Cisco Catalyst 2975 Software Configuration Manual page 452

Understanding MSTP
The IST connects all the MSTP switches in the region and appears as a subtree in the CIST that
encompasses the entire switched domain. The root of the subtree is the CIST regional root. The MST
region appears as a virtual switch to adjacent STP switches and MST regions.
Figure 17-1
regional root for region 1 (A) is also the CIST root. The CIST regional root for region 2 (B) and the CIST
regional root for region 3 (C) are the roots for their respective subtrees within the CIST. The RSTP runs
in all regions.
Figure 17-1 MST Regions, CIST Masters, and CST Root
D
Legacy IEEE 802.1D
B
IST master
MST Region 2
Catalyst 2975 Switch Software Configuration Guide
17-4
shows a network with three MST regions and a legacy IEEE 802.1D switch (D). The CIST
IST master
A
and CST root
MST Region 1
Chapter 17
C
IST master
MST Region 3
Configuring MSTP
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