Hi, You can also inspect the SDP and look for private or public IPs and perform some logic based on that. sdp_get_line_startswith("$avp(sdp_media_ip)", "c="); if (is_ip_rfc1918("$(avp(sdp_media_ip){s.select,2, })")) {} The delimiter for the transformation is an empty space in this case. Hope this helps. Regards, Grant From: sr-users &lt;sr-users-bounces(a)lists.kamailio.org&gt; On Behalf Of David Villasmil Sent: donderdag 21 november 2019 09:38 To: Kamailio (SER) - Users Mailing List &lt;sr-users(a)lists.kamailio.org&gt; Subject: Re: [SR-Users] How to retrieve local socket that will be used to send a message from the branch route [EXTERNAL EMAIL] Hello, I'm not sure this is the best or even the right way, but i do that by figuring out where the call is coming from. In my case, an INVITE from an RFC1918 IP address will always be internal to external and vice versa. i.e.: # If the Source IP is an RFC1918 address, it's coming from an internal endpoint, so the call is going out if (is_ip_rfc1918("$si")) { $dlg_var(rtp_direction) = "direction=internal direction=external"; } else { $dlg_var(rtp_direction) = "direction=external direction=internal"; } You may even check both origin and destination domain ($du) and configure rtpengine accordingly. onsend_route { xlog("L_ERR", "[onsend_route] Packet going to $du\n" ); if (is_ip_rfc1918("$si") && is_ip_rfc1918("$du") ) { # call is internal to internal } else if (is_ip_rfc1918("$si") && !is_ip_rfc1918("$du")) { # call is internal to external } else if (!is_ip_rfc1918("$si") && !is_ip_rfc1918("$du")) { # call is external to external } else if (!is_ip_rfc1918("$si") && is_ip_rfc1918("$du")) { # call is external to internal } } Hope that makes sense and help you a little. Regards, David Villasmil email: david.villasmil.work@gmail.com<mailto:david.villasmil.work@gmail.com> phone: +34669448337 On Thu, Nov 21, 2019 at 6:11 AM Patrick Wakano <pwakano@gmail.com<mailto:pwakano@gmail.com>> wrote: Hello list, Hope you are all doing well! I am trying to figure out a way to retrieve the local socket the t_relay() has decided to use in a mhomed=1 env. Is there a way to do that? I couldn't find any variable other than the $snd ones that maybe have this info, but I am not using onsend_route anyway..... I am after this value because this is what I can use to figure out if I need to engage RTPEngine with parameters "external, internal", "external, external", "internal, external" or "internal, internal". In my case, my server is in between two networks, and calls can traverse or can be routed back to the same interface depending on what was decide by the LCR module. Signalling is fine, but engaging the RTPEngine must be done with the correct parameters to get the correct IPs in the SDP, other else I get one way audio in the call..... Any help is much appreciated! Thank you! Kind regards, Patrick Wakano _______________________________________________ Kamailio (SER) - Users Mailing List sr-users@lists.kamailio.org<mailto:sr-users@lists.kamailio.org> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

Thanks for the replies and examples! Much appreciated! I was thinking of something similar to David suggestion, but I think this is not 100% reliable. It may fail in cases where my kernel routing table has some rule where a private IP is reachable via my external interface but different GW for example (multiple IPs in the same interface or more complex network architecture with VPN or direct link with some endpoint).... So given Kamailio already consults the kernel looking for the correct interface to a given destination, I thought this is actually the correct information I should use in my script. The only problem is that apparently Kamailio is not exposing this info for the script writer.... Karsten suggestion should probably work but in short this is just a way to statically save in DB the network routing information I know before hand. If this route changes (which should not happen often I agree) then I have to update the DB. And also this DB data could be replaced by some logic in my script if I had access to the chosen socket... That's exactly the purpose of having mhomed=1 in the script, I don't need to save socket info for all my GWs in DB because I am letting Kamailio automatically decide it. And it does pretty well! The only problem now is that I don't know what this decision was and I need it to implement the RTPEngine logic in my script based on the interface the INVITE will go out. Happy to hear more ideas! Thanks, Kind regards, Patrick Wakano On Thu, 21 Nov 2019 at 20:07, Karsten Horsmann &lt;khorsmann(a)gmail.com&gt; wrote:

Yes David, we have all sorts of weird things (specially legacy installations where creativity really shined....). Also, in some private network architectures my external interface may not have a public IP at all.... Anyway, I first thought about applying some logic on the destination IP, but it is only reliable if I know my routing table, and this task Kamailio already performs when relaying.... The easiest way for now seems to save the info in the DB, so I explicit tell from which socket each GW is reachable.... And for curiosity I attempted the $snd() variables but they don't have the socket information.... the $snd(ip) has the destination IP, not my local socket as the doc may suggest.....The $branch variable ( http://www.kamailio.org/wiki/cookbooks/5.2.x/pseudovariables#branch_name_-_…) was promising but I couldn't figure out when it is set. In my branch_routes it is always null...... On Fri, 22 Nov 2019 at 09:15, David Villasmil < david.villasmil.work(a)gmail.com&gt; wrote: