3Com Switch 7750 Configuration Guide

DNS CONFIGURATION

DNS Overview Domain name system (DNS) is a distributed database system that provides domain

name-to-IP address mappings for TCP/IP applications. With DNS, users using IP

applications can directly use meaningful easy-to-remember domain names, which

will be resolved and mapped to corresponding IP addresses by DNS servers.

There are two types of DNS resolution, “Static DNS Resolution” on page 831 and

“Dynamic DNS Resolution” on page 831. When a name query is received, the

static resolution is first performed to check the static DNS list. If the static

resolution fails, the dynamic resolution is performed. Because dynamic resolution

needs the participating of DNS server and may spend some time, you can put

some commonly used domain names in the static DNS list to increase the

resolution efficiency.

Static DNS Resolution With static DNS resolution, you can manually configure some name-to-address

mappings in the static DNS list, and the system will search the static list for

corresponding IP addresses when users use domain names with some applications

(such as telnet).

Dynamic DNS Resolution Resolving procedure

The 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, it

returns the corresponding IP address to the user program. If not, it sends a query

to the DNS Server.

3 The DNS Server looks up its database for a match. If no match is found, it sends a

query to its parent DNS Server. If the parent DNS Server does not have the

information, it sends the query to another server. This process continues until a

result (either successful or failed) is found. Finally, the resolution result is returned

to the DNS Client.

4 The DNS Client performs the next operation according to the result.