Win2k caches ip addr. after name resolution from dns?

Pete Ehlke pde at ehlke.net
Tue Sep 25 06:21:00 UTC 2001


* Danny Mayer <mayer at gis.net> said, on [010924 20:03]:
> 
> At 09:23 PM 9/24/01, Sanjivendra Nath wrote:
> 
> >Is there anyway for us to force the MS clients (namely, IE 5.0) to go to the
> >DNS for name resolution always, or at least limit the time during which it
> >caches the ip address of a site?
> 
> No.  That's totally under the control of the designer of the client. Why would
> you think otherwise?  Caching can be limited to the extent that the client
> wants to by giving the address a TTL that you desire.
> 
Well, yes and no. IE 5 seems to do a fairly decent job with dns response
caching, but win2k itself, at the OS level, is almost irretrievably
broken in this respect. It implements a local resolver cache, similar to
Sun's nscd, that cannot be turned off and which seems to, at the very
least, have its own ideas about TTL regardless of the value contained in
the RR itself. It also seems to do odd things with TTLs when an A and a
CNAME record that points to it have different TTLs, and it dosne't
behave as one expects with round robin records. When confronted with a
round-robin response, the w2k resolver cache seems to simply pick one
record and ignore the rest. This is the behaviour that the OP is seeing.

There used to be a TechNet article that described how to reduce the
resolver cache's TTL value to one second, effectively kneecapping it. I've
lost the URL, though, and a half hour of searching microsoft.com has
failed to turn it up :/

-Pete


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