Re: [nsp] MPLS issues with MTU

From: Félix Izquierdo (
Date: Wed Nov 14 2001 - 12:33:18 EST wrote:
> In the Cisco Press book on MPLS, it mentions that if you're doing MPLS on
> routers that communicate via a catalyst ethernet switch, you may need to
> contact TAC for a workaround that enables the switch to handle the
> oversized packets caused by tagged packets. I ran into this problem this
> morning with a 3640 talking to a 7206 via a 2924xl-en (the 2924xl-en is
> actually doing VLANS & ISL with the 7206).
> The workaround I've come up with is to set the MTU on the switch ports
> involved higher. Is that the correct solution?

I'm in the same situation with a 2924XL ( running 12.0(5.4)WC(1) ).
Configuring mtu 1504 in the switch port where the labeled packets are
recieved, the packets are switched but I see input errors in the "show
interface" output and Oversized frames in the "show controller" output.
The mtu command for XL switches is not documented and I don't know the
maximum value. ( I dont't know why the command is called MTU, in this
case we are configuring the MRU ).

I think that other workaround is to configure the port like a 802.1q
trunk port, and using only the native vlan.



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