Re: Kamailio as a Stateless Smart SIP Proxy

Hi,

Yes, that's exactly what those functions enable. 

When you receive the REGISTER request, you use set_contact_alias() / add_contact_alias() to add an `;alias` parameter to the Contact, which reflects the client's external IP/port/transport. You then pass that REGISTER request onto the registrar.

When you get an incoming request from the registrar to the client, you use handle_ruri_alias() to read the `;alias` parameter and load the IP/port/transport values into the destination set ($du), while stripping the `;alias` parameter off the RURI. You then t_relay() the request, which will follow $du to the next hop read from the `;alias` parameter.

-- Alex

> On Jul 11, 2025, at 4:28 PM, Antonio <[email protected]> wrote:
> 
> Thanks for the reply
> 
> I want to use Kamailio as a proxy, but a smart one. 
> It doesn't store anything, but: 
> • Modifies REGISTER requests → adds the client's IP/port to Contact 
> • So when the PBX sends an INVITE back, Kamailio reads this data from the R-URI and forwards the call to the client
> 
> Hope it makes sense.
> 
> 
> On Fri, Jul 11, 2025 at 10:14 PM Alex Balashov via sr-users <[email protected]> wrote:
> Hi,
> 
> The set_contact_alias() / handle_ruri_alias() functions from the `nathelper` module[1] are quite ready-made for this use-case, though you may need a more sophisticated approach if the upstream registrar does not support Path[2][3].
> 
> -- Alex
> 
> [1] https://kamailio.org/docs/modules/6.0.x/modules/nathelper.html
> 
> [2] https://datatracker.ietf.org/doc/html/rfc3327
> 
> [3] https://kamailio.org/docs/modules/6.0.x/modules/path.html#path.f.add_path
> 
> > On Jul 11, 2025, at 6:19 AM, Antonio via sr-users <[email protected]> wrote:
> > 
> > Hi everyone,
> > Do we have a ready-to-use Kamailio role or configuration for:
> > 
> > “Kamailio as a Stateless Smart SIP Proxy”,
> > Specifically one that uses Contact Header Encoding?
> > 
> > That is — a proxy where Kamailio does not store registration state,
> > but encodes the client’s IP and port into the Contact header during REGISTER,
> > and later decodes it from the INVITE to forward the call back to the client.
> > Thanks in advance!
> > -- 
> > 
> > Antony
> > [email protected]
> > __________________________________________________________
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> 
> --
> Alex Balashov
> Principal Consultant
> Evariste Systems LLC
> Web: https://evaristesys.com, https://www.csrpswitch.com
> Tel: +1-706-510-6800
> 
> __________________________________________________________
> Kamailio - Users Mailing List - Non Commercial Discussions -- [email protected]
> To unsubscribe send an email to [email protected]
> Important: keep the mailing list in the recipients, do not reply only to the sender!
> 
> 
> -- 
> 
> Antony
> [email protected]

--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com, https://www.csrpswitch.com
Tel: +1-706-510-6800

__________________________________________________________
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