[j-nsp] MTU problems over VPLS

[Luca Salvatore]

I have a few sites connected via a VPLS core.  The core devices are all MX 10 routers connected via 10Gb fibre.
I'm having problems doing file copies (SCP between two Centos VMs).

The issue is that the file copy never gets anywhere, on the Centos CLI it sits at 0% then says 'stalled'
To fix this issue I have just set the MTU on the Centos machines to be 1400 - when this is in place the copy works and I get nice speeds.

I don't believe I should have to modify the MTU though, shouldn't path MTU discovery take care of this?

For example - I have done some TCPdumps, I can see the sender is sending traffic with the DF bit set, however I don't see any 'ICMP fragmentation needed' coming back from the MX saying the MTU is too big, I assume this should be the case.

I haven't modified any of the MTU's on the MX, everything is just the default.

I also have normal layer 3 running over the fibre between the routers and when I use that I don't see any issues, so it must be something to do with VPLS.

Any thoughts would be greatly appreciated.

Thanks
Luca.