Here I come with my first quiz about a (rather common) MSTP misconfiguration that does not look very obvious on the first encounter.
This is my first quiz and I chose an MSTP misconfiguration scenario that could be easily overlooked on the first encounter.
You have a typical network with 2 COREs and 2 DIST switches running Multiple Spanning Tree Protocol. The server team requested that servers in vlans 100 to 199 will be considered privileged. You implemented MSTP in the following way:
- created a dedicated instance in MSTP (vlans 100-199 mapped to MST 1) and made CORE-2 as ROOT
- left all other vlans in MST 0 with CORE-1 as ROOT
- first trunk between CORES (core-1:Gi0/13 <> core-2:Gi0/13) was dedicated only to vlans 100-199 (
switchport trunk allowed vlan 100-199)
- second trunk between CORES (core-1:Gi0/14 <> core-2:Gi0/14) allows all vlans
After your implementation, server team confirmed that all communications are ok (in both privileged vlans 100-199 and also in all other existing vlans).
All good, everybody's happy ... until a cable got disconnected on DIST-2: the fiber between
DIST-2:Gi0/13 and CORE-1:Gi0/19.
No problem, you say, DIST-2 still has one uplink to CORE-2 ... but very soon you receive
What do you think the problem is? What would be the best commands to troubleshoot this issue and on what device(s)?
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