3.8 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 Service (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 DNS, which superceded the host table as a TCP/IP standard, does scale.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), and Multipurpose Internet Mail 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 to move the mail from the server to the end system where it is read by the user. SMTP can only deliver 7-bit ASCII data. MIME extends the TCP/IP mail system so that it can carry a wide variety of data.

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

RARP

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.

BOOTP

Bootstrap Protocol provides a wide range of configuration values.

DHCP

Dynamic Host Configuration Protocol extends BOOTP to provide 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.

Network File System (NFS) is the leading TCP/IP 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.

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.