[Serusers] When is a DNS lookup performed?

Maxim Sobolev sobomax at portaone.com
Thu Jun 26 22:26:04 CEST 2003

Andrei Pelinescu-Onciul wrote:
> 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.

Not quite. Run-time reverse DNS lookups also performed when you are 
doing comparisons involving src_ip.


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