Chapter Summary

   

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Host name resolution methods are used to map host names to IP addresses and vice versa. The most widely used method is the Domain Name System (DNS). Other than this method, the /etc/ hosts file or simply hosts and NIS are also used in different circumstances. The hosts file contains a listing of IP addresses and host names. Aliases can also be used in the hosts file. It is scanned from top to bottom in the resolution process and the first matching entry is chosen .

A DNS consists of three parts : the name space, the resolver, and the name server. The name space is a hierarchical data structure used to assign host names. The resolver library routines are used to select a particular name resolution method. The name server keeps a record in its data files of all hosts in a domain and resolves a host name. Three types of name servers are used. The primary name server has authority over a domain name, while secondary name servers are used for backup to the primary name server. The caching server does not have any data files and is used for load sharing only.

Name server data files are created using the hosts_to_named command line utility. It reads the /etc/hosts file and generates the configuration and data files for primary, secondary, and caching servers. Configuration files for secondary and caching servers are then transferred to desired machines from the primary name server. A secondary name server keeps its files updated by consulting the primary server after defined intervals of time.

A DNS client has the /etc/resolv.conf file consisting of a list of local domain names and name servers. The /etc/nsswitch.conf file is used to set up the order in which host name resolution services are used. The nslookup command can be used to test and resolve host names using a DNS.

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