DNS is Down - Trying to understand Backup NS

[ScubaAddict]

My domains are registered with namebargain.com. I use their 5 DNS servers. 3 times in the past year, all 5 of their NS's go out of commision for whatever reason (Today they claim DoS attack on their DNS servers).

Now I've been reading about backup DNS, but it just isn't clicking. If I get a backup, how does the client know "hey namebargain DNS is down, go over to freeDNS (or whatever)".

Also... How do I set it up in both NameServers? ie.

DNS1: ns1.namebargaindns.com
DNS2: ns1.freedns.com
DNS3: ns2.namebargaindns.com
DNS4: ns2.freedns.com

etc...?

Do clients check the first and if it fails how do they know about the second? or is it hit/miss - 50% of requests go to freedns, other 50% go to namebargaindns, so 50% fail to resolve?

Thanks for spelling this out to me!

[edited by: ScubaAddict at 6:28 pm (utc) on Aug. 9, 2007]

[jtara]

It's hit-or-miss. There is no guarantee that name servers are visited in the order listed. Connection to one nameserver fails, then after a timeout the resolver tries another, randomly. The initial connection is also random. Obviously, your users would experience delays (but generally only on initial connection) if one of the providers is down.

Yes, on average, over time, given an equal number of nameservers on each provider, 50% would be resolved by one, 50% by the other.

Better just to get a more reliable DNS provider. I certainly wouldn't be using one that has had five servers down multiple times. I'm not even sure how that happens - they should all be in different physical locations.