[c-nsp] ip tcp adjust-mss

Peter Rathlev peter at rathlev.dk
Mon Feb 11 15:25:58 EST 2013

On Mon, 2013-02-11 at 11:56 -0800, Eric A Louie wrote:
> I just put in this command on my upstream interfaces to help my mpls
> network pass traffic - that is, my effort to eliminate fragmentation
> in my backbone.
> Is anyone else using this method of "mtu control"?  I need some
> support - my CEO is asking why I have to do this, and who else does
> it, and is it a common practice, etc, so I'm looking for evidence,
> more than just "The Cisco TAC told me to do it".

The correct thing to do is make sure you have high enough MTU on all
links. If all your backbone connections are your own at L2 and above you
can just adjust the interface MTU upwards instead.

TCP MSS adjusting only works for TCP and probably puts an extra load on
the CPU of the router.

When doing IPsec or GRE tunnels then MSS adjusting might be prudent but
not in a "backbone", even though that term might mean many things. :-)


More information about the cisco-nsp mailing list