[Dnsmasq-discuss] Time to live for cache

Simon Kelley simon@thekelleys.org.uk
Sun, 06 Feb 2005 22:03:07 +0000


Anand Rangarajan wrote:
> I'm really sorry if this question has already been answered in the 
> documentation. I couldn't find it. I have dnsmasq running on my linux 
> box so that I can cache DNS requests because for some reason my ISP 
> nameserver takes a long time to respond. For example, if I type 
> harrypotter.com, I get  a "Looking for harrypotter.com" for about 5 
> seconds which is then followed by name resolution. When I run dnsmasq, 
> it caches harrypotter.com (I know this because I've turned on logging 
> and I see it in the messages) but it doesn't seem to cache it for very 
> long. I can't be sure how long the cache survives, but after half an 
> hour, it still takes 5 seconds to resolve the same request made earlier.
> 
> Q: How do I make the cache live longer---say a month?

The time which an individual name lives in the cache is controlled by 
the owner of the domain - Answers to DNS queries comes with a 
"Time-to-live" which is the number of seconds for which it is safe to 
cache the information. That value is set by the authoritative servers 
for the domain - it varies from seconds to weeks.

If you use a tool like "dig" to do queries, you can see the TTL values 
in the answers.

> 
> I've switched off ipv6 since firefox and ipv6 don't work well together 
> on my SuSE 9.2 box. Also, the same behavior is noticed for some other 
> requests like latimes.com, consc.net. Oddly enough, name resolution in 
> firefox on XP Pro on the same box is very fast---one second or less. 
> Very sad. This is why I looked into dnsmasq in the first place.

This is worth chasing: it implies that there might be a DNS 
misconfiguration in the Linux install. - If it's using the same servers 
as XP, and trying them in the same order, then it should be as fast.


HTH


Simon.

> 
> Thanks for any help.
> 
> Anand
> 
> 
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