Connection hangs over CGNAT (Starlink)

[Nikolay Kichukov]

Hi folks,

I am getting similar experience (though it looks like different
underlying problem) on iOS 12 device running latest wireguard
application using cellular (LTE) network for the VPN tunnel.

Very randomly, it may be from a couple of days up to at most 4 days with
the VPN being active the server peer stops receiving the keepalive
packets because the tunnel has become inactive in wireguard client. It
then requires manual interaction to enable it which then connects
instantly.

tcpdump on the server peer does not indicate any incoming traffic when
it happens, so it is most likely a iOS client component crash.

Cheers,
-N

On Fri, 2022-12-30 at 20:08 -0500, Nikolay Martynov wrote:
> 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!
> > > 
> > > 
> > 
> 
>