38 DNS C ONFIGURATIONWhen configuring DNS, go to these sections for information you are interested in:■ “DNS Overview” on page 609■ “Configuring the DNS Client” on page 611■ “Configuring the DNS Proxy” on page 612■ “Displaying and Maintaining DNS” on page 612■ “DNS Configuration Examples” on page 613■ “Troubleshooting DNS Configuration” on page 618n This document only covers IPv4 DNS configurations. For IPv6 DNS configurationinformation, refer to “IPv6 Basics Configuration” on page 655.DNS Overview Domain name system (DNS) is a distributed database used by TCP/IP applicationsto translate domain names into corresponding IP addresses. With DNS, you canuse easy-to-remember domain names in some applications and let the DNS servertranslate them into correct IP addresses.There are two types of DNS services, “Static Domain Name Resolution” on page609 and “Dynamic Domain Name Resolution” on page 609. Each time the DNSserver receives a name query it checks its static DNS database before looking upthe dynamic DNS database. Reduction of the searching time in the dynamic DNSdatabase would increase efficiency. Some frequently used addresses can be put inthe static DNS database.Static Domain NameResolutionThe static domain name resolution means setting up mappings between domainnames and IP addresses. IP addresses of the corresponding domain names can befound in the static DNS database when you use applications such as telnet.Dynamic Domain NameResolutionResolving procedureDynamic domain name resolution is implemented by querying the DNS server. Theresolution procedure is as follows:1 A user program sends a name query to the resolver in the DNS client.2 The DNS resolver looks up the local domain name cache for a match. If a match isfound, it sends the corresponding IP address back. If not, it sends a query to theDNS server.3 The DNS server looks up the corresponding IP address of the domain name in itsDNS database. If no match is found, it sends a query to a higher DNS server. Thisprocess continues until a result, whether success or failure, is returned.
