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Community Member

4507 Topology Change Problem

We have some 500 switches connected to cisco 4507 as L2 Tier-1 Aggregator. I am frequently facing problem of Topology change Notifications.

The Entire network is geographically separated point to point star network without any redundant paths. After enabling Edge port on all the 500 switches the topology change is very much in control but still it is there.

Is there any method that we can divide this network without putting any L3 device so that topology change will be limited to that particular small part of network

MST is running on Cisco 4507 and remaining RSTP on remaining all switches


Re: 4507 Topology Change Problem

On your access switches make sure you have spanning tree portfast turned on for all user ports otherwise everytime a user comes on the air you will see a TCN . If your connecting links are stable you should see very few TCN"s.TCN's are not a bad thing as long as you are not getting a ton of them , if so you have a problem somewhere .

Good link .

Community Member

Re: 4507 Topology Change Problem


I totally agree on what u r saying.. and i know that TCN is important...

What i am looking for is some solution where i can divide this into 5-10 parts so as if one part is affected others should not.

Can i get this kind of division by implementing 5-10 different MST instances on 4507...Because as per my understanding the MST instances are configured vlan wise..Is there any method to configure per port wise....where i can map as set of ports say 5/1 to 5/24 in one MST instance and 5/25 to 5/48 in another MST instance.

Community Member

Re: 4507 Topology Change Problem

Generally it is stable only...But the problem comes when link towards one or two sites fluctuates. As i told all the other sites are connected to geographically different locations thorugh Ethernet over SDH/SONET

So during during those problematic hours TCN reaches nearly one minute and CPU utilization also goes high as It has to rebuild a mac table of 25K

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