Re: nscd and DNS cache

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On 05/16/2012 10:11 AM, JD wrote:
> I have nscd running.
> /etc/resolv.conf starts out with
> nameserver 127.0.0.1
> nameserver 192.168.1.254
>
>
> The 192.168.1.254 is the router, which has been a fast and reliable resolver.
>
> So, to test nscd caching behavior,
> I browse (using FF) over to any website.
> After some time, the address is resolved and the page comes up.
> I kill the tab of the page, and open a new tab and aim the browser
> at same url. Browser again says: looking up whatever....com and takes
> several seconds to resolve it.
>
> I thought that nscd is supposed to cache the translation from the
> first lookup.
>
> Am I to believe that the browser is NOT using /etc/resolv.conf?
> If not, what is it using?
> Or could it be that nscd is useless in this respect?
>

I've not looked at nscd in a long time....but I never could see the value in it and
never could get it to what I thought was a working or useful configuration for my needs.

No browser or application uses resolv.conf directly.  They make calls to the resolver
libraries which in turn use it.

IMO, if your router does caching name services there really is no benefit to having
systems do their own caching since the overhead of local requests should be small. 
However, it seems that your router may not be caching since it is taking several seconds.

In cases where the router isn't doing caching, or is doing it poorly, I prefer to
simply run bind on a single server and point all the systems to it for resolution.

With the current Fedora systems this is easy.  All one need to do is install bind and
bind-chroot and enable/start the service.  On the "bind" host all you need is
127.0.0.1 defined as a nameserver.  Then, if you use a tool such as "wireshark" you
will see that requests will only go out if the answer is not in the cache or the TTL
has expired.

-- 
Never be afraid to laugh at yourself, after all, you could be missing out on the joke
of the century. -- Dame Edna Everage
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