # #
111 use strict; use Net::PcapUtils; use NetPacket::Ethernet; use
113 NetPacket::LLC; use NetPacket::SpanningTree;
114 {
116 my $iface = "eth1";
117 my $errmsg = Net::PcapUtils::loop(\&process_pkt,
118 DEV => $iface );
119 if (defined $errmsg) { die "$errmsg\n"; } }
120 sub process_pkt {
122 my ($arg, $hdr, $pkt) = @_;
123 my $eth_obj = NetPacket::Ethernet->decode($pkt);
124 if ((defined $eth_obj->{length}) &&
126 ($eth_obj->{dest_mac} =~ m/^0180c200000/)) { # Spanning Tree protocol
127 my $llc_obj = NetPacket::LLC->decode($eth_obj->{data});
128 my $st_obj = NetPacket::SpanningTree->decode($llc_obj->{data});
129 verifyEncoding($st_obj);
130 my $newdata = NetPacket::SpanningTree->encode($st_obj);
132 return;
133 }
134 }
135 # # Decode a packet and compare it to a hash of data to be encoded. #
137 # Input is a hash of data to be encoded. The subroutine encodes and #
138 subsequently decodes the data and verifies the data matches. #
139 sub verifyEncoding {
141 my ($st_obj) = @_;
142 my $newdata =
143 NetPacket::SpanningTree->encode($st_obj);
144 my $st_obj1 =
145 NetPacket::SpanningTree->decode($newdata);
146 foreach my $key (keys %$st_obj) {
147 if ($key =~ m/data/i) { next; }
148 if ($key =~ m/frame/i) { next; }
149 if ($key =~ m/_parent/i) { next; }
150 if ($st_obj->{$key} eq $st_obj1->{$key}) {
151 print "$key is identical ($st_obj1->{$key})\n";
152 } else {
153 print
154 "$key is $st_obj->{$key} before $st_obj1->{$key}
155 after\n";
156 }
157 }
158 }
159
161 Better documentation
162 Clean up some code.
163
165 "NetPacket::LLC"
166 Module to decode LLC packets (Logical Link Control)
167 "NetPacket::Ethernet"
169 Module to decode Ethernet Packets
170 "Net::RawIP"
172 Module to send encoded data out.
173 "Net::PcapUtils"
175 Utility module to be used for packet capture.
176
178 Copyright (c) 2002 Chander Ganesan.
179 This package is free software and is provided "as is" without express
181 or implied warranty. It may be used, redistributed and/or modified
182 under the terms of the Perl Artistic License (see
183 http://www.perl.com/perl/misc/Artistic.html)
184 This software and all associated data and documentation ('Software') is
186 available free of charge. You may make copies of the Software but you
187 must include all of this notice on any copy.
188 The Software was developed for research purposes does not warrant that
190 it is error free or fit for any purpose. The author disclaims any
191 liability for all claims, expenses, losses, damages and costs any user
192 may incur as a result of using, copying or modifying the Software.
193
195 Chander Ganesan <cganesan@cpan.org<gt>
196perl v5.32.1 2021-01-27 SpanningTree(3)