MikroTik RB951-2n - possible MTU issue on FTTC

Hello,

Does anyone here have experience of setting up a MikroTik RB951-2n on FTTC with an Openreach modem?

The issue I am experiencing looks a lot like an MTU issue in as far as I can't seem to browse to some websites that I know work, these aren't HTTPS sites so it is a bit weird.

Anyway, I have been playing with multiple MTU settings and it doesn't seem to make a difference, however I connected my laptop to the OR modem and created a connection in DUN and these websites work - using non fragmented pings from here I found the maximum packet size I could use was 1272 which seems odd.

Anyway, any help or suggestions would be greatly appreciated.

Which provider? 1272 sounds very odd, it may be the PC is oddly configured which is compounding the issue with the router.

Zen is the ISP, something I can look into when I get home but don't believe that there should be any weird settings.