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Understanding Active Directory, Part V

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One of the strengths of the Active Directory is its conformity to several important industry open standards and naming conventions, permitting greater interoperability of Windows 2000 within a heterogeneous environment. Although the interplay of the Active Directory with non-Windows 2000 directory services is far from seamless, it does provide the potential for greater multi-operating system information exchange.
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Open Standards Support and Naming Conventions

One of the strengths of the Active Directory is its conformity to several important industry standards and conventions, permitting greater interoperability of Windows 2000 within a heterogeneous environment. Although the interplay of the Active Directory with non-Windows 2000 directory services is far from seamless, it does provide the potential for greater multi-operating-system information exchange. The Active Directory embraces the Domain Name System (DNS), and supports the Lightweight Directory Access Protocol (LDAP). DNS resolves domain names to IP addresses in the Internet and within closed intranets. LDAP extends directory service interoperability by providing directory access across heterogeneous networks. In addition to its support for these protocols, the Active Directory also utilizes industry standard naming conventions, which are listed in Table 1.

Table 1—Industry Standards Used by the Active Directory

Standard

Reference

Description

DNS Dynamic Update

RFCs 2052, 2163

Dynamic host name management

Dynamic Host Configuration

RFC 2131

Network IP address management

Protocol (DHCP)

Kerberos, v5

RFC 1510

Authentication

Lightweight Directory Access

RFC 2251

Directory access

Protocol (LDAP) v3

LDAP 'C'

RFC 1823

Directory API

LDAP Schema

RFCs 2247, 2252, 2256

Directory schema

Simple Network Time

RFC 1769

Distributed time services for networks

Protocol (SNTP)

Simple Mail Transfer

RFC 821

Message transfer

Protocol (SMTP)

Transfer Control Protocol/

RFCs 791, 793

Network transport protocols

Internet Protocol (TCP/IP)

X.509 v3 certificates

ISO X.509

Authentication


NOTE

The Active Directory also supports the Hypertext Transfer Protocol (HTTP), which defines the methods of displaying information on a Web browser. Objects within the Active Directory can be displayed as HTTP pages.

Active Directory and DNS

The DNS resolves names within a TCP/IP network. That is, it translates a domain name such as EntCert.com into an IP address, and vice-versa. All Active Directory domain names follow the DNS naming convention, allowing easy access to the IP address of Active Directory objects that use DNS names. Windows 2000 DNS is a Microsoft-developed implementation, not a port of public domain software, but it does follow the RFC and BIND standards.

In spite of its long-time use in UNIX and other operating systems, DNS is a long way from being an automated or self-managed service. Maintenance of DNS is often viewed as a system administration burden. In most legacy environments, the system administrator labors with manual manipulation of flat text files. Most recently, the advent of the Dynamic DNS protocol has emerged to streamline the use and maintenance of this popular name locator. Windows 2000 bundles its own version of Dynamic DNS that tests and updates DNS registration across defined intranets and the Internet.

Although Microsoft bundles its own version of Dynamic DNS, other third-party versions with base-level functionality are also supported by Active Directory. By "base-level functionality," we refer to the requirement for the third-party DNS to support both Dynamic DNS and Service Resource Records (SRV RR) technology, as defined by RFC 2052 and 2136 and Bind 8.1.2. Active Directory with Dynamic DNS installed will check TCP/IP addresses across the network to make data correction and appropriate deletions. Local services are published through the Service Resource Records (SRV RR) in DNS with the following structure:

<service>. <Protocol>. <Domain>. 

For example, if a commercial version of sendmail were used to support the EntCert.com domain, the SRV RR would then look like this:

<sendmail>. <Tcp>. <EntCert.com>. 

Because Active Directory can support other third-party DNS programs, the actual infrastructure can take one of three basic forms:

  • Microsoft's own Dynamic DNS is installed and utilized by the Active Directory.

  • A third-party Dynamic DNS that supports SRV RR is used by the Active Directory.

  • Microsoft's Dynamic DNS installed as a back-end via a delegated zone from the older server, thereby providing new support for SRV RR and Dynamic DNS technology features.

In addition to interoperability with DNS servers in other operating systems, the Active Directory's Dynamic DNS reduces other administrative burdens. With the release of Windows NT 4.0, Microsoft integrated DNS with its own Windows Internet Naming Service (WINS). Within a Windows NT environment, clients may have fixed IP addresses, or can be assigned an address at startup that employs the Dynamic Host Configuration Protocol (DHCP).

Interoperability Issues

In many cases, UNIX-based DNS servers will exist within an enterprise. A desire to maintain DNS on UNIX will often prevail due to the established investment and maintenance of these servers. Although Windows 2000 supports this approach, Microsoft contends that there are a number of compelling reasons for the utilization of Windows 2000 DNS server in heterogeneous environments. The basis of their argument is the support of the latest RFC standards that may not be available with older versions of UNIX. The UNIX system can meet Active Directory DNS requirements by upgrading the BIND DNS server to version 8.1.2 or later. Support for SRV resource records is also required. Dynamic updates are desirable, but are not compulsory.

Where non-Windows 2000 DNS servers are to be used for the root zone, Windows 2000 DNS services should also be employed to support Active Directory registration and updates. This may require modification of the other DNS namespace design. Under one scenario, you can establish a new subdomain to root the first Active Directory domain. For example, if the established root domain name is EntCert.com, the Active Directory subdomain might become win2k.EntCert.com. Another approach is to create multiple subdomains based on the second-level domain that supports Active Directory registration. Both scenarios involve the delegation of the DNS namespace into additional zones.

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