By Andrej Budja

By today’s network standards, DNS has been around for a long, long time. You’d think it would have been replaced by now. However, DNS is alive and kicking. In fact, it’s become an essential part of every Windows 2000 network. Before you can effectively use DNS and take advantages of its many features, you have to know why Microsoft uses it.

Why do I need DNS?
Look no further than Active Directory (AD) for your reason to know DNS. Every AD domain (and any host computer in the domain) must have a name. When we have to name something, we have to agree on a standard naming system. For example, we have to agree on how many characters we can use and which characters are allowed. For Windows 2000, Microsoft decided to use DNS as its naming standard.
Understanding DNS in Windows NT 4.0”“What’s in a name? Creating a DNS server”“Getting ready for Windows 2000
Namespace definition
All names adhere to the DNS standard. The standard states that a single name (for example, mycomputer) can be up to 63 bytes and that a fully qualified domain name (FQDN), such as, can be up to 255 bytes. The only exception regarding the size of the name is that an FQDN for a domain controller is limited to 64 bytes. We use bytes instead of characters because Windows 2000 also supports Unicode characters that can take up to 3 bytes.

If you remember from Windows NT 4, NetBIOS names are limited to 15 characters. The 16th character is reserved for the NetBIOS suffix. We still have NetBIOS names in Windows 2000, but only for compatibility with lower-level clients (Windows NT 4, Windows 9x, and so on). Another advantage over NetBIOS is that DNS is a hierarchical system, while NetBIOS is essentially flat. This means that a NetBIOS name can be used only once in the whole network, which poses a problem in very large networks with many hosts. Because DNS is hierarchical, we can use one name many times, but only once in a given domain. For example, we can’t have two computers named www in the domain, but we can have one computer named www in the domain and another named www in the domain.

Name resolution
Another reason for using DNS in Windows 2000 is name resolution. If we have a computer name, such as mycomputer, and we want to communicate with that machine, there must be a way to resolve this name to an IP address. Since computers use numbers to resolve addresses, and we’re already using DNS as a namespace definition, it’s logical to use DNS servers for name resolution.

Service resource records
In old non-Windows 2000 networks, we have to know the name of a host if we want to use its resources. For example, if you want to download files from an FTP server, you have to know the name of that server. If we have one or two servers, we can remember their names—but imagine having thousands of servers to choose from. Not only would it be hard to remember all the names, we would also have problems remembering which servers run FTP, which are mail servers, and so on.

DNS solves this problem with special service resource records (SRV RR). These records allow us to query a server by type of service it performs. For example, we could just issue a query for an FTP server and DNS would return all servers that had FTP server software installed.

Active Directory uses SRV RR extensively. Actually, you can’t run AD without a DNS server that supports these records. So the moment a user types a username and password, his or her Windows 2000 client will use DNS and SRV RR to locate the closest domain controller. When the closest domain controller is found, the computer will validate against this controller. This is a great solution if your users travel a lot and use a notebook. There will be no unnecessary traffic over slow WAN links when you have domain controllers on your local network.

DNS is apparently here to stay. Universally accepted and now an integral part of the Windows 2000 network, this naming standard is not going to be replaced anytime soon. So if you aren’t familiar with it, I hope this article has given you some background on why DNS is so important to networks around the globe.

Like DNS, Andrej Budja, MCSE+I, MS MVP, has been around computers for a long time. He likes to learn new technologies and is known as a guy who’s always ready to help. He does this every day in the Microsoft Windows 2000 newsgroups.

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