Refer to the Exhibit.
Sw-1 and Sw-2 as shown in the exhibit are configured as follows:
Sw-1
admin@Sw-1# show
configuration-name juniper;
revision-level 1;
bridge-priority 4k;
msti 1 {
vlan 10;
}
msti 2 {
vlan 20;
}
Sw-2
configuration-name juniper;
revision-level 1;
bridge-priority 8k;
msti 1 {
vlan [ 10 15 ];
}
msti 2 {
vlan 20;
}
Which bridge is the root for CIST?
A.
Neither is root for CIST.
B.
Both are root for CIST.
C.
Sw-1 is the only root bridge for CIST.
D.
Sw-2 is the only root bridge for CIST.
Explanation:
C?
I believe that there is only one CIST and because of SW1 bridge-priority 4k.
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Please try to add intelligent and useful comments. You can use Google to research if you do not understand anything about VSTP. Anyone can post what they believe, but it is better if you post what you know and even better still if you provide some supporting documents, links or explanation.
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due to vlan mismatch config, they are not on the same MSTP instance that why there are both root.
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There will be two diffrent MST regions, one CST to interconnect them and one CIST root bridge.
The common and internal spanning tree (CIST) is a single topology that connects all switches (RSTP and MSTP devices) through an active topology. The CIST includes a single spanning tree as calculated by RSTP together with the logical continuation of connectivity through MST regions. MSTP calculates the CIST and the CIST ensures connectivity between LANs and devices within a bridged network.
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If MSTI instances doesn’t match it will be one CIST root but 2 diffrent CIST regional roots (because of 2 diffrent regions). IF MSTI instances match it will be one CIST root and one CIST regional root (one region). 100% correct answer
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