DNS Failover

Pete Tenereillo pt_bind at hotmail.com
Thu Oct 14 16:08:09 UTC 2004


A new DNS resolution is required if a single A record is returned. The only 
version of IE that does a new DNS resolution without being restarted is 
WinXP SP2. Microsoft was notified that GSLBs do not work correctly for 
failover with single A records, some of the vendors worked with them, and 
they changed the behavior in the release that came out a few weeks ago. 
WinXP SP1 and previous versions of IE, and NetScape (i.e. the vast majority 
of Internet clients) have the issue. I don't know about Firefox etc. 
Browsers aside, many proxy servers will defeat what you are trying to do 
with failover and your GSLBs.


----- Original Message ----- 
From: "Maria Iano" <maria at iano.org>
To: <comp-protocols-dns-bind at isc.org>
Sent: Thursday, October 14, 2004 7:53 AM
Subject: Re: DNS Failover

> We use GSLBs for load balancing between web sites but mostly for failover 
> in case a primary site goes down. Usually they work pretty well. It's true 
> that some name servers don't handle TTLs properly, but from my experience 
> at watching the traffic I can tell you that it works for the vast 
> majority.
> Personally I haven't found it to be the case, as stated in the article you 
> mention, that I have to restart my browser for the new A record to take 
> effect. It has been my experience that the browser catches on and goes to 
> the new IP pretty much immediately. The browsers I use most frequently are 
> Firefox, Safari and IE. They are recent versions. Maybe the problems you 
> describe occurred with older versions?...
> Maria
>> -----Original Message-----
>> From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org] On
>> Behalf Of Pete Tenereillo
>> Sent: Thursday, October 14, 2004 9:00 AM
>> To: Greg Maccarone; Anthony Wilkins
>> Cc: comp-protocols-dns-bind at isc.org
>> Subject: Re: DNS Failover
>> Anthony mentioned he has a Web app, so that TTL trick won't work
>> reliably.
>> The low TTL would be seen by servers "throughout the rest of the world"
>> but
>> TTL are ignored by most clients (and many proxy servers), so all
>> existing
>> users (and users that share such proxies) will be stuck on the downed
>> server. Check out:
>> http://www.tenereillo.com/GSLBPageOfShame.htm
>> for details. IMO for failover you are better off putting both servers at
>> the
>> same site, using local load balancing (there are some very cost
>> effective
>> solutions available now) and redundant power and Internet connections.
>> Pete.
>> ----- Original Message ----- 
>> From: "Greg Maccarone" <gmaccarone at gmail.com>
>> To: "Anthony Wilkins" <anthony_wlkns at yahoo.com>
>> Cc: <comp-protocols-dns-bind at isc.org>
>> Sent: Tuesday, October 12, 2004 11:46 AM
>> Subject: Re: DNS Failover
>> > On Tue, 12 Oct 2004 11:01:45 +0200, Anthony Wilkins
>> > <anthony_wlkns at yahoo.com> wrote:
>> >> Hi, is there anybody who can help me in finding a solution to a
>> problem
>> >> I have?
>> >>
>> >> My web server is sometime temporarily down and I want people to go to
>> my
>> >> remote site where I have a backup web server. Can I change DNS on the
>> >> Internet fast enough for incoming requests to be handled by my
>> redundant
>> >> web server? Normally I don't want traffic to go to the remote site.
>> >>
>> >> Thanks, Anthony W.
>> >>
>> >>
>> >
>> > A way this could be achieved with DNS is to have a low TTL on the host
>> > entry that could be changing because of the outage.  Then in most
>> > cases it would take no longer than the specified TTL for the changes
>> > to be seen throughout the rest of the world.
>> >
>> > my $.02.
>> >
>> > -- 
>> > Greg Maccarone
>> > gmaccarone at gmail.com
>> >
>> >

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