Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!BRL.MIL!tcs
From: tcs@BRL.MIL (Terry Slattery, SECAD)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  Domain resolver resets needed
Message-ID: <8903231027.aa08575@SEM.BRL.MIL>
Date: 23 Mar 89 15:27:34 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 26

> This points out the need for some mechanism to update domain resolver
> caches before their expiration so that when address changes occur they
> do not result in loss of connectivity.

The current refresh entry should satisfy this need if the changes are
expected in advance.  A week before the change, set the refresh
interval to 24 hours.  Hosts will begin using the 24 hour interval
when their current info expires.  One day before the change, set the
refresh interval to something smaller, perhaps 2 or 4 hours.  When the
change is made, hosts will only be using the wrong addresses for at
most 2-4 hours.  When things are stable, change back to your normal
refresh interval.

For this to work, you must know at least your current refresh interval
in advance of the change date.  There will also be a slight increase
in network traffic as hosts refresh more frequently.  Without
significantly more state in the nameserver about who requested host
info, there is no easy way to flush remote caches.  You already know
the alternative - answer phone calls from remote sites who can't
contact you and have them do a manual flush.

I noticed that wsmr-simtel20.army.mil has a ttl of 24 hours, not one
week.  All DNS hosts should work properly after this time and only
hosts using a static host table should have problems.

	-tcs