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Re: [Linphone-users] Linphone call over SSH tunnel; RTP not connecting

From: Stuart Langridge
Subject: Re: [Linphone-users] Linphone call over SSH tunnel; RTP not connecting
Date: Mon, 31 Jul 2017 12:53:04 +0100
User-agent: Mutt/1.5.24 (2015-08-30)

> Why is machineB only available via SSH?  Firewall?  NAT?

This is the part that isn't changeable, I'm afraid; machineA
and machineB are not accessible to each other, but they do
have access to two SSH machines which _can_ see each other. (For
various reasons I'm not really able to go into we can't use a
"proper" VPN like openvpn either; ssh port forwarding is what's
available. I know this isn't ideal for SIP/RTP calls, yep, and
I appreciate you helping despite that!)

CJDNS would be ideal if we had UDP -- I didn't know about it
at all, and it sounds great -- but it's UDP, so that can't work,
sadly. It sounds like the fixed-rtp-port config option for
linphone will be the way and then forward those ports too. The
problem I have there is this. Imagine that we tell machineA
to use port 9999 as its fixed RTP port. We then use the ssh port
forwards to have machineB port 11111 be forwarded to machineA
port 9999. So machineB can now happily actually talk RTP to
machineA; machineB just needs to believe that it should connect
RTP to localhost:11111 rather than machineA:9999 which it can't
see. But... how does machineB find out that it should use
localhost:11111 as the RTP port? MachineA will tell it "use
machineA:9999 for RTP". Can I have machineA believe that its own
RTP port is "localhost:11111" which will then get sent over in
the SIP headers as the RTP location and then correctly
interpreted by machineB? That is: forwarding the ports is fine
and doable, but I don't know how each end of the connection
knows to use those forwarded ports rather than what it's told...?

(and thank you again; I appreciate that this is swimming against
the tide somewhat!)


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