Connection hangs over CGNAT (Starlink)

[Nikolay Martynov]

Hi!

FWIW, reducing MTU doesn't seem to help. Also it looks like I almost
never experience this on a cell network and experience this sometimes
multiple times in an hour on startlink.
At any rate the problem can easily be simulated by just using
iptables. If for whatever reason packets are cut on the return path
for an established connection a new connection (with new source port)
is not reestablished resulting in connection effectively hanging
forever. I do not want to sound too presumptuous, but this seems like
a clear bug to me.

On Sun, Dec 18, 2022 at 10:41 PM Dean Davis <dean_davis at withtel.com.au> wrote:
>
> hi
>
>
> same issue
>
>
> I do kind of a automated ping test and if fails on the server side to
> many times bring down interface and then back up in a bash script
>
> with
>
> nmcli connection down wg0 && nmcli connection up wg0
>
>
> to me it looks to be connection state issue difference between new and
> established/related  ( can not confirm )
>
>
> ugly but works for me
>
>
>
> regards
> dean
>
>
> On Thu, 2022-12-15 at 21:12 -0500, Nikolay Martynov wrote:
> > Hi!
> >
> > I'm experiencing strange behaviour with wireguard: from time to time
> > connection 'freezes'.
> > Most often I'm observing this on an Android phone when connected from
> > my home over Starlink.
> > Server: latest Openwrt, Client: latest Android app.
> > The connection establishes and works fine for some time. After some
> > time the client still shows connection is established, but no
> > incoming
> > data is coming.
> > On a server side 'latest handshake' goes into hours/days.
> > The freeze happens randomly, for no apparent reason and I think only
> > over starlink. I do not think I have ever observed this problem on
> > cell networks.
> >
> > Reconnection solves the problem immediately.
> > I did some tcpdumping when the problem was present and found the
> > following:
> > * Server side sees incoming traffic from the client and sends
> > responses.
> > * On my own router connected to Starlink (i.e. interface between my
> > router and Starlink router) I see data going from the client to the
> > server - but no packets coming back.
> >
> > So my 'hypothesis' is that somehow Starlink's CGNAT 'forgets' one
> > side
> > of the connection - and so data continues to go in one direction, but
> > it doesn't come back. The thing with the wireguard is that it looks
> > like it doesn't change the outgoing port when it attempts to do
> > another handshake. This means that it continues using the same 'half
> > broken' connection forever.
> >
> > I think the same happens to me at least once on a Linux client - but
> > the difference with the phone is that the phone is always on and
> > therefore the duration of the connection is much longer.
> >
> > I tried experimenting with keepalive messages - but it looks like
> > they
> > make no difference. Once connection freezes I see keepalived arriving
> > onto the server, server sending reply - but that reply never arrives
> > to the client.
> >
> > It looks like the solution to this problem would be for the client to
> > use a different outgoing port when sending a handshake but I was not
> > able to find an option for that.
> >
> > Is this something that is possible to do?
> > Thanks!
> >
> >
>


-- 
Martynov Nikolay.
Email: mar.kolya at gmail.com