[Serusers] Rewriting URI in the Contact field
Jiri Kuthan
jiri at iptel.org
Tue Jan 14 09:46:00 CET 2003
Few more notes on this construct:
a it takes two servers in series; the first one in chain makes the
NAT fixing job, the other one acts as proxy/registrar; the reason is
the NAT changes to a request are only used to generate outoging request
and do not affect registrar; thus, you first need to send the updated
request out; one could still have only one server running (be it easier
or not) with a routing policy, which makes the request pass the same
server in two rounds -- first one de-natifying, the second real one
b it takes generating symmetric replies and accepting rport in relayed
replies -- I think that is a reasonable thing to add to ser core
c the routing policy needs to be set up in such a way, the de-natifying
instance of SER is always in the path -- otherwise subsequent inbound
requests would be routed based-on Contact directly to NAT, would not
use symmetric path opened by initial REGISTERs and fail;
the denatifier thus needs to use record-routing
d for the same reason, all initial inbound requests to natted users proxied
by the main server need to be statically routed to the de-natifier
-Jiri
the examples bellow demonstrate in ascii charts some more details;
A:B is address:port of natted phone, X:Y the natted A:B, C:D that of
denatifier
network setting:
fone F: A:B NAT N: X:Y proxy D proxy P
~
/------\ ~ /-------------\ /--------------\
|phone | -------->~----------->|denattifying |--------------->|registrar/ |
\------/ ~ |ser/outbound | |inbound proxy |
~ |proxy | \--------------/
\-------------/\ ^
\ /
\----> outbound /
domains
1) registers go from F, are rewritten by D and processed at P
2) INVITEs from F visit D, Contact is rewritten, rport is introduced,
request is record-routed, so that other party's request visit D too;
3) INVITEs from outside visit first P, contacts rewritten previously
by D are put in r-uri, requests are forwarded statically to D,
and D forwardes by uri to the fone F
At 06:27 PM 1/10/2003, Maxim Sobolev wrote:
>On Fri, Jan 10, 2003 at 03:37:46PM +0200, Maxim Sobolev wrote:
>> Sounds reasonably - I'll do it that way.
>
>I am planning add a new nathelper module, which will export the
>following functions:
>
>add_rport() - insert a rport= parameter into the first Via field
>fix_nated_contact() - replaces host:port in Contact field with host:port
>we received this message from
>add_direction_passive() - adds direction=passive option to the SDP
>
>Then it would be possible to do the following at the very top of config
>before any other REGISTER/INVITE processing:
>
>if (method == "INVITE" || method == "REGISTER") {
> if (search("User-Agent: Cisco ATA.*") {
> add_rport();
> if (method == "INVITE") {
> add_direction_passive();
> };
> if (method == "REGISTER") {
> fix_nated_contact();
> };
> };
>};
>
>Does it sound reasonably for you?
>
>-Maxim
>
>>
>> Thanks!
>>
>> -Maxim
>>
>> On Fri, Jan 10, 2003 at 02:15:11PM +0100, Jan Janak wrote:
>> > On 10-01 14:32, Maxim Sobolev wrote:
>> > > Folks,
>> > >
>> > > I need an advise on how to better implement one feature, which isn't
>> > > currently present in SER. We need to allow UAs behind NAT properly
>> > > register with the registrar - by "properly" I mean that host:port portion
>> > > of URI in Contact field should not be used, but host:port the request
>> > > came from should be used instead. By definition we know that those UAs
>> > > will support symmetric SIP signalling, so that this scheme will work just
>> > > fine.
>> > >
>> > > In my opinion there are two ways to do it: either add new rewritecontact*
>> > > family of functions similar to rewritehost ones. or add a new flag for
>> > > the save() function. This is where I need your help - which implementation
>> > > looks better for you (or maybe you have even some better idea), since
>> > > we are really interested in inclusion of our changes into the mainline to
>> > > reduce our local hacks.
>> > >
>> >
>> > This should be implemented as a standalone module for ser. I want to keep
>> > registrar clean, it should not be aware of NATs. So, create a new module
>> > for ser that will contain all the NAT traversal helper functions, the
>> > functions will be then called from the config script.
>> >
>> > That includes modifications of contact, adding rport to Via and so on.
>> >
>> > regards, Jan.
>> >
>>
>>
>> _______________________________________________
>> Serusers mailing list
>> serusers at lists.iptel.org
>> http://lists.iptel.org/mailman/listinfo/serusers
>_______________________________________________
>Serusers mailing list
>serusers at lists.iptel.org
>http://lists.iptel.org/mailman/listinfo/serusers
--
Jiri Kuthan http://iptel.org/~jiri/
More information about the sr-users
mailing list