[SR-Users] How to detect NAT during authenticated registration of clients which adjust the headers

David Villasmil david.villasmil.work at gmail.com
Fri Feb 28 14:57:08 CET 2020


There probably is a better way of doing this, but maybe you can store the
fact that the first register came from a natted device in the locations
table (or a hash).

Or maybe add a parameter when challenging where you state the client is
natting?

Something like this

https://kamailio.org/docs/modules/3.1.x/modules_k/siputils.html#id2769802


Hope that helps

David

On Fri, 28 Feb 2020 at 12:03, Awal Junanto <a.junanto at gmail.com> wrote:

> Hi,
>
> We are building a service where we need to detect NAT when the clients
> register to our server. We are struggling in analyzing NAT status of some
> clients which modify their IP addresses/ports in the headers according to
> the value of "received" parameter sent during "401 Unauthorized" response.
>
> Here's the flow:
>
> Client->Server
> REGISTER sip:...
> Via: SIP/2.0/TLS 192.168.0.1:41157
> ;rport;branch=z9hG4bKPj30093e5d-550d-4d4c-a9a2-22c3bd1cda7e;alias
> Contact: <sip:user at 192.168.0.1:42251;transport=TLS;ob>
> ...
> Server->Client
> SIP/2.0 401 Unauthorized
> Via: SIP/2.0/TLS 192.168.0.1:41157
> ;rport;branch=z9hG4bKPj30093e5d-550d-4d4c-a9a2-22c3bd1cda7e;alias;received=1.2.3.4
> WWW-Authenticate: ...
> ...
>
> Client->Server
> REGISTER sip:...
> Via: SIP/2.0/TLS 1.2.3.4:6201
> ;rport;branch=z9hG4bKPj30093e5d-550d-4d4c-a9a2-22c3bd1cda7e;alias
> Contact: <sip:user@ 1.2.3.4:6201;transport=TLS;ob>
> Authorization: ...
> ...
>
> By the time the client is authenticated, there is no way to detect whether
> the request was coming from a natted device or not by just analysing the
> Via or Contact headers.
>
> Thanks in advance.
>
>
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-- 
Regards,

David Villasmil
email: david.villasmil.work at gmail.com
phone: +34669448337
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