VTP Pruning & 802.1Q Devices

[jason.chin]

Hi, i would like to impliment VTP Pruning on my VTP Management Domain however I would like to confirm that unless i have a port configured as access for a specified VLAN, that VLAN will be pruned. Here is why i ask, i have devices that do their own 802.1Q VLAN tagging jacked into switch ports configured as dot1Q Trunks (Assume VLAN 15). I do not have any switch ports configured as switchport access vlan 15 on the switch. Will VLAN 15 be pruned and traffic to and from VLAN 15 blocked?

[pkhatri]

Hi,

That depends on whether the switch has other switches hanging off it that have access ports in VLAN 15. For example, say you have the following setup: SwA - SwB -- SwC

If there are no access ports for VLAN 15 in SwA, that VLAN will be pruned off the trunk between SwA and SwB. Now, given another scenario where there are no access ports for VLAN 15 in SwB, but there are access ports for VLAN 15 in SwA, SwB will not prune VLAN 15 off the trunk to SwC.

Hope that helps - pls do rate the post if it does.

Paresh

[jason.chin]

Hi Paresh, thanks for the quick reply.

So a switch has to have an access port in vlan-15 or another switch below it that has an access port in vlan-15 otherwise VLAN-15 will be pruned. The Switch will not detect the 802.1q vlan-15 frames sent by a third party device connected to one of its dot1q trunk ports and not prune vlan-15.

[pkhatri · Accepted solution]

Yes. What you can do, of course, is to make VLAN 15 pruning-ineligible. If you do that, it will not get pruned.

Paresh

[sundar.palaniappan]

Hi,

I assume vlan 15 is the native vlan on those dot1q trunks and if that's the case then vlan 15 will NOT be pruned. As the remote switch configured as dot1q trunk, with a native vlan of 15, will include vlan 15 as ineligible for pruning in the VTP messages to the other switches in the domain.

Hope that helps!

Regards,

Sundar

[jason.chin]

Hi Sundar, the Native VLAN is VLAN-1.