From: Ryan (ryan95842@gmail.com)
Date: Thu Jul 19 2007 - 22:54:04 ART
Does anyone have a good document on MPLS MTU settings?
I'm trying to understand the whole MTU/MSS relationship with MPLS.
From what I can figure out, one needs to increase the MTU on links that
support MPLS to support the MPLS labels (4 bytes per label).
So on a PE to P link, one might increase the MTU to 1508 (or 1512 to support
EoMPLS QnQ?). This is fine for IOS that supports 'mpls mtu xxx' command or
GE interfaces or switches where the MTU can be changed. But on a
FastEthernet interface where the MTU can not be changed, do I adjust the the
MSS value down 12 bytes? (1460-12)
What about PMTUD?
What about BGP peers? If I'm peering across MPLS and I want to improve my
convergence performance of my BGP peers, if I've increased the MTU to 1512
for MPLS for example, will the PMTUD take into account the MPLS labels? or
do I need to manually set the MSS on each of the links?
Thanks for any response...
-Ryan
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