MTU to CDN's

Mikael Abrahamsson swmike at
Fri Jan 19 14:05:17 UTC 2018

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 at

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