Configure GRE Tunnel on 3560 switch

Unanswered Question
Feb 18th, 2010

Hi

I currently have a GRE tunnel terminating on 2xold 3640 routers which I am to replace with 3560 switches.

The current tunnel has an 'ip mtu size' of 1476 to allow for the GRE header of 24 bytes. Initial testing has indicated the MTU size is not configurable on the tunnel interface of the 3560 - could someone please explain how the 3560 switch forwards packets with a max 1500 bytes MTU across the tunnel?

Any help greatly appreciated!

I have this problem too.
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Giuseppe Larosa Thu, 02/18/2010 - 02:54

Hello Curtis03,

be aware that a GRE tunnel is supported only on software on a low end multilayer  switch like C3560.

>> could someone please explain how the 3560 switch forwards packets with a max 1500 bytes MTU across the tunnel?

the resulting GRE packet will be fragmented in software as any other GRE packet.

Hope to help

Giuseppe

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