Re: I've got a bad feeling about this...
"They announced last year that they are stopping the trails due to core infrastructure upgrade. Still no word on when new trails will start up again."
The IETF doesn't understand networks, which is why calls from netheads to de-fund the ITU get amusing. The ITU develop global standards, which is why the Internet works. Buy an STM-64 or an OTU-2 pretty much anywhere in the world and you'll get the same thing, and how it works is pretty tightly defined. Netheads however like Ethernet, because Ethernet is perceived as cheap. Which it can be, if you know what you're buying.
If you're buying it for xDSL backhaul, knowing about MTU size is important if your IP traffic is turned into PPOE and carried over an L2TP tunnel over an Ethernet. Which is a bunch of extra header bytes that may not fit in the 'standard' MTU of an Ethernet link. So you get fragmentation, which can be a bad thing. You may get it earlier if your Ethernet is EoMPLS because you need bytes for the MPLS lables as well. That can be.. challenging with v4 networks, especially if they're expecting to be able to send a 1500 byte frame and set the DF bits. Add IPv6 into the mix and your overhead bloats given the address inflation.
But this is OK, because you are not allowed to fragment IPv6 packets at the router. If they're fragmented, they just get dropped and you may or may not become aware of this depending on how well (or badly) PMTUD has been implemented. The IETF workaround is to specify a minimum MTU of 1280 bytes, which may just work on Ethernet links that don't support jumbos, baby jumbos or pink elephants. 1280 is of course less than you get with IPv4, so goodput on large packet transfers will have to drop to ensure delivery. It's less efficient (by a lot with small packets), but that's progress for you.