3Com 10014298 manual MST Region, Vlan Mapping Table, Internal Spanning Tree IST

Figure 53 MSTP Concepts

Region A0

vlan 1 mapped to Instance 1 vlan 2 mapped to Instance 2 Other vlans mapped to CIST

CIST: Common and Internal Spanning Tree

MSTI: Multiple SpanningTree Instance

Region A0		BPDU		BPDU
vlan 1 mapped to Instance 1,		A		CST: Common
region root B
	B		C
vlan 2 and 3 mapped to				Spanning Tree
Instance 2, region root C		D
Other vlans mapped to CIST

BPDU

Region C0

vlan 1 mapped to Instance 1

vlan 2 and 3 mapped to Instance 2 Other vlans mapped to CIST

MST Region

MSTP Overview 187

Region B0

vlan 1 mapped to Instance 1 vlan 2 mapped to Instance 2 Other vlans mapped to CIST

A multiple spanning tree region contains several physically and directly connected MSTP-capable switches sharing the same region name, VLAN-spanning tree mapping configuration and MSTP revision level configuration, and the network segments between them. There can be several MST regions on a switching network. You can group several switches into a MST region, using MSTP configuration commands. For example, in Figure 53, in MST region A0, the 4 switches are configured with the same region name, vlan mapping table (VLAN1 map to instance 1, VLAN 2 map to instance 2, other VLAN map to instance 0), and revision level (not indicated in Figure 53).

VLAN Mapping Table

A VLAN mapping table is an attribute of an MST region and is used for describing the mapping relationship of VLAN and STI. For example, the VLAN mapping table of MST region A0 in Figure 53 is VLAN1 map to instance 1, VLAN 2 map to instance 2, other VLAN map to instance 0.

Internal Spanning Tree (IST)

The entire switching network has a Common and Internal Spanning Tree (CIST). An MSTP region has an Internal Spanning Tree (IST), which is a fragment of CIST. For example, every MST region in Figure 53 has an IST.

Common Spanning Tree (CST)

CST connects the spanning trees of the MST region. Taking every MST region as a “switch”, the CST can be regarded as their spanning tree generated with STP/RSTP. For example, the red line indicates the CST in Figure 53.

Common and Internal Spanning Tree (CIST)

A single spanning tree made of IST and CST. The CIST in Figure 53 is composed of each IST in every MST region and the CST.