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Problem with pruning between VTP server and VTP transparent

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Feb 7th, 2006
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We are installing a new switch in our infrastructure. This is a switch that cannot be joined in our VTP domain because the VLAN's we create on this switch may not be visible on other switches.


So our VTP server is a Cat 6500 running CatOS ver6.3. The new switch in transparent mode runs IOS 12.2SX.


Both switches are connected via ISL trunks.


VTP pruning is enabled on the VTP server.


Now the problem is that VLAN10 (that is configured on the VTP server, and manually on the transparent) is pruning on the trunk between those 2 switches. Because of this no broadcasts are received on the new switch, and this is our problem


We found out that you can enable per interface and per vlan pruning on the IOS switch, but as fare as we could find, this was not possible on the Cat OS.


Anyone an idea how we can solve this problem without having the new server to be a VTP client?


An other idea could be to disable VTP pruning on VLAN 10 on the VTP server, but due to to impact on a production network, I prefer an other solution.


Many thanks.


Koen



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nethelper Tue, 02/07/2006 - 06:01
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Hello Koen,


what are you trying to accomplish ? If the switch is configured in VTP transparent mode, it effectively becomes a standalone switch, and does not exchange any VLAN information with any other switch (except for relaying VTP advertisments out the trunk ports, if your run VTP version 2).

Why would you want broadcasts to be exchanged between both switches, while keeping the VLAN information invisible to the rest of the network ? Or do you want just certain VLANs to be invisible ?

Sorry if I misunderstood your setup, but maybe you can clarify...


Regards,


Nethelper

glen.grant Tue, 02/07/2006 - 08:38
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You can definetly prune on a catos box , all you need to do is use the "clear trunk " command to include the vlan you want to prune .

Francois Tallet Tue, 02/07/2006 - 10:51
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Hi Koen,

I used to be familiar with VTP's state machines but it's been a while... CatOS and IOS are behaving sligthly differently on the top of that:-(

I could remember that VTP pruning was able to determine when the trunk was coming up whether the remote neighbor was able to run pruning or not. If so, then it would expect some joins for the required vlans. It looks like in your case, the switch running VTP pruning is expecting some joins from its transparent neighbor (weird).

Could it be that you have another switch running VTP behind the transparent switch? Could you try to configure your transparent switch as a server but in a different domain? That should achieve roughly the same functionality and you can explicitly disable pruning. After the change, make sure to bring the trunk down and up again.

Sorry for the approx answer, a real VTP expert should be able to answer exactly your question with the details you gave.

Regards,

Francois

SDWorx_2 Thu, 02/16/2006 - 07:26
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Hi all,


Many thanks for the responses and my apologies for responding so late. but due to a lot of work I was not able to update this post.


There is one VTP server in our network, all other switches are clients. Now the reason that we configured the new server as transparent is due to security reasons. All VLAN's added on the new switch may not be visible on the other switches in the network. But 2 VLAN's configured on the "old" switch should be know on the new switch.. I know this seams complex, but is in this way the setup is most secure for us.


Now we have found a (temporary?) solution, and this is that we disabled pruning for that particular VLAN. This causes many more broadcast on the network, but the VLAN is now accessible from the new switch.


We've been told that VTP pruning is not that popular. The gain is not really spectacular. Anyone that shares this thinking?


Thanks again.


Koen


Hi Koen,


I think you may be getting confused between VTP pruning and manually pruning VLANs from trunk links. VTP pruning is not that popular because best-practices dictate that if a VLAN is not used on an edge switch, the VLAN should be manually pruned from the trunk link in order to avoid spanning-tree problems. VTP pruning does NOT prevent spanning-tree from functioning on certain VLANs on a switch.


It's hard for me to tell exactly what you are doing from the e-mail thread, but if I am reading this correctly, you have 2 VLANs (say 10,11) that need to be configured on the transparent switch so that communication can be maintained to the rest of the network. If you are creating new separate VLANs (say 12,13), these would be created manually on the transparent switch, along with the existing two VLANs.


One thing that is confusing me a bit is how are you handling Layer 3 for the new VLANs without propagating them to an upstream 6500/MSFC? Is the transparent switch also L3?

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