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3.7. Summary

TCP/IP provides some network services that simplify network installation, configuration, and use. Name service is one such service and it is used on every TCP/IP network.

Name service can be provided by the host table, Domain Name System (DNS), and Network Information Service (NIS). The host table is a simple text file stored in /etc/hosts. Most systems have a small host table, but it cannot be used for all applications because it is not scalable and does not have a standard method for automatic distribution. NIS, the Sun "yellow pages" server, solves the problem of automatic distribution for the host table but does not solve the problem of scaling. DNS, which superseded the host table as a TCP/IP standard, does scale. DNS is a hierarchical, distributed database system that provides hostname and address information for all of the systems in the Internet.

Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP), Internet Message Access Protocol (IMAP), and Multipurpose Internet ail Extensions (MIME) are the building blocks of a TCP/IP email network. SMTP is a simple request/response protocol that provides end-to-end mail delivery. Sometimes end-to-end mail delivery is not suitable, and the mail must be routed to a mail server. TCP/IP mail servers can use POP or IMAP to move the mail from the server to the end system, where it is read by the user. SMTP can deliver only 7-bit ASCII data. MIME extends the TCP/IP mail system so that it can carry a wide variety of data.

Network File System (NFS) is the leading Unix file-sharing protocol. It allows server systems to export directories that are then mounted by clients and used as if they were local disk drives. The Unix LPD/LPR protocol can be used for printer sharing on a TCP/IP network. Samba provides similar file and print sharing services for Windows clients.

Many configuration values are needed to install TCP/IP. These values can be provided by a configuration server. Three protocols have been used by TCP/IP for distributing configuration information:


Reverse Address Resolution Protocol tells a client its IP address. The RARP server does this by mapping the client's Ethernet address to its IP address. The Ethernet to IP address mappings are stored on the server in the /etc/ethers file.


Bootstrap Protocol provides a wide range of configuration values.


Dynamic Host Configuration Protocol replaced BOOTP with a service that provides the full set of configuration parameters defined in the Requirements for Internet Hosts RFC. It also provides for dynamic address allocation, which allows a network to make maximum use of a limited set of addresses.

This chapter concludes our introduction to the architecture, protocols, and services of a TCP/IP network. In the next chapter, we begin to look at how to install a TCP/IP network by examining the process of planning an installation.

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