Mailing List Archive

On Sat, 24 Jan 2015, Andras Toth wrote:

> Airport Express is setting the IPv6 Tunnel MTU to 1280 in all cases and
> it's not configurable, as far as I'm aware.

That is what I have discovered. So the HE.net tunnel termination point
will send PTB=1480 when sent 1500 byte packets, and my airport extreme
will send PTB=1280.

--
Mikael Abrahamsson email: swmike@swm.pp.se

Hi,

On Mon, Jan 26, 2015 at 10:47:51AM +0100, Mikael Abrahamsson wrote:
> On Sat, 24 Jan 2015, Andras Toth wrote:
>
> >Airport Express is setting the IPv6 Tunnel MTU to 1280 in all cases and
> >it's not configurable, as far as I'm aware.
>
> That is what I have discovered. So the HE.net tunnel termination point will
> send PTB=1480

to the outside...

> when sent 1500 byte packets, and my airport extreme will send PTB=1280.

to the inside only, or even to the outside for incoming packets?

-is

Hi,

On Fri, Jan 23, 2015 at 07:32:47AM +0100, Tore Anderson wrote:
> * Mikael Abrahamsson <swmike@swm.pp.se>
>
> > 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).

-is

On Mon, 26 Jan 2015, Ignatios Souvatzis wrote:

>> when sent 1500 byte packets, and my airport extreme will send PTB=1280.
>
> to the inside only, or even to the outside for incoming packets?

Inside only. It'll happily receive 1480 sized tunneled IPv6 packets,
decapsulate and send out to the LAN.

--
Mikael Abrahamsson email: swmike@swm.pp.se

On Mon, 26 Jan 2015, Ignatios Souvatzis wrote:

> 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.

That depends if the QUIC implementation in Chrome will understand path MTU
and send smaller UDP packets than 1350 if needed. In my case it didn't.

--
Mikael Abrahamsson email: swmike@swm.pp.se