I need a DNS failover solution.

Posted on 2009-04-21
Last Modified: 2013-12-24
I need to failover from one IP address to another is a server goes down. I have found some services and come software applications that claim they can failover the IP addresses in under 5 minutes.

Does anyone have any experience with either the software DNS failover packages or the failover DNS services?
Question by:jimmylew52
    LVL 70

    Accepted Solution


    They tend to be pretty okay. They utilise network monitoring stations running from geographically split locations.

    There are limitations. It only works if the system querying yours honours the Time to Live (TTL) set on the record. Most will, but a few won't. I suspect you'll find AOL won't.

    DNS failover will always be on the low end of the price range because of it's reliance on a system that is difficult to fully control (you only control the authoritative servers).

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    Author Comment

    Do you know the reasonable lag time between server fail and the DNS propagating  thru out the internet with these companies? They claim under 5 minutes. We do not deal with AOL. I understand it should vary but I am looking for what I can reasonably expect. The 48 to 72 hours Yahoo promises is too long. I need something in the 2 - 6 hour range.
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    Expert Comment

    by:Chris Dent

    They really do mean 5 minutes.

    Propagation of record changes is based on the TTL, if the TTL is short (as with these failover solutions) then propagation should also be short.

    The frequently quoted 24 - 72 hour change over is based on a longer TTL, as longer is considered to be better for the world (less load on DNS servers around the world).

    In many cases TTLs range from 1 to 3 days, this is true of NS records on TLD (Top Level Domain, com, net, etc, etc) servers. Those are the DNS server addresses you give your Registrar for your domain. However, that doesn't come into play because there's no need for those to change.

    The only time that won't be the case are when you deal with a system that uses additional caching (and some proxying) which prevents them from seeing the change, despite the low TTL. I don't hear about a large number of those, if it were MX records then a few of the big web-mail providers would be a consideration.

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    Author Closing Comment

    Thanks, I appreciate the quick response and the information.

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