Re: OpenVPN suddenly working one way only

> On 7/5/24 11:31, Ronald Klop wrote:
> 
> > Of course this can be a firewall or routing issue somewhere in between 
> > the hosts blocking traffic from B to A.
> 
> Hmm...
> The two hosts can communicate with any other protocol.
> Also the VPN can handshake, so packets are exchanged correctly.
> I'm only using ipfw: no packet is logged as blocked, but, in any case, 
> it blocks after tcpdumps sees them and I don't even see them.
> 
> 
> 
>  > Or both? Can you run tcpdump on the physical interfaces? What
>  > traffic do you see on the openvpn port?
> 
> Let's say, after handshake, I ping A -> B:
> _ A sees the request going out tun;
> _ A sees the UDP packet going out via physical interface;
> _ B sees the UDP packet arriving;
> _ B sees the request coming in via tun;
> _ B sees the answer going out via tun;
> _ B sees the UDP packet going out the physical interface;
> _ A doesn't see the UDP packet coming in (so obviously nothing on tun also).
> 
> 
> 
> > Can you switch to TCP?
> 
> Would be a little work and using OpenVPN/TCP is highly discouraged.
> However, I just changed UDP port and it seems to work!
> 
> I'm puzzled...
> So maybe some system in between my two hosts was blocking packets, 
> but... after the handshake!?!?!?
> Very strange.
> Or host B has some trouble and changing its port helped???

Or host A has a zombie process with a UDP listen on the port?
Often when I have problems with tunnels it is some residual
thing left over from a prior run, like ppp(8) loves to leave
behind named pipes in /var.

> In any case, thanks a lot for answering.
>   bye
> 	av.

-- 
Rod Grimes                                                 rgrimes@freebsd.org