Re: IPv4 specific issue with USB tethering between my Debian laptop and my phone
On 2021-12-17 07:09:52 +0000, Tim Woodall wrote:
> On Fri, 17 Dec 2021, Vincent Lefevre wrote:
>
> > Dan Ritter wrote:
> > > ip link set USBNET0 mtu 1450, or something like that. I don't
> > > know NetworkManager's syntax for that; random googling suggests
> > > that they at least had a historical problem with not being able
> > > to set MTU on anything other than a pure ethernet or wifi link,
> > > but perhaps they've solved that?
> >
> > "ip link" works on its side. I can see with wireshark that something
> > like "ip link set usb0 mtu 1300" is honored, but this doesn't solve
> > the problem (I've tried various values from 1000 to 1450).
> >
> > Note that I could also see with wireshark that the iptables rules
> > with --clamp-mss-to-pmtu did not change the packet lengths.
> >
>
> Does this happen on any connection or just some?
On any IPv4 connection (tested with ssh to 2 remote machines, and
with https on various web servers). IPv6 connections seem fine.
> You said you could reproduce using ssh? Does that mean you can run
> wireshark on both ends and see which packet is getting lost?
I haven't tried wireshark on the other end. I wonder whether there
is a replacement tool that doesn't need an X11 connection, to just
do the capture of the packets.
> Did you try setting both mtu on the interface to something smallish
> plus --clamp-mss-to-pmtu?
I've just tried, and this doesn't solve the problem.
> I'm pretty sure all ipv4 over mobile (which I think is what you are
> testing) depends on NAT. So my other guess of a dodgy NAT device isn't
> impossible. IIRC your ping tests suggested that ipv4 is being tunnelled
> in ipv6
Where would be the issue?
--
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
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