User guide

DHCP Relay Command Reference Domain name system - DNS
5-83
iMG/RG Software Reference Manual (System Administration)
Description This command updates the DHCP relay configuration. Changes made to the relay config-
uration will not take effect until this command has been entered.
Example --> dhcprelay update
dhcprelay: Reset request acknowledged. Reset imminent.
5.2 Domain name system - DNS
DNS is an abbreviation for Domain Name System, a system for naming computers and network services that is
organized into a hierarchy of domains. DNS naming is used in TCP/IP networks, such as the Internet, to locate
computers and services through user-friendly names. When a user enters a DNS name in an application, DNS
services can resolve the name to other information associated with the name, such as an IP address.
For example, most users prefer a friendly name such as alliedtelesyn.com to locate a computer such as a mail or
Web server on a network. A friendly name can be easier to learn and remember. However, computers commu-
nicate over a network by using numeric addresses. To make use of network resources easier, name services
such as DNS provide a way to map the user-friendly name for a computer or service to its numeric address. If
you have ever used a Web browser, you have used DNS.
The following graphic shows a basic use of DNS, which is finding the IP address of a computer based on its
name.
FIGURE 5-1 Domain Name System
In this example, a client computer queries a server, asking for the IP address of a computer configured to use
host.alliedtelesyn.com as its DNS domain name. Because the server is able to answer the query based on its
local database, it replies with an answer containing the requested information, which is a host (A) resource
record that contains the IP address information for host.alliedtelesyn.com. The example shows a simple DNS
query between a single client and server. In practice, DNS queries can be more involved than this and include
additional steps not shown here.
DNS Client DNS Server
What is IP address for host.alliedtelesis.com?
host.alliedtelesis.com = 192.168.1.20
DNS Server Data
host.alliedtelesis.com 192.168.1.20