3Com Switch 7750 Configuration Guide 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” and “Dynamic

DNS Resolution”. 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.