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Old January 2nd 18, 03:00 AM posted to alt.windows7.general,microsoft.public.windowsxp.general
Brian Gregory[_2_]
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Posts: 166
Default Windows DNS cache

On 01/01/2018 03:45, Mayayana wrote:
"Brian Gregory" wrote

| I was wondering what all this talk was of Windows
| DNS Cache. I'd never heard of it. It should be clarified
| that "Windows DNS Cache" is actually the DNS Client
| service. It doesn't need to be enabled at all for most
| people. It's possible that people on a network with
| Active Directory may need it. I'm not familiar with
| that. I suspect they don't and that it will only save
| on a few intranet calls.
| I've had DNS Client disabled for years and see no
| reason to enable it.
|
| You don't need it if you LAN has it's own DNS cache but I guess it might
| be worth saving the 12MB of RAM it uses to save doing unnecessary DNS
| lookups over the Internet.
|
?? This post was close to 2 years old.

I don't have a LAN. I don't allow sharing with other
computers for security reasons.


Surely your PC isn't connected directly to the internet?
You should have a firewall or NAT and firewall in between.
If you have NAT then you LAN is the connection between the NAT box and
your PC. I guess if you only have a firewall then it's reasonable to say
there is no LAN.


If you look it up I think you'll find that the "time to live"
for these things is very brief, anyway. A day or less:

http://webcache.googleusercontent.co...&gbv=1&ct=clnk

Browsers can store their own cache. The default DNS
cache expiry in Firefox is 1 minute. The idea is not to
store a phone book but rather to save repeated DNS
requests for the same URL during a session.


Maybe, but if a DNS result says it's valid for longer why not cache it
for a bit longer.

It's rather a pathetic PC by modern standards that can't spare 12MB of RAM.

Mind you I'm not sure that the DNS cache in Windows 7 does cache for
that much longer than a minute.


If the cache were long-lived there would be problems
when a site changes IP address. I ran into that at one
point when I found that several sites had disappeared.
I finally figured out that the DNS proxy I use, Acrylic,
stores a much longer DNS stash. Something like 10 days.


It was probably broken then. Anything that caches DNS results should be
asking for the Time To Live of results of queries it caches and not
keeping them any longer than that as an absolute maximum. If that's too
complicated just keep them, say, an hour.


Most of the time that's OK, but only if you know about
it and know to clear that cache if anything goes wrong.


It's probably a broken cache if it keeps results longer than a day or
two absolute max. I think many people would set a DNS cache to cache no
longer than a day or two no matter what TTL was reported. Just in case
the TTL was over optimistic.


Aside from that, I don't know of any reason to cache
DNS or to worry about cache. The storage time is brief
and the time required for a DNS query is negligible. So
it doesn't much matter one way or the other.


All those queries to separate site for pictures, javascript, google
APIs, Google adverts, other adverts etc. etc.

--

Brian Gregory (in England).
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