Trunking issues when changing VTP to transparent

Answered Question
Aug 28th, 2009
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Thanks in advance to anyone who can help. I have a bunch of 3548XL (I know they are old and EOL) so I'm in the process of changing their VTP mode from client to transparent, the VTP server is our core 6500 router and all 3548XL closet switches are VTP clients, Vlans are manually prunned at both ends of the trunks...I have issues with 2 out of the 14 3548XL switches that I performed the VTP mode change on, there is no difference between them -same code, same hardware, same configuration but every time I change the VTP mode to transparent users begin experiencing intermittent network access, I loose connectivity to the switch via telnet, there is connectivity for a few seconds then connectivity is lost...has anyone experienced something similar?

Correct Answer by jbrenesj about 7 years 8 months ago

Is VTP pruning disabled on the 6500?

It's a fact that pruning has issues when there are transparent switches meaning that the VLANs can get prunned the wrong way. What do you mean with "Vlans are manually prunned at both ends of the trunks", is this using switchport trunk allowed vlan X or switchport trunk pruning vlan X ?

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Correct Answer
jbrenesj Fri, 08/28/2009 - 11:44
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Is VTP pruning disabled on the 6500?

It's a fact that pruning has issues when there are transparent switches meaning that the VLANs can get prunned the wrong way. What do you mean with "Vlans are manually prunned at both ends of the trunks", is this using switchport trunk allowed vlan X or switchport trunk pruning vlan X ?

Borman Bravo Fri, 08/28/2009 - 12:05
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I use "switchport trunk allowed vlan X" on the core and access switch trunk interfaces...

BTW This imy VTP server VTP config:



VTP Version : 2

Configuration Revision : 135

Maximum VLANs supported locally : 1005

Number of existing VLANs : 94

VTP Operating Mode : Server

VTP Domain Name : OV

VTP Pruning Mode : Enabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0xE9 0x2B 0x94 0x73 0x12 0x1E 0x65 0xDF

Configuration last modified by 10.10.1.2 at 8-11-09 14:40:49

jbrenesj Fri, 08/28/2009 - 12:14
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I suggest disabling vtp pruning on the vtp server.


What you can do is check the show interfaces trunk and see if the trunk port going to one of the affected switches has all of the necesary vlans in the "spanning-tree forwarding state and not pruned" section of the output

Borman Bravo Fri, 08/28/2009 - 12:24
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So "no vtp pruning" on the VTP server? is this a safe operation?

jbrenesj Fri, 08/28/2009 - 12:34
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Yes, it's safe but as always, better to apply any changes after working hours.

The only effect is that now all the vlans will be forwarding in all trunks but since you have manually allowed only the required vlans then no extra broadcast/flooding will be sent over all the trunks

Borman Bravo Fri, 08/28/2009 - 12:53
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This actually fixed my problem, thank you very much for your help.

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