12-09-2008 12:49 PM - edited 03-06-2019 02:53 AM
We are running transparent mode for all the switches in our network. However, we experienced port channcel failed after we changed the VTP domain name on the switch sitting on one end of the port channel.
I am wondering if any one else experienced the same thing and any expert could explain why?
Thanks,
Cedar
12-09-2008 12:57 PM
At first glance I see no relationship between the VTP domain and the portchannel.
Sure you didn't config something else? It would be a good idea to paste the Portchannel config and the individual ports. and maybe also an show ether summ
is the Portchannel down/down?
12-09-2008 01:34 PM
Hello Cedar,
the VTP domain information is carried within DTP frames so if your etherchannel bundles are negotiating their trunk status the trunk can be disabled if the two endpoints detect a VTP domain mismatch.
This is thought as a sort of security feature: if there is a change of VTP domain the two devices can be managed by different groups so you need to configure the trunks manually while before they could be negotiated
Hope to help
Giuseppe
12-09-2008 01:54 PM
Hi Giuseppe,
You mean VTP domain mismatch happens even on the switches in transparent mode?
Thanks,
Cedar
12-09-2008 02:06 PM
Hello Cedar,
if the trunk status is negotiated DTP protocol carries this information the VTP domain name and the two parts can compare it and decide to not form a trunk if it is different.
I think this can happen even if the switch is in VTP transparent mode because it is another protocol DTP that makes these negotiations and probably the VTP mode of the switch is not taken in account.
see
http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080890613.shtml#topic5
Section Data Traffic Blocked between VTP Domains
Hope to help
Giuseppe
12-09-2008 02:22 PM
That is correct if it is a negotiated trunk connection and the vtp domain names do not match it will not stay active even in transparent mode . In this case you are forced to go to "switchport mode trunk" in the configuration .
12-09-2008 03:07 PM
Thanks to Giuseppe and Glen.
But I am afraid it's the case this time. All of our switches have switchport trunk mode configured on the trunking ports.
However, I did find something interesting. We have two pair of 6509s. Each pair has its port channel. And only one of the switch in each pair has VTP V2 Mode enable while the other one disable. Does it have anything to do with this issue?
12-09-2008 03:19 PM
Here is the info related to transparent mode
Transparent-VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements, but transparent switches do forward VTP advertisements that they receive out their trunk ports in VTP Version 2.
I am not sure if the port channel issue related to VTP V2 Mode enable or not.
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