Chapter 31. Host Name Resolution and Domain Name Server

Chapter Syllabus

31.1 Host Name to IP Address Mapping

31.2 Name Resolution Methods

31.3 Introduction to the Domain Name System

31.4 Configuring the Primary DNS

31.5 Configuring the Secondary DNS

31.6 Configuring the Caching DNS

31.7 Configuring the DNS Client

31.8 Using SAM to Configure DNS

A computer on a TCP/IP network is known by its IP address. Data communication among hosts on a network takes place through IP data packets, also known as IP datagrams, which contain source and destination IP addresses. Keeping in mind the complexity of large IP networks like the Internet, it is not possible for users to remember IP addresses of all servers. To solve this problem, convenient and easy-to-remember names are assigned to hosts in addition to IP addresses. When using the network services discussed in the last chapter, users usually use the host name of the server machine on the command line instead of the IP address. Before starting a communication session, this host name is mapped to its IP address. Host name resolution is a process used to map a host name to its corresponding IP address for communication purposes.

Different techniques are used for host name resolution. The simplest one is the use of the /etc/hosts file. This is a text file that maps a host name to its IP address. This technique is not practical as networks grow larger because this file has to be maintained on all systems on the network. Sun Microsystems has developed a name resolution system known as the Network Information Service (NIS). However, this service has limitations and can't be used on the Internet. The most widely used host name resolution system is the Domain Name System, commonly know as DNS. It can be used on a local network as well as on the Internet. One or more servers are used to keep a record of host name mapping. These servers are called domain name servers. DNS is a hierarchical approach to host name assignment and resolution where a domain name may be assigned to an entire organization and subdomain names can be used for different departments within the organization.

DNS is the default method used on the Internet for name resolution. Internet domains follow a well-defined hierarchy. Every domain name falls under one of the predefined top-level domain names. Root name servers on the Internet have information about a domain name or a pointer to another server that can be used to get that information. If a local domain name server is not able to resolve a host name, it contacts one of the root name servers to get information about another domain name server that can provide the desired information.

Three types of domain name servers are used. The primary domain name server is the main contact for host name resolution inside a domain. The secondary domain name server is used in case a primary name server goes down for any reason. The secondary name server(s) keep their data updated by polling primary servers from time to time. Secondary name servers are also used for load sharing on heavily loaded networks. A third type of domain name server is the caching domain name server, which is used to resolve host names but does not have its own data base files.

A DNS can be setup on HP-UX using command line utilities as well as SAM. The named daemon runs as a server process for a DNS and listens to TCP port 53 for incoming requests . At startup time, this daemon reads its configuration file, /etc/named.boot , where names of the domains and directory containing data files are specified. If the server is being used as a secondary name server, it reads configuration data from the primary DNS at boot time.

This chapter starts with an introduction to the host name resolution process and the methods used for this purpose. An introduction to the domain name system is presented. After that, you will learn how to configure primary, secondary, and caching domain name servers. In the next part you will learn about the configuration and testing of a DNS client. In the last part of the chapter, you will use SAM to configure a DNS server.

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