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DNS CONFIGURATION
When configuring DNS, go to these sections for information you are interested in:
■ “DNS Overview” on page 971
■ “Configuring the DNS Client” on page 973
■ “Configuring the DNS Proxy” on page 974
■ “Displaying and Maintaining DNS” on page 974
■ “DNS Configuration Examples” on page 975
■ “Troubleshooting DNS Configuration” on page 980
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This document only covers IPv4 DNS configurations. For introduction to IPv6 DNS
configurations, refer to “Configuring IPv6 DNS” on page 515.
DNS Overview Domain Name System (DNS) is a distributed database used by TCP/IP applications
to translate domain names into corresponding IP addresses. With DNS, you can
use easy-to-remember domain names in some applications and let the DNS server
translate them into correct IP addresses.
There are two types of DNS services, static and dynamic. After a user specifies a
name, the device checks the local static name resolution table for an IP address. If
no IP address is available, it contacts the DNS server for dynamic name resolution,
which takes more time than static name resolution. Therefore, some frequently
queried name-to-IP address mappings are stored in the local static name resolution
table to improve efficiency.
Static Domain Name
Resolution
The static domain name resolution means setting up mappings between domain
names and IP addresses. IP addresses of the corresponding domain names can be
found in the static domain resolution table when you use applications such as
telnet.
Dynamic Domain Name
Resolution
Resolving procedure
Dynamic domain name resolution is implemented by querying the DNS server. The
resolution procedure is as follows:
1 A user program sends a name query to the resolver of the DNS client.
2 The DNS resolver looks up the local domain name cache for a match. If a match is
found, it sends the corresponding IP address back. If not, it sends a query to the
DNS server.
3 The DNS server looks up the corresponding IP address of the domain name in its
DNS database. If no match is found, it sends a query to a higher level DNS server.
This process continues until a result, whether successful or not, is returned.
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