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DNS Nameserver, order of usage

Posted on 2011-03-09
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Last Modified: 2013-12-25
I use multiple nameservers for a critical domain. We use 5 nameservers.

If I have 5 nameservers listed with our registrar, is it the case that the 5th nameserver will not be used by any visitors (dns resolvers), unless the first 4 are down or unavailable?

Can I count on this order to remain intact?

Meaning... If the first nameserver (let's call it ns1) is responding adequately, then everybody would use ns1, and nobody would use ns5, unless ns1-ns4 were down.

I want the 5th server only to be queried for dns if the first 4 are completely out. Please let me know if this is how authoritative nameservers are designed to be used.

Thank you!
-Adam
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Question by:ajmco
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ravenpl earned 500 total points
ID: 35092832
> Can I count on this order to remain intact?
No, the usual/default case for dns is random load balancing - in other words, if registrar is asked for nameservers for Your domain it will return a random order list of them. The client(resolver) should then try them first to last.
To verify simply issue few times (under any linux or similar): host -t ns yourDomain.tld # You'll see the random ordered replies

> I want the 5th server only to be queried for dns if the first 4 are completely out.
Ask Your registrar if he can do it for You.
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by:giltjr
ID: 35094480
I second ravenpl's answer.  

The idea behind the load balancing is that a single DNS server is not over whelmed with all of the requests.  If DNS requests were sent to server in the "order listed", then the 1st one listed would get swamped and have performance problems.

I don't think you can have a "standby" DNS server that activates only when the other are down.  Part of the problem is that in the TCP/IP world you don't know something is down until you try to connect to it.

The closest thing you could possibly do is to have a SINGLE IP address for your name server, put your 5 boxes behind a load balanacer. Setup the load balancer to to balance between 1-4 and only use 5 if 1-4 are down.
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