Chapter 13 Spanning Tree Protocol
GS2210 Series User’s Guide
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VLAN- t o- MST I nst ance m apping
13.10.3 MST Instance
An MST I nst ance ( MSTI ) is a spanning t r ee inst ance. VLANs can be configur ed t o r un on a specific
MSTI . Each cr eat ed MSTI is ident ified by a unique num ber ( known as an MST I D) know n int er nally
t o a r egion. Thus an MSTI does not span acr oss MST r egions.
The follow ing figur e show s an exam ple w her e t here ar e t w o MST r egions. Regions 1 and 2 have 2
spanning t r ee inst ances.
Figure 104
MSTI s in Differ ent Regions
13.10.4 Common and Internal Spanning Tree (CIST)
A CI ST r epr esent s t he connect ivit y of t he ent ir e net w or k and it is equivalent t o a spanning t r ee in
an STP/ RSTP. The CI ST is t he default MST inst ance ( MSTI D 0) . Any VLANs t hat are not m em ber s of
an MST inst ance ar e m em ber s of t he CI ST. I n an MSTP- enabled net w or k, t her e is only one CI ST
t hat r uns bet w een MST r egions and single spanning t r ee devices. A net wor k m ay cont ain m ult iple
MST r egions and ot her net w or k segm ent s r unning RSTP.
Figure 105
MSTP and Legacy RSTP Net w ork Exam ple
