DEC and 802.1d BPDU Formats

Available Languages

Updated:May 2, 2005

Document ID:10691

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Introduction

Before You Begin

Conventions

Prerequisites

Components Used

Bpdu Formats

Related Information

DEC code:     E1
bpdu type:    19 hello, 02 topology change notice
version:      01
bit field:    1 byte
  1 : topology change notice
  2 : topology change notice ack
  3 : unused    0
  4 : unused    0
  5 : unused    0
  6 : unused    0
  7 : unused    0
  8 : use short timers
root priority:   2 bytes
root id:         6 bytes
root path cost:  2 bytes
bridge priority: 2 bytes
bridge id:       6 bytes
port id:         1 byte
message age:     1 byte
hello time:      1 byte
max age:         1 byte
forward delay:   1 byte

An IEEE 802.1d Bpdu has the following format:

protocol id:   0000 IEEE 802.1d
version id:    00
bpdu type:     00 config bpdu, 80 tcn bpdu
bit field:     1 byte
  1 : topology change flag
  2 : unused    0
  3 : unused    0
  4 : unused    0
  5 : unused    0
  6 : unused    0
  7 : unused    0
  8 : topology change ack
root priority    2 bytes
root id:         6 bytes
root path cost:  4 bytes
bridge priority: 2 bytes
bridge id:       6 bytes
port id:         2 bytes
message age:     2 bytes in 1/256 secs
max age:         2 bytes in 1/256 secs
hello time:      2 bytes in 1/256 secs
forward delay:   2 bytes in 1/256 secs