[c-nsp] MTU size with EoMPLS
The Father
lobo at allstream.net
Fri Feb 29 13:21:07 EST 2008
Hi group. I'm wondering if someone can help me out with a bit of an MTU
issue I'm seeing when playing around with EoMPLS in our lab.
This is the topology I have setup:
3550-24------3750-----7603/Sup32-------1811-------7206VXR-NPE300-----3750------3550-24
LDP is enabled between the 7600, 1811 and 7200 (yes it's an 1811 as my P
for now). I have created VLAN 800 on the first 3550 and used the
xconnect command on the ingress Gig interface of the 7603 (sub-interface
is used). The circuit is encapsulated and sent over to the 7206VXR
(sub-interface used here too). From there it is sent over to the other
3550 (obviously trunking is being done between the 3550s and 3750s). We
have also created SVIs on the 3550s to act as our layer 3 interfaces
with IPs.
When we try and ping from one end to the other with 1500 byte sized
packets it fails. The highest we can go is 1478. I know that with MPLS
you normally are required to enable jumbo frame support but where
exactly would I do this? Is it on the interfaces that have LDP enabled
on them or in the entire network I have setup above? Currently
everything is set to the default of 1500.
Another thing that I'm confused about is when to use the "mpls mtu xxx"
command. If I understand it correctly, you must have the interface MTU
set higher than the MPLS MTU. I have tried using the "mpls mtu 1520"
command on the LDP enabled interfaces but it has made no
difference...probably because the interface MTU is still 1500.
Any thoughts or advice on trying to resolve this?
Thanks.
Jose
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