H3C Technologies H3C S7500E Series Switches - Manual (Page 93)

9-3
DNS Proxy
Introduction to DNS proxy
A DNS proxy forwards DNS requests and replies between DNS clients and a DNS server.
As shown in Figure 9-2 , a DNS client sends a DNS request to the DNS proxy, which forwards the
request to the designated DNS server, and conveys the reply from the DNS server to the client.
The DNS proxy simplifies network management. When the DNS server address is changed, you only
need to change the configuration on the DNS proxy instead of on each DNS client.
Figure 9-2 DNS proxy networking application
Operation of a DNS proxy
1) A DNS client considers the DNS proxy as the DNS server, and sends a DNS request to the DNS
proxy, that is, the destination address of the request is the IP address of the DNS proxy.
2) The DNS proxy searches the local static domain name resolution table and dynamic domain name
resolution table after receiving the request. If the requested information is found, the DNS proxy
returns a DNS reply to the client.
3) If the requested information is not found, the DNS proxy sends the request to the designated DNS
server for domain name resolution.
4) After receiving a reply from the DNS server, the DNS proxy records the IP address-to-domain
name mapping and forwards the reply to the DNS client.
With no DNS server or route to a DNS server specified, the DNS proxy does not forward DNS requests,
or answer the requests from the DNS clients.