dot1q tunneling questions

[christian.pinedo]

Hello,

I'm new to dot1q-tunneling so these are my questions:

- Cisco Catalyst 2960 supports "switchport mode dot1q-tunnel" ? I think that 3750 yes... but I'm also not sure. The support of "dot1q-tunnel" is related to IOS version or to platform??

- If a switch doesn't support dot1q-tunnel, will it be able to forward Q-in-Q traffic? I think so, it would have provideer-VLANs configured and it won't realize that it's Q-in-Q traffic but it couldn't have tunnel ports for ingress and egress customer traffic. Am I right??

Thanks,

Christian

[Leo Laohoo]

2940/2950/2955, 2960 support only 802.1Q.  3560, 3750 support 802.1Q and ISL.

[christian.pinedo]

Thank you but my question was about Q-in-Q also know in Cisco as dot1Q tunnel... Anybody can answer me?

[Kishore Chennupati]

hi christian,

- Cisco Catalyst 2960 supports "switchport mode dot1q-tunnel" ? I think that 3750 yes... but I'm also not sure. The support of "dot1q-tunnel" is related to IOS version or to platform??  

As far as I have seen this  is supported almost on all switching platforms.What you can do is to  read the release notes of the IOS and also the platform you have or check it on the cisco  feature navigator tool.

- If a switch doesn't support dot1q-tunnel, will it be able to forward Q-in-Q traffic? I think so, it would have provideer-VLANs configured and it won't realize that it's Q-in-Q traffic but it couldn't have tunnel ports for ingress and egress customer traffic. Am I right?? 

Hi, dot1q tunnel is usuallly configured on the ingress and egress of the provider network. once the frames from the customers (C-tag) are tagged with the provider vlan (S-tag). this is just like a normal tagged frame inside the provider network. Allow me to explain this further.

   CESW1-----PESW1-----PESW2------PESW3-----CESW2

in the above case the dot1q tunnel ports wil be on PESW1 and PESW3 facing the CE's. the middle switch PESW2 doesnt need to support dot1q tunneling.It just receives a tagged frame from PESW1 and PESW2 and just trunks it.

Hope this gives u some idea. Please let me knw if u need to know more

Regards

Kishore

[christian.pinedo]

Thank you for the answer Kishore.

I have been testing Q-in-Q and as you say the provideer switches don't need to know Q-in-Q to be able to transport provideer-VLANs in mode trunk. The only recommendation is to increase the MTU of all switches (CPE switches that must encapsulate customer VLANs and the core switches that transport the service VLANS) to 1504 bytes at least.

Regards,

Christian

[Kishore Chennupati]

Thanks for the generous ratings. Yes, you are right MTU is defintely a consideration when doing double-tagging etc.

Normally the providers have enough room(jumbo frames 9216bytes) on their interfaces to support different overheads.etc

Regards,

Kishore