MTU for AToM question...

Unanswered Question
Jan 2nd, 2008

Hi:

I have a question regarding AToM.

Say I have CE1---PE1----P1----P2----PE2-----CE2

CE1 to PE1 - Ethernet 802.1Q

CE2 to PE2 - FR

To get AToM up and working, would I need to change the mtu on the PE and P routers in the core?

And if so to what value?

What command would I use, if I had to: mtu or mpls mtu?

Thanks for your help.

Sincerely.

I have this problem too.
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cpubob Thu, 01/03/2008 - 12:20

So you would want to change the mpls mtu on the PE and P routers to accommodate a full ethernet frame plus the two mpls labels and any other additional info, like control words or vlan tag you might be transferring across the backbone, a value like 1514 would work, but if you ever decide to do straight ethernet to ethernet l2vpn with QinQ, then you would be up to 1530. If you maybe did serial links in the future, you'd maybe be up to 4480-4490.

In most SP environments I've worked it, its standard to set the mpls backbone mpls mtu to 9100 or 9192 at install time to remove any issues with the backbone mtu.

Mpls mtu only affects handling of labeled packets, not unlabeled packets.

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