So, I can't seem to find a definitive answer to this...

[kidzer]

...and I'm hoping the hive mind of Hexus might be able to help.

Right, so VLAN 1 is by default the Native VLAN on Cisco kit (and most others, I'd imagine - haven't used much else though so I can't be sure), and is used to sent control traffic (CDP/VTP/DTP/etc) between devices.

This means that, by default, this traffic will cross links untagged as VLAN 1 is the Native VLAN on trunks with Cisco kit.

What I'm struggling to work out is this;

If I configure a trunk link and set another VLAN as the Native VLAN (say, VLAN 10) then this means that VLAN 1 will cross the link as tagged traffic. If I then prune all VLANs other than 10 from that trunk link ('switchport trunk allowed vlan 10') then it effectively becomes an Access link on VLAN 10.

Now, back to that control traffic. Does it always use VLAN 1, or the Native VLAN on each link? Furthermore, does VLAN 1 get special treatment with regards to pruning it from trunks - does it always get across a trunk to carry the control traffic?

I've found bits and pieces, but I can't find a complete answer to this...over to you!

[funkymunky]

You can prune VLAN 1 from trunks however it only actually stops user traffic - CDP, VTP and some other protocols will still be sent in a frame tagged with VLAN 1, you can't get rid of it short of disabling the protocol. Some other control traffic such as DTP is sent using the native VLAN i.e. untagged. So yes, certain protocols always use VLAN 1 even if you try and prune it.

[kidzer]

I was leaning towards that viewpoint after troubleshooting some policy drop issues on an ASA 5505, it was what originally prompted me to ask the question.

Cheers!

>.<