A simple question (hopefully) but with no clear answers when doing a Google Search. What is the MTU of VDSL (not VDSL2)? With ADSL it was 1492, but most ISPs added PPPoE/PPPoA headers reducing it to 1452, is this still the same when it comes to other types of DSL (including VDSL)?
You can check the MTU yourself using ping. Have a look at this page.
If you receive an error similar to this:
Then, your MTU has been exceeded. You can try a smaller value until get a different response.
You can check the PPPoE RFC. It says the maximum MTU is 1492 as you said.