Re: IPv4 specific issue with USB tethering between my Debian laptop and my phone

[Vincent Lefevre <vincent@vinc17.net>]

On 2021-12-15 06:09:12 +0000, Tim Woodall wrote:
> On Tue, 14 Dec 2021, Dan Ritter wrote:
> 
> > Vincent Lefevre wrote:
> > > Hi,
> > > 
> > > When I use USB tethering between my Debian/unstable laptop and my
> > > Samsung Galaxy Note10+ phone (Android 11), everything is OK with
> > > IPv6 connections (e.g. "wget -6"), but IPv4 connections freeze
> > > (e.g. "wget -4" or "ssh -4"). I can notice this in particular when
> > > testing with the same remote server. For instance, with "wget -4",
> > > a few dozens of KB are downloaded, then the connection is completely
> > > frozen.
> > > 
> > > I don't have any issue with the mobile hotspot (thus wifi between the
> > > laptop and the phone) or with a Cosmo under Android 9 (instead of the
> > > Samsung Galaxy Note10+), but in both cases, this is much slower, and
> > > I sometimes get wifi disconnections.
> > > 
> > > On my Debian laptop, I'm using NetworkManager (nmcli).
> > 
> > Have you investigated the MTU? This sounds like a mismatch
> > between what your laptop and phone are using.
> > 
> > Diagnosis (besides looking at connection details on both sides):
> > ping with increasingly large packet sizes. If it works at small
> > IPv4 packet sizes and then stops, that's the problem.

Indeed, this works up to
  ping -4 -s 1472 joooj.vinc17.net
  ping -6 -s 1452 joooj.vinc17.net

> Yes, probably - --clamp-mss-to-ptmu in iptables might be what is needed.

Thanks, but taking the rules from

  https://tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.cookbook.mtu-mss.html

I've tried

  iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

and

  iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1024

and none of them have any effect. Or did I need something else?

Any other suggestion?

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)