Wouldn't those situations be causing issues now, given the likelihood that someone with a less than 1,500 byte MTU is communicating with you now? ----- Mike Hammett Intelligent Computing Solutions http://www.ics-il.com Midwest-IX http://www.midwest-ix.com ----- Original Message ----- From: "Mikael Abrahamsson" <swmike@swm.pp.se> To: "Mike Hammett" <nanog@ics-il.net> Cc: "NANOG list" <nanog@nanog.org> Sent: Friday, January 19, 2018 8:05:17 AM Subject: Re: MTU to CDN's On Fri, 19 Jan 2018, Mike Hammett wrote:
Other than people improperly blocking ICMP, when does PMTUD not work? Honest question, not troll.
Mismatch of MTU interface settings between interfaces, mismatch of MTU between L3 devices and intermediate L2 devices, anycast services, ECMP based services where the ICMP error is delivered to the wrong node. So yes, there are plenty reasons that PMTUD doesn't work without anyone doing it because of ill will or incompetence. -- Mikael Abrahamsson email: swmike@swm.pp.se