Port
State
Description
Discardin
g
A port in the Discarding state can only receive BPDUs.
The following parameters affect the STP port states and convergence.
l
Hello Time
The Hello Time specifies the interval at which an STP device sends configuration BPDUs
and Hello packets to detect link failures.
When the Hello Time is changed, the new value takes effect only after a new root bridge
is elected. The new root bridge adds the new Hello Time value in BPDUs it sends to non-
root bridges. The Hello Time does not control transmission of TCN BPDUs when the
network topology changes.
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Forward Delay
The Forward Delay timer specifies the length of the delay before a port state transition.
When a link fails, STP calculation is triggered and the spanning tree structure changes.
However, new configuration BPDUs cannot be immediately transmitted over the entire
network. If the new root port and designated port forward data immediately, transient loops
may occur. Therefore, STP defines a port state transition delay mechanism. The newly
selected root port and designated port transition to the Forwarding state after two Forward
Delay intervals. In this manner, the new BPDUs can be transmitted over the network before
the new root port and designated port start to forward data, preventing transient loops.
NOTE
The Forward Delay timer specifies the duration in which a port stays in Listening and Learning states.
The default value is 15 seconds. This means that the port stays in the Listening state for 15 seconds
and then stays in the Learning state for another 15 seconds. The port is blocked when it is in the
Listening or Learning state, which is key to preventing transient loops.
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Max Age
The Max Age specifies the aging time of BPDUs. This parameter can be manually
configured on the root bridge.
The Max Age is spread to the entire network with configuration BPDUs. After a non-root
bridge receives a configuration BPDU, it compares the Message Age value with the Max
Age value in the received configuration BPDU.
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If the Message Age value is smaller than or equal to the Max Age value, the non-root
bridge forwards the configuration BPDU.
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If the Message Age value is larger than the Max Age value, the configuration BPDU is
aged and forwarded by the non-root bridge. When this happens, the network size is
considered too large and the non-root bridge disconnects from the root bridge.
NOTE
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.
provides the timer values defined in IEEE 802.1D.
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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