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Full disclosure: I'm not an AD guy so this might pertain to something obvious. I apologize in advance if that's the case - I did try searching for prior questions regarding this.

I'm installing a Linux-based web application server in an AD environment (vanilla CentOS 5.x - no special integration with AD). The app performs LDAPS queries against Global Catalog servers. In order to discover which AD server to talk to, it performs a DNS Lookup for A records pertaining to the AD domain (foo.int). This specific query appears to be failing (I'm still looking into it).

In the meantime though, I'd like to confirm a few things:

  • If I'm pointing the Linux server to Microsoft DNS servers, and query for the AD domain (foot.in), is it reasonable to assume that I should get A records pointing to some GCs?
  • Is the availability of A records for GCs something that is pretty standard? Or is this something that varies from environment to environment? In other words, are there some environments that just don't have internal A records published at all for DCs?
  • Are these specific records something that is automatically managed/updated, or are they manually added/edited by admins?
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You can't know which DC is a GC by querying for the DC A records. You need to query for the GC SRV records. –  joeqwerty Dec 16 '13 at 20:41
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up vote 7 down vote accepted

If I'm pointing the Linux server to Microsoft DNS servers, and query for the AD domain (foot.in), is it reasonable to assume that I should get A records pointing to some GCs?

No, what you will get is all Domain Controllers in the domain not necessarily just the Global Catalog Servers. If you just want the Global Catalog servers you can query _gc._tcp.<your_AD_FQDN> or you can query _gc.<your_site_name>._sites.<your_AD_FQDN> if you just want the GCs in a specific site. This is actually an SRV type record.

Is the availability of A records for GCs something that is pretty standard? Or is this something that varies from environment to environment? In other words, are there some environments that just don't have internal A records published at all for DCs?

All DCs will have an A record, It should be auto registered. But it's possibly that if auto-dns registration is turned off for the NIC that there will be no A record if someone didn't do it manually. AD will be broken if this stuff is turned off.

Are these specific records something that is automatically managed/updated, or are they manually added/edited by admins?

The _sites, _msdcs, _tcp, and _udp zones are managed automagically. The A records should be too, as long as someone hasn't done something silly with the config to turn this stuff off.

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