Re: [Linphone-users] How to tell linphone which IP address to use

[Brian J. Murrell]

On 12-02-21 05:52 PM, Koos Pol wrote:
> 
> You don't get to choose an IP address. That is a function of the network
> stack.

But within the Session Initiation protocol by way of the Session
Description Protocol each end informs the other end of which IP address
and port that it should be trying to establish the RTP session with.  So
it's the actual SIP implementation that is choosing an IP address to
include in that SDP message.

So to be clear we are not talking about the selection of IP addresses on
the packets that leave the machine headed out for the remote machine.
Yes, you are correct.  Those are selected by the network stack.

The address that's written into the SDP is not chosen by the network
stack and that is the address that is typically wrong on a configuration
where a machine is on a public network (i.e. the Internet) and has a VPN
connection on top of that public network, effectively giving the host
two interfaces and two addresses.

What linphone needs to be doing is effectively:

$ ip route get 10.75.22.8

and then extracting what the source ip address for that route will be
out of the answer.  For example:

10.75.22.8 via 10.8.0.13 dev tun0 src 10.8.0.14
                                      ^^^^^^^^^
The address that should go into the SDP is therefore 10.8.0.15, not the
address that will be on typically eth0 or wlan0, etc., which seems to be
the address linphone most frequently uses.

Cheers,
b.

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