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Planning, Implementing, and Maintaining a Network Infrastructure

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This chapter is from the book

Terms you'll need to understand:

  • Active Directory integrated zone

  • Conditional forwarding

  • Domain name service (DNS)

  • DNS forwarder

  • DNS resolver

  • DNS Security (DNSSEC)

  • DNS slave server

  • Fully qualified domain name (FQDN)

  • Iterative query

  • Leaf

  • Recursive query

  • Secure dynamic update

  • Standard primary zone

  • Standard secondary zone

  • Stub zone

  • Top-level domain (TLD)

  • Tree

  • Zone

  • Zone transfer

Techniques you'll need to master:

  • Plan and implement a DNS namespace, the correct DNS zone type, DNS forwarders, and DNS security

  • Integrate with third-party DNS servers

Just a few years ago, TCP/IP was not the king when it came to network communications protocols. Windows NT 4.0 relied on the venerable NetBIOS Extended User Interface (NetBEUI) protocol by default, and NetWare servers could be counted on to understand only IPX/SPX. With the recent widespread adoption of the Internet by the masses, TCP/IP slowly started to creep into private networks of all sizes and purposes. Administrators and network designers began to see the power and flexibility that TCP/IP offered them, and Microsoft and Novell took note of the shift. It wasn't long before all operating systems provided support for TCP/IP, but it still was not the networking protocol of choice. With the introduction of Windows 2000, Microsoft made TCP/IP and the domain name system (DNS) integral parts of Windows Active Directory networks. But how did DNS come into the picture all of a sudden?

If you have ever connected to a Web site by name, you have used DNS. DNS is a service used on the Internet for resolving fully qualified domain names (FQDNs) to their actual Internet Protocol (IP) addresses. For example, suppose you are preparing to take the latest Windows Server 2003 certification exam. You've asked your coworkers what the best study guide available is, and they recommend that you check out Que Publishing's Web site to see what is available. Your obvious question is, "Where can I find Que Publishing's Web site?" Before DNS, the answer would be 165.193.123.44. If you are like most people, you'll remember that number for less than 30 seconds and will probably never find Que Publishing's site (or get that study guide you were looking for).

DNS puts a user-friendly face on that obscure numeric address. With DNS, your friend can tell you to go to http://www.quepublishing.com, and the DNS infrastructure of the Internet will translate the name to the correct address, 165.193.123.44. It's like a series of interconnected phone books. You put in a name, and it gives you the correct number. Fortunately for those of us with a limited ability to memorize strings of numbers, the Internet community recognized the benefits of a name-resolution system as a critical part of the infrastructure that would make up the original Internet architecture—and DNS was born.

The DNS Namespace

As we've discussed, you probably have already used DNS, whether you are familiar with the underlying mechanism or not. Domain names are easy to use and remember: The ease at which you can access a Web site using domain names (such as http://www.microsoft.com or http://www.quepublishing.com) is a built-in simplicity that comes at a price; the DNS namespace is complex. DNS names are created as part of a hierarchical database that functions much like the directories in a file system. Hierarchies are powerful database structures because they can store tremendous amounts of data while making it easy to search for specific bits of information. Before examining the specifics of the DNS namespace hierarchy, let's review some rules about hierarchies in general.

NOTE

Microsoft's Active Directory Service is an excellent example of a hierarchical database. Of course, given that the hierarchy is created on top of the existing rules for a DNS namespace, the information on the DNS hierarchy directly relates to the construction of Active Directory.

Hierarchies

Before getting into the details of a hierarchy, we should introduce some terms:

  • Tree—This is a type of data structure with each element attached to one or more elements directly beneath it. In the case of DNS, this structure is often called an inverted tree because it is generally drawn with the root at the top of the tree.

  • Top-level domain (TLD)—TLD refers to the suffix attached to Internet domain names. There are a limited number of predefined suffixes, and each one represents a top-level domain. The more popular TLDs include .COM, .EDU, .GOV, .MIL, .NET, and .ORG.

  • Node—A node is a point at which two or more lines in the tree intersect. In the case of DNS, a node can represent a TLD, a subdomain, or an actual network node (host).

  • Fully qualified domain name (FQDN)—A domain name that includes all domains between the host and the root of DNS is an FQDN. For example, http://www.microsoft.com is an FQDN.

  • Leaf—A leaf is an item at the very bottom of a hierarchical tree structure, and it does not contain any other objects.

  • Zone—A DNS zone is a logical grouping of hostnames within DNS. For example, quepublishing.com is considered the forward lookup zone for Que Publishing. It is where the information about the Que Publishing hosts is contained within DNS.

In DNS, containers called domains hold the information. The hierarchy starts with a root container, called the root domain. The root domain doesn't have a name, so it is typically represented by a single period, as shown in Figure 3.1. The root domain contains pointers to all TLDs, which are directly below the root. These are also sometimes called first-level domains. Lower-level domains are second-level, third-level, and so on. Every domain name has a suffix that indicates which TLD domain it belongs to. There are only a limited number of such domains as defined by RFC 1591. Some of the more common TLDs are discussed in the following list:

Figure 3.1Figure 3.1 This portion of the DNS hierarchy shows the location of two domains in the DNS database in relation to the rest of the DNS database.

  • .COM—Intended for commercial entities, but it has become the overwhelming favorite top-level domain (example of .COM: area51partners.com)

  • .EDU—Intended for higher-education institutions, such as four-year colleges and universities (example of .EDU: berkeley.edu)

  • .GOV—Intended for use by agencies of the U.S. Federal Government (example of .GOV: whitehouse.gov)

  • .MIL—Intended for use by agencies of the U.S. military (example of .MIL: af.mil)

  • .NET—Intended for use by network providers and organizations dedicated to the Internet, such as Internet service providers (example of .NET: ibm.net)

  • .ORG—Intended for nonprofit or noncommercial establishments, such as professional groups, charities, and other such organizations (example of .ORG: npr.org)

NOTE

Two-letter country code TLDs also exist for nearly all countries on the planet. Examples include .US for the United States, .CA for Canada, .JP for Japan, and .UK for the United Kingdom. New TLDs are constantly being added to meet the requirements for new domain names on the Internet. Recent additions include .BIZ and .INFO, among others.

Fully Qualified Domain Names (FQDNs)

As we have discussed, DNS is used to translate a hostname to an IP address. The FQDN name typically looks something like the following:

This is known as the host's fully qualified domain name (FQDN) because it lists the host's precise location in the DNS hierarchy. The DNS name in the example represents the host FILESVR042 in the subdomain CORPORATE (this is frequently a department or division in a company), which is in the subdomain AREA51PARTNERS (this is frequently the name of the company or organization that has registered the domain), which is in the TLD .COM.

TIP

Make sure you have a good understanding of what an FQDN is and how it is represented.

Planning a DNS Namespace Design

Up to this point in our discussion about DNS, we have looked at only the historical and design aspects of DNS—and for good reason. Only by understanding how DNS was created and designed can you effectively plan and implement a DNS design in a Windows Server 2003 Active Directory domain. Because DNS permeates Windows Server 2003, you must deliberately and carefully plan out your DNS namespace before you ever perform the first installation of Windows Server 2003 on a computer.

The following list represents some questions you should ask yourself when planning your namespace needs:

  • Is your DNS namespace to be used for internal purposes only? If so, you can use characters that are not typically used in DNS names, such as those outside of the RFC 1123 standards. An example might be bigcorp.local.

  • Is your DNS namespace to be used on the Internet as well? If you are currently using a corporate DNS namespace on the Internet, or think that you might at any point in the future, you should register your own domain name and conform to Internet naming standards.

  • Will you be implementing Active Directory? The design and implementation of Active Directory on your network plays a critical role in determining how domains should be created and nested within each other. Chapter 7, "Planning and Implementing an Active Directory Infrastructure," examines the relationship between Active Directory and the domain structure in more detail.

You have the following three basic options to consider when planning the DNS namespace you will be using:

  • Use an Existing DNS Namespace—This option uses the same namespace for both the internal (corporate network) and external (Internet) portions of your network. If your domain name is bigcorp.com, you would use this for both internal and external use. Although this method is the easiest and provides simple access to both internal and external resources, it poses additional administrative requirements because an administrator must ensure that the appropriate records are being stored on the internal and external DNS servers as a security precaution.

  • Use a Delegated DNS Namespace—This option uses a delegated domain of the public namespace. If your domain name is bigcorp.com, you might consider using corp.bigcorp.com for the internal namespace. When using this option, the corp.bigcorp.com domain becomes the root of the Active Directory forest and domain structure. Internal clients should be allowed to resolve external namespace addresses; however, external clients should not. Using a delegated DNS namespace provides a namespace that is easy to understand and remember, and that fits in nicely with the existing registered domain name. All internal domain data is isolated in the domain or domain tree, thus requiring its own DNS server for the delegated internal domain. The downside to delegated namespaces is that this adds length to the total FQDN.

  • Use a Unique DNS Namespace—This option uses a completely separate but related domain name for your internal namespace. As an example, if you are using bigcorp.com for your external namespace, you might use bigcorp.net for your internal namespace. This configuration provides the advantage of improving security by isolating the two namespaces from each other. Additionally, the administrative burden is relatively low because zone transfers do not need to be performed between the two namespaces, and the existing DNS namespace remains unchanged. In addition, this prevents internal resources from being exposed directly to the Internet.

Consider the following example of a fictitious company that is in the planning stages of a major worldwide network reorganization and upgrade to Windows Server 2003 Active Directory. Gidget's Widgets, Inc., is a major manufacturer of household goods and already owns the gidgets.com domain name for its Internet Web site. Gidget's makes everything from bath towels to kitchen sinks. Gidget's corporate headquarters are located in the United States, with regional field offices in Canada, Mexico, England, Germany, India, Japan, and Australia. Gidget's corporate structure has the following major departments: Executive, Administrative, Engineering, Manufacturing, Facilities, Sales, Legal, and Information Services. Within each department are one or more individual divisions. How would you go about designing a DNS namespace for the Gidget's Widgets internal network?

You have several options; let's assume for the sake of argument that you are going to first create a delegated domain named corp to serve as the root of the internal network and also as the Active Directory root. Starting with the corp.gidgets.com domain, you could create fourth-level domains by country code. Within these, you could create fifth-level domains, as required, for each of the major departments. You might end up with a configuration that looks something like that shown in Figure 3.2.

If you were a network administrator in the United States working from a computer called GREENGUY42, your FQDN would be greenguy42.it.us.corp. gidgets.com. Of course, you could also design the DNS namespace using continents instead of countries, if desired. When creating DNS namespaces that are several levels deep like the example seen in Figure 3.2, you must keep in mind some general DNS restrictions as outlined in Table 3.1.

No matter what design you settle on, you must (in most cases) get it right the first time. Redesigning a DNS namespace is a difficult and time-consuming task after the fact, at best. In addition, failing to properly design the namespace for Active Directory compatibility can lead to functionality problems in the future.

Figure 3.2Figure 3.2 Gidget's network has been nicely organized by using countries as third-level domains and major departments as fourth-level domains.

Table 3.1 DNS Name Restrictions

Restriction

Standard DNS

DNS in Windows Server 2003 (and Windows 2000)

Characters

Supports RFC 1123, which permits A to Z, a to z, 0 to 9, and the hyphen (–).

Supports several different configurations: RFC 1123 standard, as well as support for RFCs 2181 and the character set specified in RFC 2044.-

FQDN length

Permits 63 bytes per label and 255 bytes for an FQDN.

Permits 63 bytes per label and 255 bytes for an FQDN. Domain controllers are limited to 155 bytes for an FQDN.


After you've planned out your namespace, you're ready to get down to business and start working out the finer points of your DNS implementation. The next thing you need to plan for is the type of zones you will be using. But what exactly is a zone?

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