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New Member

Question on 'strange' STP behavior

Hi, can you help answer this question. This is a continuation from another thread. Please see attached diagram for details.

Imagine I attempt to change 2950C from vlan 22 to vlan 7. I created the vlan 7 database on 2950C, then the SVI int vlan 7 and assigned correct IP. I configured the default-gateway to vlan 7 and assigned 'int range f0/1 - 22' to access vlan 7 - OK. Then I deleted all vlan 22 information from 2950C. From the network I was able to ping SVI vlan 7 OK.

Twenty minutes later people complained that servers pointing to other switches on vlan 7 stopped responding.


Based on the mac address for 2950A and 2950C, I believe that 2950A should remain as the root bridge for vlan 7. Even though the ip default-gateway is not set on 2950A, in theory I think this is not enough to explain why when I made changes on 2950C to vlan 7 servers on vlan 7 stopped working. 

Note: I am aware the 4507 should be setup as the STP root.This network as is now is suboptimal. At this point I just want to make sure I can justify why trying to make 2950C as a vlan 7 configuration did not work.

New Member

Re: Question on 'strange' STP behavior

Looking at the Visio the trunks from the 2950C to the 4507s was only allowing VLAN 22. You don't mention changing this when you added VLAN 7 to the switch. Did you allow VLAN 7 on the trunk at both ends?

New Member

Re: Question on 'strange' STP behavior

Yes, I adjusted trunks on both ends accordingly to vlan 7.

Hall of Fame Super Silver

Re: Question on 'strange' STP behavior

Hello Marlon,

I think it would have been better to go on using the previous thread.

you can use the next link  on bottom right to go to older threads ( next = older it may look like strange I know)

Best Regards


New Member

Re: Question on 'strange' STP behavior

Sorry Giuslar. In fact I attempted to search the other thread, but I didn't find it (in the past I used to find my posts easily by doing a search. On this new imrproved website that search feature returns different results. I will play a little more today).