dynmamic DNS failover

[Barry Margolin]

In article <93nfd8$frf at pub3.rc.vix.com>,
Evgeni Dobrev  <edobrev at eccag.de> wrote:
>
>Hello,
>
>I am trying to do something which I never tried before.
>
>I wan to establish a backup machine which is offsite.  The backupp machine 
>is running a watchdog process which checks whether the HTTP server we host 
>is available. if it is not it updates the DNS servers for the domain and a 
>new A record is created for the HTTP server. and all http requests go to an 
>alternative machine.
>
>My question is : How can I bring the down time to minimum? when I update 
>the DNS it will take some time for the changes to propagate. I have set the 
>TTL in our zone files to 3 mins but I am not sure whether this is all the 
>downtime I will get?

You also need to ensure that the change propagates quickly to the secondary
nameservers.  If both the primary and secondary are running BIND 8 or
higher, the primary will use the NOTIFY mechanism to alert the secondaries
that the domain has changed, and they should transfer the zone almost
immediately.  If they don't all support NOTIFY, you should reduce the
Refresh time to a minimum value.  However, BIND only checks for zones
needing to be refreshed every 15 minutes, so this mechanism can't be used
to make the change propagate faster than that.

>Are there better solution to what I want to do?

There are non-BIND solutions, such as Cisco Distributed Director.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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