google path mtu?

Mikael Abrahamsson swmike at
Fri Jan 23 06:56:09 CET 2015

On Fri, 23 Jan 2015, Lorenzo Colitti wrote:

> Thanks for reporting this. What was the effect? Connections just getting
> stuck? Was there fallback to IPv4?

I would get all the CSS, comments etc, the player would start to try to 
load the video stream, but there would be no video loaded at all (ie the 
progress bar never moved).

> Personally I don't understand why everyone behind a manually-configured
> tunnel doesn't set the MTU in the RA to the MTU of the tunnel... but that's
> not an excuse for things not working.

I did that before, but I can't do it in my Airport Express. I have been 
considering changing my IPv6 tunneling to another device.

However, I have no clue why my OSX box thought it couldn't send 1350 byte 
sized UDP packets to the Internet. Could Google have sent me PTB=1280 from 
this host, so my OSX box thinks it can't send them unfragmented?

Anyone know how I can check in OSX for what destinations it has received 
PTB packets and what the PMTU it think it has for these destionations?

Mikael Abrahamsson    email: swmike at

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