Diving into DNS sub-domains

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wink2k   IN   NS      ns1.win2k.itworld.com.

wink2k   IN   NS      ns2.win2k.itworld.com.

wink2k   IN   NS      ns3.win2k.itworld.com.

wink2k   IN   NS      ns4.win2k.itworld.com.

wink2k   IN   NS      ns5.win2k.itworld.com.

Since those NS records reference host names rather than IP addresses, I will need to add host records for each of the five name servers so other servers (and clients) will know how to reach these name servers to resolve their queries. Often referred to as "glue," those host records are the adhesive between the parent domain and the subdomain. In my example, I would add the following five host records:

ns1.win2k.itworld.com.   IN   A

ns2.win2k.itworld.com.   IN   A

ns3.win2k.itworld.com.   IN   A

ns4.win2k.itworld.com.   IN   A

ns5.win2k.itworld.com.   IN   A

Notice that in my example, each host resides on a different IP subnet. This represents distributed placement of those name servers, as would be the case in a distributed environment.

You will also need to add PTR records to each host's corresponding reverse-lookup zone. For now, let's assume that we will leave these reverse-lookup zones on the Unix-based name servers. (I'll discuss the merits of hosting these on Windows 2000 in a future column.)

Next, you will need to set up your new zone, win2k.itworld.com, on your first Windows 2000-based name servers. You can do this from Windows 2000's DNS management console. After setting up that zone, you should then configure your Windows 2000 name server to use your Unix servers as DNS forwarders. This simply instructs the server to query your Unix servers if it is not familiar with the DNS record for which a client is asking. In short, it will allow forward lookups from the Windows 2000.itworld.com domain to the itworld.com domain. For optimal response times and network efficiency, you should indicate as forwarders the Unix servers that are closest to your Windows 2000 server in terms of network cost. For redundancy's sake, you should specify at least two or more forwarders.

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