310 C HAPTER 11: INTERNET P ROTOCOL (IP)Domain NameSystem (DNS)The Domain Name System (DNS) client allows you to specify a hostnamerather than an IP address when you perform various operations (forexample, when you use ping or traceRoute to contact an IP station).With DNS, you can specify one or more name servers that are associatedwith a domain name. Each name server maintains a list of IP addressesand their associated host names. When you use ping or traceRoute witha hostname, the DNS client attempts to locate the name on the nameservers that you specify. When the DNS client locates the name, it resolvesit to the associated IP address.You can resolve an IP address to a host name or a host name to an IPaddress on a name server. Enter either the host name or the IP address;the DNS client displays the pair.ImportantConsiderationsWhen you set up DNS servers on your LAN, remember the following:n Always set up more than one DNS name server (a primary andsecondary server) so that the lookup service does not have a singlepoint of failure.n If your ISP changes the Classes of Internetwork Service, change theDNS settings on each host that the ISP services.See UNIX NFS documentation for information about how to create andmaintain lists of domain names and IP addresses on the name servers.For information about how to use ping and traceRoute, see Chapter 18in this guide and the IP chapter in the Command Reference Guide.
