Chapter 29. Network Name Resolution / Upgrading and Repairing Networks

Computers use hardware addresses when exchanging data on the local subnet. These addresses are burned into the network adapter and are often referred to as MAC (Media Access Control) addresses. MAC addresses produce a flat address space, so network protocols, such as IP, are typically used to create a hierarchical address space. However, for humans, both MAC and IP addresses (or IPX/SPX addresses, for that matter) are difficult to remember. Names are convenient for use by humans who have to operate computers. So, besides identifying a computer or network device using a protocol address, it's also important to be able to give a name to a computer, a network device, or a service, and then have that name resolved to the address so that data communications can take place on the network.

Understanding how name resolution works on your network will better prepare you to troubleshoot the problems users encounter when trying to locate resources.

This chapter deals with standard name resolution techniques ranging from the simple LMHOSTS files to the Windows Internet Name Service (WINS) for NetBIOS names and HOSTS files and the Domain Name System (DNS) service for IP names. For most networks, such as those that have Unix, Linux, or Windows computers, the name resolution methods described in this chapter will suffice. However, Windows 2000, Windows XP, or Windows Server 2003when deployed using the Active Directoryadds a whole new dimension to name resolution. The Active Directory stores objects that can represent everything from a user account to a resource on the network, such as a computer or a printer. If you employ Windows 2000 or 2003 Servers in your network, you might find Chapter 30, "Using the Active Directory," to be an important resource.

In a similar fashion, Novell Directory ServicesNDS, now called the eDirectoryis a directory-based solution that maintains information about and provides access to every resource on the network.

Note

Active Directory and eDirectory can be used to quickly locate resources on the network. They do, however, take the concept of name resolution farther down the road in that you can locate a resource using its name as well as by specifying attributes of the resource you need to use. For example, if you don't know the name of a printer, directory servers enable you to specify search criteria to locate it (or any resource). In the case of a printer, you can specify that it be a color printer, a printer stationed at a particular location, or even such criteria as whether it prints in duplex mode or has three-hole paper installed.

Another important factor to consider when using a directory service is that it is not a replacement for the name resolution techniques described in this chapter. This is easy to understand when you consider that that, in a Windows Server environment, a client computer uses a DNS entry to locate a domain controller so that it can authenticate itself to the network before it can even begin to use the Active Directory.

For Unix/Linux systems, the upgrade path from the older HOSTS file was Sun's Network Information System (NIS), which was formerly called Yellow Pages, until trademark issues forced a name change. Later versions of NDS, which provide additional security and other facilities, are now called NFS+.

You'll find both NIS commands as well as commands that start with the letters yp on some Unix systems. Today there is a growing movement to move authentication and other information to an LDAP-based directory server. A number of LDAP-enabled directory servers can be used with different operating system platforms, and a quick search on the Internet can reveal a lot of information. In addition, there's an open source version of an LDAP server that you can review at http://www.openldap.org. For a basic overview of LDAP, see Appendix D, "The Lightweight Directory Access Protocol."

When working in a multiprotocol environment, there are several ways in which you can create a single namespace using an LDAP-enabled directory to provide a single directory service for Windows, Unix, Linux, and NetWare clients. You'll find a discussion of these topics and the utilities that can help you get there in Part XI, "Migration and Integration," later in this book.