4.1 DNS Overview
This section describes the DNS concept.
TCP/IP defines IP addresses to locate devices. It is difficult to remember the IP address of a
device; therefore, host names are designed in the form of strings. These host names are in one-
to-one mapping with IP addresses. Therefore, DNS is developed to provide a translation and
query mechanism between IP addresses and host names.
The DNS is a hierarchical naming system that designates meaningful names for devices on the
network and sets a DNS server to associate domain names with IP addresses. In this manner,
you can use the simple and meaningful domain names instead of the complicated IP addresses.
4.2 DNS Features Supported by the AR150/200
The AR150/200 can function as the DNS client, DNS proxy/relay, or dynamic DNS (DDNS)
client.
AR150/200 Functioning as a DNS Client
The AR150/200 can be used as a DNS Client. A DNS client provides the following functions:
l
Static DNS resolution. Mappings between domain names and IP addresses are configured
manually. When a DNS client requests the IP address mapping a domain name, it searches
for the specified domain name in the static DNS table to obtain the mapping IP address.
l
Dynamic DNS resolution. A DNS server searches for the IP address mapping a domain
name. When the DNS server receives a query message from a DNS client, it searches for
the IP address mapping the domain name in its DNS database. If no matching entry is found,
it sends a query message to an upper-level DNS server. This process continues until the
DNS server finds the corresponding IP address or detecting that the domain name does not
exist. The DNS server then sends a response to the DNS client.
AR150/200 Functioning as a DNS Proxy/Relay
The AR150/200 supports the DNS Proxy/Relay function. If no DNS server is deployed on a
LAN, a DNS client on the LAN can connect to an external DNS server through the
AR150/200 enabled with DNS proxy or relay. After the external DNS server translates the
domain name of the DNS client to an IP address, the DNS client can access the Internet.
DNS relay is similar to DNS proxy. The difference is that the DNS proxy searches for DNS
entries saved in the local cache after receiving DNS query messages from DNS clients. The DNS
relay, however, directly forwards DNS query messages to the DNS server, reducing the
workload.
AR150/200 Functioning as a DDNS Client
The AR150/200 can function as the DDNS client. After a Layer 3 interface or a VLANIF
interface of the AR150/200 is configured as a DDNS client, the AR150/200 notifies the DDNS
server about the new IP address when the IP address of the interface enabled with DDNS client
changes. The DDNS server dynamically updates the mapping between the domain name and
the IP address on the DNS server to ensure that the IP address can be resolved correctly.
Huawei AR150&200 Series Enterprise Routers
Configuration Guide - IP Service
4 DNS Configuration
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
83
