Ping an ICMP target with the following command:

ping -c 2 -s 1472 -D   

This should succeed or it should return Frag needed and DF set (mtu = 1492).
If either of these are true, stop, connection works just fine.

If this does not return anything, or gives a timeout message then:

traceroute -F 1472   

Whichever is the last hop to respond is the last one that is working correctly.
If no respond at all it’s CPE.