[Serusers] When is a DNS lookup performed?

Andrei Pelinescu-Onciul pelinescu-onciul at fokus.fraunhofer.de
Thu Jun 26 20:03:59 CEST 2003

On Jun 26, 2003 at 12:22, Jamin W. Collins <jcollins at asgardsrealm.net> wrote:
> When does SER perform DNS lookups?  Is it a matter of how the entry is
> made in the ser.cfg?  I ask because one of our customers changed their
> DNS servers and the SER proxy was not updated.  In the ser.cfg all
> routing is done by IP (or I had thought it was).  However, the site
> started experiencing some very odd call drops and after updating the
> resolv.conf on the proxy server with the proper DNS servers (one of them
> had changed) everything was fine.

DNS lookups for the addresses in ser.cfg are performed only once, on ser
startup immediately after reading the cfg. file.
> Should IP address entries be quoted or non-quoted?
It doesn't matter (they have to be quoted for modules functions, like
t_relay_to, they can be unquoted for forward*(...) ).
>Does the presence of
> the quotes cause a DNS lookup even though the item in them is purely
> numeric (i.e. "").
No. Internal ser resolve functions will be called, but in the default
compilation (with -DDNS_IP_HACK added) they will recognize ipv4 & ipv6
addresses and no dns lookup will be performed.

Runtime DNS lookups for requests are performed only for forward (uri:host),
t_relay() and other uri involving forwarding functions.


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