Table 6-7
Fields in a BPDU
Field
Byte
s
Description
Protocol Identifier
2
The value is fixed at 0.
Protocol Version
Identifier
1
The value is fixed at 0.
BPDU Type
1
Indicates the type of a BPDU. The value is one of the
following:
l
0x00: configuration BPDU
l
0x80: TCN BPDU
Flags
1
Indicates whether the network topology has changed.
l
The rightmost bit is the Topology Change (TC) flag.
l
The leftmost bit is the Topology Change Acknowledgment
(TCA) flag.
Root Identifier
8
Indicates the BID of the current root bridge.
Root Path Cost
4
Indicates the accumulated path cost from a port to the root
bridge.
Bridge Identifier
8
Indicates the BID of the bridge that sends the BPDU.
Port Identifier
2
Indicates the ID of the port that sends the BPDU.
Message Age
2
Records the time that has elapsed since the original BPDU
was generated on the root bridge.
If the configuration BPDU is sent from the root bridge, the
value of Message Age is 0. Otherwise, the value of Message
Age is the total time spent to transmit the BPDU from the root
bridge to the local bridge, including the transmission delay.
In real world situations, the Message Age value of a
configuration BPDU increases by 1 each time the
configuration BPDU passes through a bridge.
Max Age
2
Indicates the aging time of a BPDU.
Hello Time
2
Indicates the interval at which BPDUs are sent.
Forward Delay
2
Indicates the period during which a port stays in the Listening
and Learning states.
shows the Flags field. Only the leftmost and rightmost bits are used in STP.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
6 STP/RSTP Configuration
Issue 01 (2014-11-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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