[sr-dev] dns= and rev_dns= parameter

[Andrei Pelinescu-Onciul]

On Jul 08, 2009 at 10:58, Klaus Darilion <klaus.mailinglists at pernau.at> wrote:
> Thanks!
> 
> Just for clarification:
> 
> >dns
> >
> >This parameter controls if the SIP server will try doing a DNS lookup
> >on the address in the Via header of a received sip request to decide
> >if adding a received=<src_ip> parameter to the Via is necessary. Note
> >that Vias containing DNS names (instead of IPs) should have received=
> >added, so turning dns to yes is not recommended.
> >
> >Default is no.
> 
> Does this mean that, if the Via header in the received message contains 
> a domain and:
> 
> dns=yes, a lookup is done, and if the domain resolves to the src_ip, 
> then the "received" parameter is not added, but only added when the 
> domain resolves to a different IP address?

Yes.
> 
> dns=no: the "received" parameter is always added?

Yes, if the address in Via is a DNS name and not an IP (and this is the
recommended behaviour according to the rfc).

> 
> What about the behavior when the Via header contains an IP address (does 
> this parameter affects the behavior)? Is the "received" parameter always 
> added, or only if it Via-IP differs from source-IP? What about existing 
> "received" parameter - will they be deleted/overwritten.

If the Via contains an IP, received is only added if the Via-IP!=src_IP.

> 
> I ask because some time ago we had problems in Kamailio.

I think they do exactly the same thing in kamailio. These config params.
are very old, from the early days of ser and I doubt anyone touched
them.
BTW: they can be turned on from the command line (-r and -R).

Andrei