Dns Proxy Configuration; Introduction To Dns Proxy; Operational Mechanism Of Dns Proxy - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
# Configure a static route to the DNS server.
[Router] ip route-static 10.110.66.66 s0
3.3.5 Troubleshooting
Symptom: Domain name resolving failed.
Solution:
1) Check the software, making sure that:
IP address of the domain name server is correctly configured.
The device and the domain name server have routes between them.
DNS resolving is enabled.
2) Check the hardware, making sure the network connection cable is in good
condition and securely connected.

3.4 DNS Proxy Configuration

3.4.1 Introduction to DNS Proxy

DNS proxy is enabled on the router functioning as the gateway proxy for a LAN. It
allows clients on the LAN to contact an external DNS server for service when accessing
the Internet in case no internal DNS server is present.

3.4.2 Operational Mechanism of DNS Proxy

The following describes how DNS proxy operates:
1) The DNS client sends a DNS request to the DNS proxy, using the IP address of
the DNS proxy as the destination address.
2) When the DNS proxy receives the request, it replaces the destination address with
the IP address of a DNS server, and then forwards the request to the DNS server.
When multiple DNS server addresses are available, the DNS proxy sends the
request to the one configured first. If no response is received, the DNS client
resends the request and the DNS proxy forwards this resent request to the second
DNS server. This process continues until a response is received from a DNS
server.
3) The DNS server sends a response back to the DNS proxy.
4) The DNS proxy replaces the source IP address in the received response with the
its own IP address and forwards the response to the DNS client.
Now, the DNS client can use the IP address carried in the received response to access
the Internet.
3Com Corporation
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Chapter 3 DNS Configuration