Linux Name Services

Chapter 4: Linux Name Services

One of the most fundamental services on a TCP/IP network is

translates hostnames into IP addresses. In Chapter 3, "Login Services," we configured telnet and

ftp. Without name service, a user connecting to crow enters

name service. It is the service that

telnet 172.16.5.5

With name service, that same command is

telnet crow

The result is the same. In either case, the user connects to the host at address 172.16.5.5. But most

users prefer hostnames because they are easier to remember and easier to use. This is particularly

true in the global Internet. It is possible to guess that http://www.sybex.com/ is a valid name, but

there is no intuitive way to guess the address 206.100.29.83.

Linux systems use two techniques to convert hostnames to addresses: the host table and the

Domain Name System (DNS). The /etc/hosts file is a table that maps names to addresses. It is a

simple text file that is searched sequentially to match hostnames to IP addresses. The Domain

Name System is a hierarchical, distributed database system with thousands of servers across the

Internet, handling name and address queries. DNS is far more important than the host table for the

operation of the Internet, but both services play a role. This chapter's discussion of name services

begins with a quick look at the host table.