Traffic through VTP transparent switches

tandlauer · ‎06-18-2009

---------- ---------- ----------

| SW 1 |---trunk---| SW 2 |---trunk---| SW 3 |--------- rest of VTP domain

---------- ---------- ----------

| |

client 1 client 2

(I hope the little schema is readable, because in the post form it wasn't. If not I'm gonna send another one in jpg)

Hi, this is a question about a strange observation. Has someone already see this, or is it something normal and explanable ?

The situation is : all 3 swithes are in the same VTP domain (dom1), in client mode, in version 1, without password.

Everything's OK. The goal is to move SW1 and SW 2 in transparent mode in order to create a local VLAN that is useless in the

rest of the VTP domain.

The problem is : when I configure SW 1 in transparent mode, SW 1 becomes isolated, he's not able to join the rest of the

network, and the client 1 neither. In this state, everything is ok on SW 2. When then I configure SW 2 in transparent mode

too, SW 1 retreive its connectivity and client 1 too, and the situation is globally OK.

The question is : why is there a connectivity problem when only SW 1 is in transparent mode ??? I may have understood if the

domain were not the same, but it is not the case.

I hope this question is not so stupid.

Regards

Thomas

tandlauer · ‎06-18-2009

here is the schema in jpg

Mohamad Qayoom · ‎06-18-2009

Can you send "sh vtp status" from both switches?

Thanks,

Mohamad

tandlauer · ‎06-19-2009

show vtp status for SW1 before modification

WS-2950-LVD-3#sh vtp status

VTP Version : 2

Configuration Revision : 73

Maximum VLANs supported locally : 250

Number of existing VLANs : 43

VTP Operating Mode : Client

VTP Domain Name : dom1

VTP Pruning Mode : Enabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0xB8 0x3C 0x72 0x69 0xAC 0x11 0x61 0x37

Configuration last modified by xxx

For SW2 :

WS-3560-LVD-2#sh vtp status

VTP Version : running VTP1 (VTP2 capable)

Configuration Revision : 73

Maximum VLANs supported locally : 1005

Number of existing VLANs : 43

VTP Operating Mode : Client

VTP Domain Name : dom1

VTP Pruning Mode : Enabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0xB8 0x3C 0x72 0x69 0xAC 0x11 0x61 0x37

Configuration last modified by xxx

For SW3 :

SW-C2960-30T1-020#sh vtp status

VTP Version : 2

Configuration Revision : 73

Maximum VLANs supported locally : 255

Number of existing VLANs : 43

VTP Operating Mode : Client

VTP Domain Name : dom1

VTP Pruning Mode : Enabled

VTP V2 Mode : Disabled

VTP Traps Generation : Enabled

MD5 digest : 0xCF 0xBC 0xD1 0x09 0xDB 0x14 0x3C 0xE3

Configuration last modified by xxx

davy.timmermans · ‎06-18-2009

what do you mean with:

cannot join the rest of the network?

connectivity issues?

If yes, make sure that the VLANS you create on sw1, are known on the other switches and allowed over the trunk

tandlauer · ‎06-19-2009

Thank you for your answer.

Yes, when i said "cannot join te rest of the network" I meant "connectity issue".

Of course the vlans known on the 3 switches are the same, because they were all in client mode before the modification, and were synchronized. When you switch in transparent mode, the vlan database in not reseted, just the revision number.

The vlan for which there is connectivity issue are allowed on the trunks.

i.va · ‎06-19-2009

Hi,

I see you have pruning enabled. This might be an issue when changing to transparent mode. Take a look at the following thread:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=LAN%2C%20Switching%20and%20Routing&topicID=.ee71a04&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40^1%40%40.2cd35857/3#selected_message

Thotsaphon Lueangwattanaphong · ‎06-19-2009

Thomas,

Please post a "show interface trunk" command on Sw1 and Sw2.

Toshi

tandlauer · ‎06-19-2009

Thank you for the answer.

I had already thought about this, it is a good idea, but I would have understood if I moved first the SW 2 int transparent which would have cut the domain between SW1 and SW3 (although the domain is the same on all switches and so vtp v1 should let the vtp packets pass). But I first moved SW1. Besides, the issue should be the same on SW2 in this case, but it is not.

I took a look at the command "show int trunk" but the Vlan for which there is the issue is not pruned, wherever ! That's why I don't understand.

Paul Malysz · ‎06-22-2009

Everything you wanted to know about VTP:

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094c52.shtml

There is a flash animation that goes along with the above doc, which is here: http://www.cisco.com/warp/public/473/vtp_flash/

I didn't see a VTP server on your three switches.

tandlauer · ‎06-23-2009

In fact I think the thread you indicated is very interesting !

Thanks to paul malysz too, I took a look to the troubleshooting part of the VTP guide and I conclude that VTP pruning and mode transparent are not good friends at all... even if the domain is correct.

Regards

Thomas