All,
I am not entirely sure how best to describe this, but here goes. Suppose you have two WAN links (for redundancy), such as two ADSL lines from different ISP's. So each link has a different subnet. What is the best way to set up DNS? Here's what I am wondering. I would assume you'd have a DNS server on each WAN link. Normally if someone wants to browse your site, either DNS server will respond, and therefore, they'd be able to reach your site from either WAN link. Suppose one of your WAN links goes dead? Wouldn't they not be able to hit that DNS server, and time-out on the request? Is there some way to notify their systems that if that DNS server happens to be unavailable to check the other DNS server? I am sure this is a really fundamental question that I should probably know the answer to by now, but perhaps someone could point me in the right direction?

Thanks!
-P

It's called DNS RR (Round Robin). Basically you setup a DNS server(s), either your own or your ISP's, and your assign the two records of the host name in your zone file:

www IN A 216.10.10.1
IN A 64.20.20.2


If you do this yourself you will need to setup your DNS server as the authority of your domain. You will need change those settings with your registrar.

If you do it through your ISP then you can add the records in their zone files.

Now when www.yourdomain.com is resolved it will try the first address and if not found it will try the second; it will round robin the addresses so you need to make sure the services are clustered.