[c-nsp] TCP Throughput / MTU problem ? with Cisco 7304 andMPLSVPN's

[Peter Rathlev]

On Fri, 2008-01-11 at 12:07 -0500, Eric Kagan wrote:
> > Sometimes the controllers allow larger packets to be sent, but there's
> > no guarantee. Would there be any problems associated with adjusting
> > interface MTU up everywhere? Any limits on the data link layer?
> 
> I wasn't sure if there would be any ill effect on non-MPLS traffic and since
> I had not changed it on the 7206's I figured there was some other issue.
> There are no limits, I will try that, thanks.  

You should never experience any negative impact when raising MTU, unless
your data link layer cannot cope. On the contrary even.


> > Can you see at what packet size the router stops forwarding traffic?
> > With different size pings from the access-side for example.
>  
> It allows 1500, not 1501 or larger.....

And that's through the 7304, not from it? That's strange, normally the
clients sit on a 1500 byte MTU connection themselves, and thus should
have no problems if path MTU is 1500 or greater. If you have a Linux-box
on the client side the "tracepath" command can give you the Path MTU
(smallest MTU along the path) and show you whichs hops have what MTUs.

Anyways, adjusting the interface MTU should help. :-)

Regards,
Peter