Document ID: 10691
Updated: May 02, 2005
Contents
Introduction
This document describes DEC and IEEE 802.1d Bridge Protocol Data Unit (Bpdu) formats.
Before You Begin
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.
Prerequisites
There are no specific prerequisites for this document.
Components Used
This document is not restricted to specific software and hardware versions.
Bpdu Formats
A DEC Bpdu has the following format:
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
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.
Updated: May 02, 2005
Document ID: 10691