3com 8807 User Guide

Used in the TCP/IP application, Domain Name System (DNS) is a distributed 
database which provides the translation between domain name and the IP 
address. In this way, the user can use domain names that are easy to memorize 
and meaningful, and never needs to keep obscure IP addresses in mind.

There are two kinds of domain name resolutions: static domain name resolution 
and dynamic domain name resolution, which supplement each other in real 
application. On resolving a domain name, use the static resolution first. If it fails, 
use the dynamic resolution method. You can put some common domain names 
into the static domain name resolution table to raise the domain name resolution 
efficiency greatly.

Static domain resolution is to establish maps between domain name and the IP 
address manually. When you perform some applications using domain names, the 
system can obtain the IP address of the specified domain name by searching the 
static domain name resolution table.

Dynamic domain name resolution is implemented by inquiring the domain name 
server. As a DNS client, the switch sends an inquiry request to the domain name 
server, and the domain name server searches the related IP address of the domain 
name in its own database and sends it back to the switch. If the domain name 
server judges that the domain name does not belong to the local domain, it 
forwards the request to the upper level domain name resolution server till the 
resolution is finished.

Dynamic domain name resolution supports the buffer function. It stores each 
successful domain name/IP address mapping that is resolved dynamically in the 
dynamic domain name buffer. When the same domain name is searched next 
time, it can be read directly from the buffer, without requesting the domain name 
server. The aged mapping in the buffer is deleted after a certain period of time to 
ensure the updated contents can be got from the domain name server timely. The 
aging time is set by the domain name server and obtained by the switch from the 
protocol packet.

Dynamic domain name resolution supports the domain name suffix list function. 
You can set some domain name suffixes beforehand and input part of the domain 
name field during the domain name resolution, then the system adds different 
suffixes to the input domain name automatically for resolution. For example, if a 
user wants to search the domain name "3Com.com", he can configure the 
"com" in the suffix list and input "3Com". Then the system connects the input 
domain name with the suffix into "3Com.com" automatically to search. When the 
domain name suffix is used, if the input domain name does not include ".", like