3Com Switch 8800 Advanced Software V5 Configuration Guide

DNS CONFIGURATION

When configuring DNS, go to these sections for information you are interested in:

■ “DNS Overview” on page 745

■ “Configuring Static Domain Name Resolution” on page 747

■ “Configuring Dynamic Domain Name Resolution” on page 747

■ “Displaying and Maintaining DNS” on page 747

■ “DNS Configuration” on page 745

■ “Troubleshooting DNS Configuration” on page 751

DNS Overview Domain name system (DNS) is a distributed database used by TCP/IP applications

to translate domain names into corresponding IP addresses. With DNS, you can

use easy-to-remember domain names in some applications and let the DNS server

translate them into correct IP addresses.

There are two types of DNS services, static and dynamic. Each time the DNS server

receives a name query it checks its static DNS database before looking up the

dynamic DNS database. Reduction of the searching time in the dynamic DNS

database would increase efficiency. Some frequently used addresses can be put in

the static DNS database.

Static Domain Name

Resolution

The static domain name resolution means setting up mappings between domain

names and IP addresses. IP addresses of the corresponding domain names can be

found in the static DNS database when you use applications such as telnet.

Dynamic Domain Name

Resolution

Resolving procedure

Dynamic domain name resolution is implemented by querying the DNS server. The

resolution 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 is

found, it sends the corresponding IP address back. If not, it sends a query to the

DNS server.

3 The DNS server looks up the corresponding IP address of the domain name in its

DNS database. If no match is found, it sends a query to a higher DNS server. This

process continues until a result, whether success or failure, is returned.

4 The DNS client returns the resolution result to the application after receiving a

response from the DNS server.