[j-nsp] MTU problems over VPLS

[Benny Amorsen]

Luca Salvatore <Luca at ninefold.com> writes:

> 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?

VPLS presents a layer 2 link. There is no way for a L2 link to send ICMP
messages.

Fix your VPLS core to present a 1500 byte (or preferably much higher)
MTU or tell the servers what the actual MTU is.


/Benny