[SR-Users] Using Kamalio as a proxy for internal servers

[Sergey Safarov]

To resolve such an issue I switched to use IPv6 on internal SIP servers for
signaling and IPv4 for RTPmedia.

For me works like a charm.

On Mon, Sep 7, 2020 at 9:58 AM Olle E. Johansson <oej at edvina.net> wrote:

> You need to define another listen= without the advertise for communication
> with internal servers. Either another IP or another port.
>
> /O
>
> On 6 Sep 2020, at 17:34, Moshe Katz <kohenkatz at gmail.com> wrote:
>
> Hello all,
>
> (Note: I previously posted a more detailed version of this question on
> StackOverflow at https://stackoverflow.com/q/63760506/829970 . This
> version is simplified to fit better in an email.)
>
> I have Kamailio 5.4.1 (and RTPEngine) running on an internal server with a
> private IP address 172.31.7.96 and One-to-one NAT to an external IP
> address. The external IP is 192.0.2.100. (Note: The internal IP addresses
> are all unedited, but the public IPs have been replaced with TEST-NET-1 and
> TEST-NET-2 example addresses.) I will eventually be doing transcoding with
> RTPEngine, but for now this is a simple SIP Proxy.
>
> Kamailio is installed on Ubuntu 18.04 using the DEB packages from
> dev.kamailio.org/kamailio54 and is using the stock configuration that
> comes with those packages, except for the following changes:
>
> #!define WITH_NAT
> #!define WITH_RTPENGINE
> #!define WITH_MYSQL
> #!define WITH_AUTH
> #!define WITH_IPAUTH
>
> listen=udp:0.0.0.0:5060 advertise 192.0.2.100:5060
>
> #!define DBURL "mysql://kamailio:REAL_PASSWORD_HERE@127.0.0.1/kamailio"
>
>
> I have internal SIP servers with private IP addresses in the 172.31.7.0/24
> range that I want to have send all SIP traffic through the Kamailio server.
> The internal servers are running a Java SIP client with the
> `OUTBOUND_PROXY` setting set to 172.31.7.96.
>
> The problem I have is that the SIP `200 OK` message sent by Kamailio to my
> SIP server has its `Record-Route` header set to the public IP address
> `192.0.2.100` instead of the private address `172.31.7.96`. The SIP client
> therefore tries to send the `ACK` message back to the public address, but
> it has no route to the public address so the ACK never gets sent.
>
> How can I configure Kamailio to use the public IP for external traffic but
> the private IP for communicating with internal machines on the same subnet?
>
> I tried setting `mhomed=1`, but the machine isn't actually multi-homed so
> that didn't work.
>
> I thought of adding a second listen line `listen=udp:172.31.7.96:5061`
> and having the internal servers talk to port 5061, but that doesn't work
> because Kamailio uses the 5061 definition for the external side too.
>
> I see in the docs that it is possible to name the listener lines, but I
> don't understand how to use those names in a way that would be relevant to
> my issue.
>
> Thank you very much for your help,
>
> Moshe
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