MTU to CDN's

Mike Hammett nanog at
Fri Jan 19 14:07:09 UTC 2018

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 


----- Original Message -----

From: "Mikael Abrahamsson" <swmike at> 
To: "Mike Hammett" <nanog at> 
Cc: "NANOG list" <nanog at> 
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 at 

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