[c-nsp] 7200 MPLS MTU Issues

[Jon Lewis]

On Tue, 15 Mar 2005, John Osmon wrote:

> On Tue, Mar 15, 2005 at 09:44:22PM -0500, Kenny Stoltz wrote:
> [...]
> > Ironically, cisco claims that the 7200 can /do/ MPLS... This is almost
> > laughable if it can't exceed 1500 bytes.
>
> If you can find way to migrate the links to GigE and/or serial ports,
> the routers should work fine.  If you're stuck with ether/fastE, you may
> need to find another workaround.

Huh?  The 7200 FEs (both IO/FE and PA-FE) handle the 'oversized' MPLS VPN
tagged packets just fine.  You have to configure tag-switching and a
tag-switching MTU on any interface that will be passing tagged packets.
i.e. Try adding
 tag-switching mtu 1520
 tag-switching ip
to your FE interfaces that need to pass MPLS VPN tagged packets.

The next problem you'll run into is switches not wanting to deal with
oversize (giant) packets.  Older software revs on the 2900XL series
wouldn't do it at all.  Fortunately, cisco came up with a fix in later
software revs allowing you to set a larger than 1500 MTU on 2900XL switch
ports.  The packets are still counted as giant errors, but at least they
pass.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
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