Foundry NetIron M2404C and M2404F Metro Access Switches
Switch Administration (Rev. 03)
Domain Name System (DNS) Resolver © 2008 Foundry Networks, Inc.
Page 76 of 87
Domain Name System (DNS) Resolver
The Domain Name System (DNS) is the means by which Internet domain names are located and
translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember
“handle” for an Internet address.
Overview
You can define up to three DNS servers. If a query to the primary address fails to be resolved after
three attempts, the next gateway address is queried. This process continues for each defined
gateway address until the query is resolved
or when all the queries have failed. The order in which
the default gateway addresses are polled is the same as the order in which the user enters them.
DNS is a distributed database with which the user can map host names to IP addresses through the
DNS protocol from a DNS server. When the user configures DNS, the user can substitute the host
name for the IP address with the
ping
and
traceroute
commands in Privileged (Enable) mode.
The application software supports a cache mechanism for names that are already resolved. If a
resolve query arrives at the device, the DNS Resolver first searches the requested name in that
cache. If it does not find any match, the DNS Resolver delivers the query to the DNS server. The
TTLs (time to live) of those cache entries are extracted from the Resource Record (RR) of the
server response.
To use DNS, the user must have a DNS name server present on the network.
DNS Resolver Default Configuration
Table 30
shows the DNS Resolver default configuration.
Table 30: DNS Resolver Default Configuration
Parameter
Default Value
DNS servers
None specified
Configuring and Displaying DNS Resolver
Table 31
lists the DNS Resolver commands.
Table 31: DNS Resolver Commands
Command
Description
ip dns server
Specifies the IP address of one or more DNS servers.
show ip dns
Displays the current configuration of the DNS Resolver.
Setting DNS Server
The
ip dns server
command, in Global Configuration mode, specifies the IP address of one or
more DNS servers. Up to three DNS servers can be added.