I've got a hub-and-spoke arrangement between 4 development L009's with RouterOS 7.23.1, one as an L2TPv3 server and three as L2TP-ether clients. The interfaces work fine and can pass traffic.
Unlike "regular" L2TP connections however, the server does not list the interface in the l2tp-server menu and I can't find a way to refer to them in a static manner, and hence you can't add them directly to a bridge or to an interface list; in fact there's very little that indicates a client is connected at all:
The only way I've found is by tabbing at interface= prompts or by turning on L2TP logs specifically:
You can add the dynamic entries to a list, but as they can change there's very little point in it and you just end up with a load of red dereferenced pointers.
The only way I've found to reference the connections so far with any kind of reliability is using the built-in "dynamic" interface list, which in this use case is fine, but seems like I'm either missing something obvious or the feature is incomplete.
In profiles, there are bunch of things you can do to a connection connected to the profile.
Add it to a bridge, attach it to an interface list, address list.
Thanks for the suggestion, but unfortunately not: Giving the profile an interface list name and / or a bridge name, then setting that as the L2TP server default profile doesn't do anything as, AFAIK, it's not using a PPP profile when in -ether mode.
As such, all the useful stuff in the profile never gets triggered. "Standard" L2TP-client, yes, but not with -ether.
As mentioned in @rplant's answer above, that works fine if the PPP profile is invoked, but it isn't. On the l2tp-ether client-side, there isn't even a username field! Everything you and @rplant have suggested works fine, as long as you're not using l2tp-ether but l2tp-client instead.
Does L2TP(v3) even allow you to circumvent PPP? I think not since the server requires a PPP profile. If you want to (assumingly) use it only as a transparent L2 link, why not use EoIP?
