EoIP over L2TP: MTU problem?

RouterOS Beginner Basics
1

I got an EoIP tunnel working over L2TP, sort of. The symptom I believe I’m seeing is that large packets don’t make it across.

on a unix box, ping -s 1390 [remote host] works, but 1391 fails.

I would expect the EoIP tunnel itself to be able to properly fragment the packets going across the link. Is this not so?

2

Setting MRRU 1600 on both ends fixed it. I also switched the connection over to BCP bridging instead of EoIP.