[c-nsp] MPLS MTU / Jumbo frames etc.

[Gert Doering]

Hi,

On Wed, Jul 22, 2009 at 02:16:29PM -0400, Brandon Applegate wrote:
> Scenario 3 really gets me though.  Why doesnt it complain and tell me icmp 
> frag to 9212 or something ?  Isnt the frame 9220 when it's all said and 
> done ?  Is the router fragmenting this in software at the 'mpls level' and 
> just not telling me ?  Should I set mtu down to 9212 or something to make 
> sure that the router NEVER frags frames ?

I'd bet that the linux box is not sending full-sized 9220 packets, but
fragmenting inside.

Unless the linux box has 10GE to the router, and is allowed to use full
9220 MTU (via ifconfig and/or "ip route"), it will send 1500 byte fragments.

So the router will never have to worry on whether or not the linux packet
+ MPLS overhead will fit into its MTU...

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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