[c-nsp] MPLS, MTU and POS (STM-1) "problems"

[Primoz Jeroncic]

Hi everyone

I know I'm probably missing something really basic here, but at 10pm after
bugging with this for whole day my mind is probably not really clear
anymore :)
My core was pure IPv4 before and after turning on MPLS I have few
strange problems. Current config (really short and stripped one) could
look like this (sorry for my ascii "art"):
CE1
|
PE1(c2811)
|
P1 (c7206vxr) -- PE2(c7401) -- CE2
|
P2 (gsr) -- P3 (gsr) -- PE3 -- CE3
|
P4 (gsr)

All connections between CE's, PE's and P's are fastethernet or gigabitethernet
links, except between P2 and P4 where I have STM-1. I have also normal (ipv4)
clients connected to all PE and P's. Now I have some strange problem (at
least for me at this time of day). When I try to ping with 1500bytes/packet
(and DF bit set to 1) from any client it works fine from client (ipv4 client
not CE) all the way to P3. But when I try to ping P4 (over STM-1) it doesn't
go. When i set route-map which sets DF bit to 0 on ingress port from client to
my router it works (which is right anyway). Only problem I have with this is,
that I can't set those route-maps on every single ingress port I have all over
my network.
I would also understand this won't work if it would be constant all the way
through network, but not that only problem is on STM-1 link (with MTU set to 4470
bytes) while on ethernet links everything is working fine.
I would appreciate if someone can suggest some solution or at least tell me
it's normal that it doesn't work :)

Thanks guys for your help.

Have nice day
Primoz Jeroncic
Support - IP Connectivity & Routing
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