Purpose
After a spanning tree protocol is configured on an Ethernet switching network, the protocol
calculates the network topology to implement the following functions:
l
Loop prevention: The spanning tree protocol blocks redundant links to prevent potential
loops on the network.
l
Link redundancy: When an active path fails, a redundant link is activated to ensure network
connectivity.
6.2 Principles
This section describes how STP/RSTP works.
6.2.1 Background
STP prevents loops on a local area network (LAN). The switching devices running STP exchange
information with one another to discover loops on the network, and block certain ports to
eliminate loops. With the growth in scale of LANs, STP has become an important protocol for
a LAN.
Figure 6-1
Typical LAN networking
1
2
3
4
5
Host A
Host B
S1
S2
port1
port2
port1
port2
Data flow
On the network shown in
, the following situations may occur:
l
Broadcast storms cause a breakdown of the network.
If a loop exists on the network, broadcast storms may occur, leading to a breakdown of the
network. In
, STP is not enabled on the switching devices. If Host A sends a
broadcast request, both S1 and S2 receive the request on port 1 and forward the request
through their port 2. Then, S1 and S2 receive the request forwarded by each other on port
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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