3Com Switch 4210 9-Port, Configuration Manual

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DNS C
ONFIGURATION
n
This chapter covers only IPv4 DNS configuration. For details about IPv6 DNS, refer
to “IPv6 Mangement Configuration” on page 525.
DNS Overview
Domain name system (DNS) is a mechanism used for TCP/IP applications to provide
domain name-to-IP address translation. With DNS, you can use memorizable and
meaningful domain names in some applications and let the DNS server resolve it
into correct IP addresses.
There are two types of DNS services, static and dynamic. Each time the DNS server
receives a name query, it checks its static DNS database before looking up the
dynamic DNS database. Reduction of the searching time in the dynamic DNS
database would increase efficiency. Some frequently used addresses can be put in
the static DNS database.
n
Currently, when acting as a DNS client, the Switch 4210 supports both static and
dynamic DNS clients.
Static Domain Name
Resolution
The static domain name resolution means manually setting up mappings between
domain names and IP addresses. IP addresses of the corresponding domain names
can be found in the static domain name resolution table for applications, such as
Telnet.
Dynamic Domain Name
Resolution
Resolution 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 in 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 the query to the
DNS server.
3 The DNS server looks up its DNS database for a match. If no match is found, it
sends a query to a higher-level DNS server. This process continues until a result,
success or failure, is returned.
4 The DNS client performs the next operation according to the result.