I am getting MTU problems with connections to my web host provider. The issue is that I am behind ppoe with MTU size set to 1492 which preventing me from using 'scp'. Once changing MTU from 1492 to 1500 the scp works fine however most of other connections do not. Neither web hosting provider nor internet provider confirm blocking of ICMP traffic. Is there any way to check who (which ip on the way) blocks ICMP?
Thanks
ICMP Troubleshooting – How to Check Who Blocks ICMP During MTU Path Negotiation
icmpmtu
Best Answer
MTU is a link-local issue in terms of 'works' vs. 'doesn't work'. If the machines on both ends are configured to use an MTU appropriate to their specific link, then the routers in the middle should fragment packets as appropriate to get data through. Performance will suffer, but you should get traffic, even if ICMPs are being blocked in the middle.
Of course this won't happen if the routers between have one or more links with a misconfigured MTU, but someone would probably have noticed that before now.
As far as checking where / if ICMP is blocked, I suggest traceroute. If you're using Linux, the most recent version in Ubuntu comes with a moderately detailed description of ICMP blocking related issues, and it should give you a good clue as to where the block is coming from. Since you have access on both sides, you should be able to verify in each direction.