Operation Manual – DNSH3C S7500 Series Ethernet Switches Chapter 1 DNS Configuration1-1Chapter 1 DNS ConfigurationWhen configuring DNS, go to these sections for information you are interested in:z DNS Overviewz Configuring Static Domain Name Resolutionz Configuring Dynamic Domain Name Resolutionz Displaying and Maintaining DNS Configurationz Troubleshooting DNS Configuration1.1 DNS OverviewA domain name system (DNS) is a distributed database system that provides domainname-to-IP address mappings for TCP/IP applications. With DNS, users using IPapplications can directly use meaningful easy-to-remember domain names, which willbe resolved and mapped to corresponding IP addresses by DNS servers.There are two types of DNS resolution, static and dynamic. When a name query isreceived, static resolution is first performed to check the static DNS list. If the staticresolution fails, dynamic resolution is performed to look up the dynamic DNS list.Because dynamic resolution needs the cooperation of a DNS server and may takesome time, you can put some commonly used domain names into the static DNS list toimprove resolution efficiency.1.1.1 Static DNS ResolutionWith static DNS resolution, you can manually configure some name-to-addressmappings in the static DNS list, and the system will search the static list forcorresponding IP addresses when users use domain names for some applications(such as telnet).1.1.2 Dynamic DNS ResolutionI. Resolution procedureThe procedure of dynamic DNS resolution 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 DNS cache for a match. If a match is found, itreturns the corresponding IP address to the user program. If not, it sends a queryrequest to the DNS server.3) The DNS server looks up its database for a match. If no match is found, it sendsthe request to its parent DNS server. If the parent DNS server does not have theinformation, it sends the query to another server. This process continues until a
