"unsupported" features in IOS ("mpls mtu") (was: Re: [c-nsp] High Availability PoP Design)

Everton da Silva Marques everton at lab.ipaccess.diveo.net.br
Fri Nov 4 13:01:19 EST 2005


On Fri, Nov 04, 2005 at 12:31:21PM -0500, Rodney Dunn wrote:
> We support 1500 byte ip headers on those PA's +
> 6 labels (24) bytes.
> That is minus the ethernet/dot1 headers.
> The problem was we originally didn't do per bounds checking
> on each filed (it's too performance impacting).
> It's an extremely complicated set of things on how and
> when fragmentation is done.
> People thought the tag mtu command was doing something it wasn't
> in the first place so that's why we changed it.

We run "mpls mtu 1516" on some 7500 routers
with IOS 12.0S, like this:

  7513-1#sh run int FastEthernet5/0/0 | i tag
   tag-switching mtu 1516
   tag-switching ip

If memory serves me correctly, we were advised by
TAC to use the command to circumvent fragmentation

Is that command being removed from 12.0S as well?
If so, what is going to be the new proper setting?
Just to remove the "mpls mtu" command from the


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