disable cashing

[yossi]

Kevin Darcy <kcd at daimlerchrysler.com> wrote in message news:<bo96u3$2i8d$1 at sf1.isc.org>...
> yossi wrote:
> 
> >phn at icke-reklam.ipsec.nu wrote in message news:<bo6j2e$2hfe$1 at sf1.isc.org>...
> >  
> >
> >>yossi <yossi.zadah at audiocodes.com> wrote:
> >>    
> >>
> >>>How I can configure the dns, to disable cashing?  
> >>>thanks
> >>>      
> >>>
> >>You can't. It's a built in part of the design.
> >>    
> >>
> >
> >How can an application actively query the name server in order to
> >detect the possible change, regardless of the Time To Live (TTL)
> >associated with the DNS record?
> >
> If "the name server" is the master for the zone, then it's a moot point, 
> since it's already giving the most up-to-date information available.
> 
> If "the name server" is a slave server, then, short of going out of band 
> and forcing the slave to refresh, your application is at the mercy of 
> replication delays.
> 
> If "the name server" is a non-authoritative (caching) server,then, 
> again, short of going out of band and forcing the server to purge the 
> old cache entry, there's no way to make it fetch the new data.
> 
> Of course, if your application is smart enough, it can try to find the 
> master server itself. But the master server might be "hidden", i.e. it 
> might be behind a firewall and not even on the same network as wherever 
> your app lives. So there are no guarantees here.
> 
>                                                                          
>                                     - Kevin
> 
> 
>                                                                          
>                                        - Kevin

Thank you all for the detailed answer. 
To be more specific, 

my OS is:

# uname -a
SunOS client65 5.8 Generic_108528-07 sun4u sparc
SUNW,UltraSPARCengine_CP-60

In order to activate DNS I made two modifications as follows: 
In the file resolv.conf:
nameserver 192.168.101.6 (DNS server IP)

and in the file : 
# /etc/nsswitch.files:
hosts:      files dns	## <--- Change here

My understanding in DNS is very limited; I assume that I am working in
a "slave server mode".
In my application I am working with ' gethostbyname', it is very
convenient since then I don't have to take care of TTL. The only
problem is where I need to make a query regardless the TTL, calling 
'gethostbyname'  will return the answer (from the cash) since the last
query, which have been initiated as a result of TTL epoch (no new
query).

I can use the res_nquery to force query whenever it is needed, but
then I will need to take care of the TTL.

I thought that it is a good idea to combine these two commands, the
problem with that is: res_nquery doesn't refresh the 'gethostbyname'
tables.

How I can to make the slave to refresh?
How I can force the DNS to issue a query whenever I calling
gethostbyname'?

Thanks again
Yossi