google path mtu?

Ignatios Souvatzis ignatios at
Mon Jan 26 10:58:17 CET 2015


On Fri, Jan 23, 2015 at 07:32:47AM +0100, Tore Anderson wrote:
> * Mikael Abrahamsson <swmike at>
> > So I guess the problem this time was some Google servers sending me 
> > PTB=1280 and then Chrome not taking this into account when sending
> > UDP packets when using QUIC, resulting in fragmented IPv6 packets
> > (which works very badly in real life), and then not handling this
> > situation by doing fall-back to something else.
> I highly doubt that Google would be sending you PTBs. 10 SEK says it's
> your tunnel ingress router (i.e., your Airport Express)...

Wrong direction for getting video from Google, isn't it? That is,
the other end of the tunnel would have to send PTB's successfully
to Google to make Google send you smaller _data segments_.

This is why setting the MTU (maximum _transmission_ unit) at your
end doesn't necessarily help.  You'll have to lower your OS's notion
of maximum TCP segment size negotiated for TCP reception.

And you can't do anyhing at all for incoming UDP-transported
data streams on the receiving side (unless the higher protocol
has some way to do it).


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