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OS X 10.5+ has some slightly odd resolver configuration to work around broken networks. It's described here.

The problem I'm having is that our network doesn't rely on brokenly using .local domains over unicast DNS, but instead relies on mDNS for most internal lookups. This works fine for most of our systems, but we would like to have some subdomains too. Sadly this breaks for all our OS X users because of this feature

Host names that contain two or more labels in addition to local, for example "server.domain.local", are resolved using a DNS server by default.

Which results in our subdomains getting looked up on the unicast DNS server instead which doesn't know how to resolve .local addresses at all.

The support article claims that this is default behavior, which to me suggests it's a configurable thing somehow but I can't figure out how to get this to act like 10.4 and just use mDNS for all .local lookups.

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Mac OS X has a pluggable resolver library. This means that you can write your own resolver that gets layered on top of the existing resolver stack. In fact, Unicast DNS and mDNS are entirely separate layers that are stacked together.

The default behavior described by Apple is really intended to mean the default stack. The only way I know of to change this behavior is to write a resolver plug-in that will behave the way you want.

If this sounds like something you want to try, I haven't a clue as to how to do it. However, the POW web server produced by 37signals includes a resolver plug-in written in Ruby. POW is open source, so you may be able to start here (assuming you or someone you know, knows Ruby).

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I know it's handled by mDNSResponder on OS X but I can't find anything relating to this particular feature in the source so far. Recompiling mDNSResponder or writing a whole new layer isn't really an option. – Alex Apr 27 '11 at 17:41

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