Kamailio behind NAT - Wrong VIA Header - sr-users

3 Nov 2014


      Hello,
We are using Kamailio 4.2 and RTPEngine 3.3  hosted on a VM behind NAT in
Google Cloud Engine.
Asterisk 11 + Kamailio + RTPEngine are on the same machine and Kamailio is
used as WebRTC Gateway.
INVITES, that are rewritten by Kamailio look like the following:
INVITE sip:eTden7KoNSdMVCUNYIwmz@wh2.24dial.com SIP/2.0
Record-Route: sip:0.0.0.0:5064;lr=on;nat=yes
Via: SIP/2.0/UDP 0.0.0.0:5064
;branch=z9hG4bK86f5.88fb7f8810c91758b5f3962420d3a4ef.0
Via: SIP/2.0/UDP 10.240.1.95:5060
;received=127.0.0.1;branch=z9hG4bK05952ee6;rport=5060
Max-Forwards: 69
From: "Anonymous" sip:anonymous@anonymous.invalid;tag=as7900b63f
To: sip:eTden7KoNSdMVCUNYIwmz@wh2.24dial.com
Contact: sip:anonymous@10.240.1.95:5060;alias=127.0.0.1~5060~1
Call-ID: 0662d336694c60ed60ed5310571a1aee@10.240.1.95:5060
CSeq: 102 INVITE
User-Agent: Asterisk PBX 11.13.1
Date: Mon, 03 Nov 2014 09:01:39 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO,
PUBLISH, MESSAGE
Supported: replaces, timer
Content-Type: application/sdp
Content-Length: 676
P-hint: outbound
As you can see, Kamailio uses 0.0.0.0 for Record-Route as well as for VIA
Header.
It uses the address configured in kamilio.cfg (listen=udp:0.0.0.0:5064)
I know, that we could use the advertise parameter to tell kamailio the
external IP. The problem is, that IPs in GCE are dynamically assigned to
the VMs. Thus static configuration of external IP is not sufficient for our
setup.
Is there a way, to let Kamailio gather it's external IP dynamically. (E.g.
using a STUN server or something like that?)
Another possibility would be to tell Kamailio it's external IP via a start
parameter. Is that possible?
Any help would be grateful.
Kind regards,
Marko Seidenglanz