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So, here's the scenario:

In our environment (Windows 2003 domain) we have a host X in production and X's twin in DR (call it Y). In the current version there is a CNAME abc that points to X. Problem is, what I really want is that Prod-site hosts resolve abc to X and DR-site hosts resolve abc to Y.

They are separate sites in AD but it's one domain. This is not a web server so we can't use gimmicks like http-redirect.

Any ideas?

Vincent Magnotta
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3 Answers3

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Netmask ordering (which is enabled by default) should accomplish the objective, if you use A records rather than CNAME records.

joeqwerty
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  • This is a much better solution, as long as the application using the server obeys the ordering that the DNS server replies with. See [here](http://support.microsoft.com/kb/842197) if you need to tweak the mask length that constitutes 'proximity'. – Shane Madden Jan 25 '12 at 04:00
  • Since none of the A records is actually the primary address, I should make sure no PTR record matches these since they are effectively aliases, right? @ShaneMadden's link is excellent since my next question was what constitutes proximity in this context. – Vincent Magnotta Jan 25 '12 at 06:45
  • @VincentMagnotta `PTR` records shouldn't be an issue, unless your application checks them for some crazy reason. Feel free to make the `PTR` record for every address match the `A` record's name. – Shane Madden Jan 25 '12 at 06:47
  • PTR records aren't required for AD and I've yet to see an application that uses them so they shouldn't be an issue. – joeqwerty Jan 25 '12 at 11:42
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You can accomplish this by, basically, cheating a bit to create different perspective of DNS for different systems.

I'm going to assume that you have a DC in both sites, since you've got different AD sites for them. What you'll also need to do, if you haven't already, is to make sure that every system in each site is pointing to a DC in its own site.

Once that's done, create a zone on every DC for the DR record - but don't create it as AD-integrated. Say you're looking to make importantserver.example.com resolve to the local copy - make it a CNAME in the AD integrated zone, pointing to the standalone zone; say, importantserver.dr.example.com.

Records in that zone can and will be different between the sites, since they're not replicating. Have it resolve to server X in site X and server Y in site Y, and you've got the resolution topology you're looking for.

..Or just set up BIND with a split view.

Shane Madden
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I'm not Windows/AD guy but this seems like a job for http://en.wikipedia.org/wiki/Split-horizon_DNS

RJS
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