3Com Switch 7754, Configuration Manual, Page: 831 / 940

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DNS C
ONFIGURATION
DNS Overview
Domain name system (DNS) is a distributed database system that provides domain
name-to-IP address mappings for TCP/IP applications. With DNS, users using IP
applications can directly use meaningful easy-to-remember domain names, which
will be resolved and mapped to corresponding IP addresses by DNS servers.
There are two types of DNS resolution, “Static DNS Resolution” on page 831 and
“Dynamic DNS Resolution” on page 831. When a name query is received, the
static resolution is first performed to check the static DNS list. If the static
resolution fails, the dynamic resolution is performed. Because dynamic resolution
needs the participating of DNS server and may spend some time, you can put
some commonly used domain names in the static DNS list to increase the
resolution efficiency.
Static DNS Resolution With static DNS resolution, you can manually configure some name-to-address
mappings in the static DNS list, and the system will search the static list for
corresponding IP addresses when users use domain names with some applications
(such as telnet).
Dynamic DNS Resolution Resolving procedure
The procedure of dynamic DNS resolution 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 DNS cache for a match. If a match is found, it
returns the corresponding IP address to the user program. If not, it sends a query
to the DNS Server.
3 The DNS Server looks up its database for a match. If no match is found, it sends a
query to its parent DNS Server. If the parent DNS Server does not have the
information, it sends the query to another server. This process continues until a
result (either successful or failed) is found. Finally, the resolution result is returned
to the DNS Client.
4 The DNS Client performs the next operation according to the result.