VTP pruning with transparent switch in the middle

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May 6th, 2008
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hi

I have three switches A-B-C. A is the server and B & C are clients. They are connected via trunk links. All switches are running VTP version 2. I converted Switch B to transparent and changed the vtp domain name to be different from the other two.

Issue # 1 According to Cisco doc I should be able to add a vlan on switch A and it propagate to Switch C thru the transparent Switch B in version 2. It's not happening until i make the vtp domain name on switch B the same?



Issue #2 - Back to the scenario where A-B-C are in the same vtp domain and switch A is the server and B and C are clients. I have devices off Vlan 15 off Switch A and C. I enabled pruning and see the expected results which are since traffic is requested by C it is not pruned on the trunk link from towards C. Now i change the middle switch B to transparent. I expect to lose reachability from the device connected to VLAN 15 on Switch A to the device connected to VLAN 15 on C as the middle switch is transparent. however i still have connectivity. Accoring to Cisco DOC i am to remove VLAN 15 from the prune list on the link connected to B for reachability. But it works even without me doing this step. The switches are 3560's.

Sorry for the long post but i have spent a lot of time trying to figure this out


http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_40_se/configuration/guide/swvtp.html#wp1072526

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bvsnarayana03 Wed, 05/07/2008 - 02:26
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Issue#1: Transparent switches forward the vtp advertisements irrespective of the domain they are in.


Issue#2: This proves the above concept.

dathaide Wed, 05/07/2008 - 05:37
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Thanks for replying


Have to disagree with your conclusion to Issue #1. I have it lab'd up of different sets of equipment and arrived a the same conclusion that VTP advertisements will not propagate if domain names are different even in version 2.


Issue #2 - Then why does Cisco suggest when one configures vtp pruning with a transparent switch in the picture the upstream switch needs to manaully NOT prune the vlans thru the transparent switch. It works without even doing that.

Thanks

bvsnarayana03 Wed, 05/07/2008 - 10:58
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Hi Dwayne,

My understanding of vtp was the same as your's until i came across a discussion on this forum sometime ago.


You may want to check the vtp version on transparent switch, is it v2 as well?


Refer this link:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network Infrastructure&topic=LAN, Switching and Routing&CommCmd=MB?cmd=display_location&location=.2cbe7b75

bvsnarayana03 Wed, 05/07/2008 - 02:26
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Issue#1: Transparent switches forward the vtp advertisements irrespective of the domain they are in.


Issue#2: This proves the above concept.

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