nscd and DNS cache

[fedora]

... or try dnsmasq

suomi

On 05/16/2012 08:54 AM, JD wrote:
> On Tue, May 15, 2012 at 9:20 PM, Ed Greshko<Ed.Greshko at greshko.com>  wrote:
>> 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.
>>
> I understand the libs are what make calls to the resolver. But even
> the resolver must look
> at /etc/resolv.conf. If it is empty, NOTHING gets resolved.
> I was using nscd thinking it is a lightweight caching resolver. But as
> it turns out it is useless.
> Time for fedora to bury it :)
> Re: My router: it does very little if any caching - and has no
> configuration for it at all.
>
> I will try bind.
>
> Thanx Ed.
>
> JD