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Spanning Tree topology change

Hi all,


My network environment is traditional 3 layers network, which is composed of Core, Aggregation and Edge.

Core router is the place where we set gateway, and I also set Core's spanning tree priority with 8192 to make Core play as a root.


Here is the situation, there was vlan 100 on Core and Aggregation but not on Edge. I was trying to create vlan 100 on Edge. Edge's spanning tree priority was default(32768), so I was sure Edge will not take the root. After I created vlan 100 on Edge, I saw some log like "Topology change.......@#$@#%" showed on Edge. 


I looked up some description of topology change as below

Principle of Operation

This section explains how a bridge advertises a topology change at the Bridge Protocol Data Unit (BPDU) level.

It has already been briefly explained when a bridge considers it detected a topology change. The exact definition is:

  • When a port that was forwarding is going down (blocking for instance).

  • When a port transitions to forwarding and the bridge has a designated port. (This means that the bridge is not standalone.)

The process to send a notification to all bridges in the network involves two steps:

  • The bridge notifies the root bridge of the spanning tree.

  • The root bridge "broadcasts" the information into the whole network.


Here are my questions...

1.) When I saw "topology change....." log on Edge, does this mean Edge receives the topology change BPDU from root?

2.) The one who initializes the TCN should be Aggregation, do I think right? Because Aggregation got a port transitions to forwarding and it also has  designated port, whereas Edge only has root port.

3.) In this case, even Edge's priority is too big to take the root, does Aggregation still sends the TCN to root(Core)?

4.) Followed by Q3, when root(Core) receives the TCN, does root also broadcast the information to all members even Edge is not able to be root?

5.) Followed by Q4, in this case, do all other members still flush their MAC table when receive the broadcast from root?