Question on 'strange' STP behavior

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Dec 14th, 2009
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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.

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sridsdale Mon, 12/14/2009 - 14:27
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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?

news2010a Mon, 12/14/2009 - 14:51
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Yes, I adjusted trunks on both ends accordingly to vlan 7.

Giuseppe Larosa Tue, 12/15/2009 - 00:28
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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


news2010a Tue, 12/15/2009 - 12:32
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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).



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