Chapter 4: Managing the Exchange Organization Topology

Chapter 4 - Managing the Exchange Organization Topology
Monitoring and Managing Microsoft Exchange 2000 Server
by Mike Daugherty
Digital Press 2001

4.2 Namespace and name resolution

4.2.1 Domain name system (DNS)

Exchange 2000 is a network-based product that resides in the applications layer of the TCP/IP Reference Model. As a network-based product, it is highly dependent upon the network transport and protocol support provided by the underlying network. While the Exchange server packages e-mail messages for delivery, it is actually the underlying network that transports the message to the recipients environment. Client systems also use the network infrastructure to communicate with the Exchange servers. Before a client or server can communicate with another server, it must be able to translate the target servers name into an address. A properly functioning name resolution system is an essential component of any networked environment.

Windows NT 4.0 and Exchange Server 5.5 used two methods of name resolution:

• Windows Internet Naming Service (WINS) . WINS provided Net-BIOS over TCP/IP (NetBT) name resolution for Windows NT 4.0. WINS was the preferred name resolution method for Windows NT 4.0 primarily because is supported dynamic name registration.

• Domain Name System (DNS) . DNS provided Winsock-based name resolution. By default, both Exchange and Outlook used DNS for name resolution since they used the Winsock layer for communications.

Windows 2000 and Exchange 2000 use DNS for name resolution. Neither Windows 2000 nor Exchange 2000 will operate if you do not have a DNS service running on your network. While Exchange has always relied upon DNS, the extensive use of DNS by the operating system is new. All domain names and the Windows 2000 namespace are stored in DNS. The location of domain controllers is stored in DNS using Service Resource Records (SRV-RR) to map service names . DNS, rather than WINS, is now used for logon validation and domain validation.

DNS is primarily used to record the names and locations of systems and services, while the Active Directory is used to store object and attribute information. Windows 2000 uses LDAP to find Active Directory objects and elements. Table 4.5 compares the relative advantages of DNS and LDAP for locating information.

The DNS naming scheme is standards-based (RFC 1034 and RFC 1035) and provides maximum interoperability with Internet technologies. The DNS used in your Windows 2000 environment must also support Service Resource Records (RFC 2052). It is also advisable that the DNS you choose also support the following features:

• Dynamic Update (RFC 2136) . With dynamic updates, the netlogon service on the domain controller will automatically register domain services and sites. This reduces the need to manually update DNS records and reduces human errors.

• Incremental Zone Transfers (RFC 1995) . Incremental Zone Transfers reduce the network bandwidth requirements for replicating information to all DNS servers.

The DNS service that is supplied with Windows 2000 supports all of these features.

Your DNS strategy needs to be planned early and implemented before you deploy Windows 2000. Carefully consider the names you will use because after you choose and deploy the names, any changes may be difficult.

The DNS root domain name will be the name used for the root of your Windows 2000 forest. The root domain name should be meaningful, available, registered, and stable. Management and legal approval are usually required for DNS root domain names since these are known to the public.

You will need to determine the zones you need to create. You should ensure that you have a zone for each domain so that you can integrate DNS into the Active Directory if you decide to do so at some point, either immediately or in the future.

You also need to consider the names that will be used. Remember that each system will be represented by a fully qualified DNS name (e.g., server89.dallasdomain.compaq.com). The names should be meaningful, but they should also be short because the fully qualified name can become rather lengthy and difficult to use. You should use only characters that are part of the character set permitted for use in DNS host naming. These characters include all letters (both upper case and lower case), numbers , and the hyphen (-).

Table 4.5: DNS and LDAP

Domain Name System (DNS)	LDAP
Hierarchical, distributed, partitioned, replicated Most-used naming service Great for finding systems Not very good for accessing fine-grained attributes Used to find LDAP server that is a domain controller	Emerging standard Great for fine-grained attributes and lookups LDAP is used to access objects inside a domain

Exchange 2000 Server relies upon specific DNS services. Exchange 2000 replies upon Service Resource Records (SRV-RR) to locate domain controllers, global catalog servers, and sites. Exchange does not enter any Service Resource Records for the Exchange servers. Instead, Exchange servers are registered in DNS as Address (A) records, and Exchange 2000 uses these Address records to locate other Exchange servers in the forest. Exchange 2000 also uses DNS Mail Exchanger (MX) records to identify Exchange and non-Exchange mail servers that support different domain namespaces. SMTP (including the Exchange SMTP connector) uses the MX records to locate preferred SMTP mail servers.

In addition, some Exchange 2000 components use Internet Information Server (IIS) Web services. For example, Outlook Web Access (OWA), Instant Messaging, and Conferencing all have an associated namespace. DNS aliases can be used to provide users with a more friendly representation of the namespace.

By default, the Windows 2000 domain name as registered in DNS is used as part of the e-mail address for users within the domain. For example, users in the dallas.compaq.com domain would have users of the form [e-mail]. However, this need not be the case. Although a user s Windows 2000 logon name might be username@ dallas .compaq.com, the generation of e-mail addresses can be controlled using the following procedure:

1. Start the System Manager from the Windows 2000 Start menu by selecting Programs   Microsoft Exchange   System Manager.

2. Select Recipients   Recipient Policies, and then double-click Default Policy to display the Default Policy Properties (Figure 4.11). The E-Mail Addresses tab contains the default e-mail address general rules.

   
   Figure 4.11: The default Policy Properties window

Windows Internet naming service (WINS)

WINS and NetBIOS are still supported by Windows 2000. In fact, Windows 2000 has enhanced WINS by adding manual tombstoning, improved management tools, enhanced filtering, and dynamic record deletion. While Windows 2000 no longer relies upon WINS, WINS is still used by Windows NT 4.0 domain members in a mixed environment and by legacy applications.

You should evaluate your use of WINS. For an existing Windows NT environment that is migrating to Windows 2000, you will need to keep WINS running for coexistence. You should consider how names would be supported in both DNS and WINS because clients may be using either one to access resources.

4.2.2 Active Directory naming contexts

Active Directory naming contexts (NC) define boundaries for holding specific types of AD information. Each naming context partition has its own permissions structure, replication configuration, and other properties. Active Directory has three default naming contexts: Configuration, Domain, and Schema. The following sections briefly describe the three naming contexts and how Exchange 2000 Server uses them.

Configuration naming context

The configuration naming context contains Exchange information such as address list services, addressing templates, display templates, administrative groups, routing groups, connections to other Exchange servers, recipient policies, instant messaging settings, message delivery settings, and Internet message formats. Exchange servers use the configuration naming context to hold most of the Exchange-specific information. Since the configuration naming context is common to all domain controllers within the forest, Exchange servers can query a local domain controller to get this type of information.

Domain naming context

The domain naming context defines the boundaries of the Windows 2000 domain and contains all objects for the domain. The domain NC is unique to each domain within a forest, and this information is replicated only to other domain controllers within the same domain. The domain naming context contains Exchange information such as mailboxes, mail-enabled users, groups, contacts, and public folder definitions.

Schema naming context

The schema naming context contains the class definitions for objects within the Active Directory. The class definitions are the rules that define the attributes that must be included with each specific type of object, the attributes that may be included with each object, and the place within the Active Directory hierarchy that each type of object may be created. When Windows 2000 is installed, a default schema is created that defines all object classes needed by Windows 2000. The schema is extended during the Exchange 2000 installation to add object classes and attributes needed by Exchange.