Chapter 1 Mstp Region-Configuration; Mstp Overview; Mstp Concepts - Huawei Quidway S3500 Series Operation Manual

Operation Manual - STP
Quidway S3500 Series Ethernet Switches

Chapter 1 MSTP Region-configuration

1.1 MSTP Overview

MSTP stands for Multiple Spanning Tree Protocol, which is compatible with STP and
RSTP.
STP cannot transit fast. Even on the point-to-point link or the edge port, it has to take an
interval as long as twice forward delay before the network converges.
RSTP can converge fast, but still has the drawback, that is, all the network bridges in a
VLAN share a spanning tree and the redundant links cannot be blocked by VLAN.
MSTP makes up for the drawback of STP and RSTP. It makes the network converge
fast and the traffic of different VLAN distributed along their respective paths, which
provides a better load-balance mechanism for the redundant links.
MSTP associates VLAN and the spanning tree and divides a switching network into
several regions, each of which has a spanning tree independent of one another. MSTP
prunes the network into a loopfree tree to avoid proliferation, it also provides multiple
redundant paths for data forwarding to implement the VLAN data forwarding
load-balance.

1.1.1 MSTP Concepts

There are 4 MST region in Figure 1-1. The concept of MSTP will be introduced with this
figure in the followed text.
CIST: Common and Internal
MSTI: Multiple Spanning
Region A0
vlan 1 mapping to Instance 1, region root B
vlan 3 mapped to Instance 2
Other vlans mapped to CIST
Figure 1-1 Basic MSTP concepts
Spanning Tree
Tree Instance
BPDU
A
CST: Common
Spanning Tree
B
C
D
, region root C
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Chapter 1 MSTP Region-configuration
Region A0
vlan 1 mapped to Instance 1
vlan 2 mapped to Instance 2
Other vlans mapped to CIST
BPDU
BPDU
Region B0
vlan 1 mapped to Instance 1
vlan 2 mapped to Instance 2
Other vlans mapped to CIST
Region C0
vlan 1 mapped to Instance 1
vlan 2 and 3 mapped to Instance 2
Other vlans mapped to CIST
1-1