[SR-Users] Nathelper module, FLT_NATS, FLT_NATB

[SamyGo]

This is a great thread, really full of answers and concepts for me atleast.
:)

On Mon, Jun 25, 2012 at 5:57 PM, Richard Brady <rnbrady at gmail.com> wrote:

> Klaus / Daniel
>
> Thanks again for assistance with this.
>
> I've tried the solution based on add_contact_alias() and
> handle_ruri_alias() and it works perfectly.
>
> Richard
>
> On 22 June 2012 13:47, Klaus Darilion <klaus.mailinglists at pernau.at>
> wrote:
> >
> >
> > On 22.06.2012 13:50, Richard Brady wrote:
> >>
> >> Thanks guys, fantastic answers.
> >>
> >> You mention that NAT detection happens before save() and the flag is set
> >> by lookup() which makes much more sense. However, if Kamailio is not the
> >> registrar, as is the case with my current project, those functions are
> >> not called, so an alternative is needed. There are clearly several
> >> options.
> >>
> >> The solution I have gone for is to replace fix_nated_register() with
> >> fix_nated_contact() so that the REGISTER request is relayed with a
> >> modified Contact header containing the external ip:port of the client.
> >
> >
> > The cleanest solution would be to use add_contact_alias() and
> > handle_ruri_alias(). The do not change the contact but put the public
> > address into a uri parameter. Thus, the URI seen by the client is always
> the
> > one it sends:
> >
> http://www.kamailio.org/docs/modules/3.2.x/modules_k/nathelper.html#id2550431
> >
> >
> >> That is then stored by the registrar (FreeSWITCH in my case) and used
> >> later to originate calls for that user. The FreeSWITCH know to send
> >> those calls to Kamailio through either use of the Path header and module
> >> in Kamailio, or through static configuration of fs_path or proxy
> >> parameters in FreeSWITCH.
> >
> >
> > This is fine.
> >
> >
> >> The works for the first INVITE to the registered client behind NAT. But
> >> that client sends back a 200 OK with a Contact header containing its
> >> private IP address, and so fix_nated_contact() needs to be invoked on
> >> that response, and normally it would be due to FLB_NATB being set, but
> >> if Kamailio was not the registrar then that flag is not set. So I need
> >> to detect NAT on the client at the time of receiving the reply, or
> >> alternatively by having the registrar store a cookie and setting it
> >> based on that.
> >
> >
> > You are correct. For in-dialog messages received from SIP clients I would
> > always use add_contact_alias() and remove the NAT flags completely.
> >
> >>
> >> I suppose then my next question then is can I call nat_uac_test() on a
> >> UAS?
> >
> >
> > Today, almost any SIP clients are SIP symmetric. This means, that they
> > receive SIP from the some port/connection where they send. Thus, skip the
> > NAT tests completely and always use add_contact_alias() for messages
> receive
> > from SIP clients and handle_ruri_alias() for messages sent to SIP
> clients.
> >
> > Depending on if you use Freeswitch also as media relay you can also
> remove
> > the media proxy stuff from the Kamailio config.
> >
> > On important thing is NAT-keep-alive. This is usually done by nathelper
> > module by querying the location table for contact with NAT-flag set.
> Thus,
> > either you do NAT keep-alive by freeswitch (e.g sending OPTIONS
> requests) or
> > do it in your Kamailio proxy (e.g. set the nat_bflag
> >
> http://www.kamailio.org/docs/modules/3.2.x/modules_k/usrloc.html#id2541477
> > and call save("location","0x02") before relaying REGISTER to freeswitch.
> > Then Kamailio will do NAT-pinging. Note, if you want to keep-alive only
> for
> > successfully registered clients, you man want to call save() in the
> > reply-route of the REGISTER request).
> >
> > regards
> > Klaus
>
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