Q in Q through an unsupported switch - Will it work?

[Difan Zhao]

Hi experts,

I need to build a tunnel to bridge a demo network in the two buildings (West and East). Currently the cables between the buildings are used by the office network. I don't want the demo network to be part of the office network so I'm thinking about using the QinQ feature.

In the East building I have a C4506 Core however it doesn't support QinQ. In the west building the access switch 3750 supports it. I'm thinking maybe I can use an extra switch (very likely to be a 3560). However will the QinQ work through an unsupported C4506 switch? The connection will be like:

             West building                                                                             East building

Demo network switch1 --- C3750 --------------------------- C4506 --- C3560 --- Demo network switch2

Will the 4506 have a problem with the double tagging?

thanks!

[Thotsaphon Lueangwattanaphong]

Hi,

  If I understand your question correct, C4506 just knows about PE-VLAN. No need to do Q-in-Q because you're going to do it on C3750 and C3560. C4506 is in between. It should be fine. However,you need to check the MTU on C4506 as well. It has to be 1504 bytes for Q-in-Q environment.

HTH,

Toshi

[Difan Zhao]

Hi Toshi,

Thanks for the reply! Sorry for my bad description. It's very good point about changing the MTU on the Core. However what about the CRC checksum? Will they be affected because of the extra VLAN tag?

Thanks,

Difan

[Thotsaphon Lueangwattanaphong · Accepted solution]

Hi,

   MTU is only what we are concerned about C4506. It would be fine when receiving tagged packets(PE-VLAN) on trunk interfaces.

HTH,

Toshi

[Difan Zhao]

Thanks a lot Toshi! I will give it a try.