[toast0]

You also need to make changes on the PPPoE server, which is hard because if a provider is running PPPoE in 2023, they probably don't care about doing things well (but maybe I'm just bitter about CenturyLink)

I have a browser based mtu test http://pmtud.enslaves.us/

Currently IPv4 only, requires a somewhat recent browser, and client to server testing is iffy, but if you start the test and get OK in the notes field for both directions, your MTU settings are probably fine (or something is doing proper mss clamping between your client and my server, my server is limited to 1500 MTU so problems with jumbograms can't be detected)

[ta1243]

I think openreach requires all their customers to use pppoe - certainly I've had it with both BT and A&A