Solved: Native vlan 802.1q and ISL ?

philipbarker · ‎01-30-2008

Hi,

I have a 802.1q trunk and an ISL trunk conigured between two switches.

When I 'sh int trunk' the output shows the native vlan as 1 for both 802.1q AND ISL ?

Does 'native vlan' have any meaning within ISL ? I don't think it does but just need to confirm.

I think I have verified this in the following way:

I changed the native vlan on one end of each trunk (the 802.1q and ISL) respectfully and CDP only complains about NATIVE_VLAN_MISMATCH for the 802.1q trunk.

Regards,

Phil.

Jon Marshall · ‎01-30-2008

Hi Phil

Yes you are correct. ISL tags all frames and does not have a concept of a native vlan as such where the native vlan sends packets that do not have a vlan tag.

The native vlan in 802.1q was designed to allow compatability with older switches that did not support tagged frames.

HTH

Jon

View solution in original post

Jon Marshall · ‎01-30-2008

Hi Phil

Yes you are correct. ISL tags all frames and does not have a concept of a native vlan as such where the native vlan sends packets that do not have a vlan tag.

The native vlan in 802.1q was designed to allow compatability with older switches that did not support tagged frames.

HTH

Jon

srue · ‎01-30-2008

minor correction...ISL doesn't tag, it encapsulates. dot1q tags.

http://www.cisco.com/warp/public/473/741_4.html

Jon Marshall · ‎01-30-2008

thanks :)

srue · ‎01-30-2008

that was mainly for the benefit of the OP..