[c-nsp] MTU size with EoMPLS

[The Father]

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