ISP Switch / DNS problem

Barry Margolin barmar at genuity.net
Wed Apr 10 20:48:09 UTC 2002


In article <a926hm$9sv at pub3.rc.vix.com>,  <mrm00k at yahoo.com> wrote:
>
>Mark_Andrews at isc.org wrote in message news:<a8vomi$2jh at pub3.rc.vix.com>...
>> 	In fact you can have the secondaries configured to pull
>> 	from both the old and new addresses.  That way when you
>> 	change addresses the secondary will be not need to be updated
>> 	immediately.
>
>Could I have my ISP set up to pull from the new address if it does not
>exist yet ? Then when the server IP is changed, the secondary DNS
>server will find the new server and pull information from there ?

Yes.  That's what he was suggesting: have the ISP configured to pull from
*both* addresses.  While the old address works, they'll pull from there,
and when you switch to the new address they'll immediately start pulling
from there.  When you list multiple masters, named tries all of them.

>> 	You can also add the new addresses for the critical servers
>> 	a short time (< 30 min) before the change over.  They will
>> 	appear to be multihomed with one interface down.  Once you
>> 	have completed the move you can delete the old address.
>
>I'm not clear on this point. If I add new A records for the new
>addresses of the critical servers then I have 2 A records with the
>same name and different IP addresses. One IP that is online and one
>that is not. Will the resolution process look at both records to see
>which one is correct ?

It's up to the application implementor whether they use just the first
address or try them all.  Most mailers should try them both.  Some browsers
may do failover as well.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.


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