Protection
Function
Scenario
Configuration Impact
Root
protection
Due to incorrect
configurations or malicious
attacks on the network, a
root bridge may receive
BPDUs with a higher
priority than its own priority.
Consequently, the legitimate
root bridge is no longer able
to serve as the root bridge
and the network topology is
changed, triggering
spanning tree recalculation.
This may transfer traffic
from high-speed links to
low-speed links, causing
traffic congestion.
If a designated port is enabled with the root
protection function, the role of the port cannot
be changed. Once a designated port that is
enabled with root protection receives RST
BPDUs with a higher priority, the port enters
the Discarding state and does not forward
packets. If the port does not receive any RST
BPDUs with a higher priority before a period
(generally two Forward Delay periods)
expires, the port automatically enters the
Forwarding state.
Loop
protection
A root port or an alternate
port will age if link
congestion or a one-way link
failure occurs. After the root
port ages, a switching device
may re-select a root port
incorrectly. After the
alternate port ages, the port
enters the Forwarding state.
Loops may occur in such a
situation.
After loop protection is configured, if the root
port or alternate port does not receive RST
BPDUs from the upstream switching device
for a long time, the switching device notifies
the NMS that the port enters the Discarding
state. The blocked port remains in the
Blocked state and no longer forwards packets.
This function helps prevent loops on the
network. The root port transitions to the
Forwarding state after receiving new BPDUs.
Pre-configuration Tasks
Before configuring basic RSTP functions, complete the following task:
l
Configuring basic RSTP functions
NOTE
Configure an edge port on the switching device before configuring BPDU protection.
Data Preparation
To configure basic RSTP functions, you need the following data.
No.
Data
1
Number of the port on which root protection is to be enabled
2
Number of the port on which loop protection is to be enabled
Huawei AR3200 Series Enterprise Routers
Configuration Guide - LAN
7 STP/RSTP Configuration
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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