Table Of Contents

Configuring DNS

Understanding How DNS Works

Default DNS Configuration

Configuring DNS

Setting Up and Enabling DNS

Clearing a DNS Server

Clearing the DNS Domain Name

Disabling DNS

Configuring DNS

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This chapter describes how to configure the Domain Name System (DNS) on the Catalyst enterprise LAN switches.

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Note For complete syntax and usage information for the commands used in this chapter, refer to the Command Reference—Catalyst 4000 Family, Catalyst 2948G, and Catalyst 2980G Switches.

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This chapter consists of these major sections:

•Understanding How DNS Works

•Default DNS Configuration

•Configuring DNS

Understanding How DNS Works

DNS is a distributed database with which you can map host names to IP addresses through the DNS protocol from a DNS server. When you configure DNS on the switch, you can substitute the host name for the IP address with all IP commands, such as ping, telnet, upload, and download.

To use DNS, you must have a DNS name server on your network.

You can specify a primary DNS name server on the switch as well as two backup servers. The first server specified is the primary unless you explicitly identify the primary server. The switch sends DNS queries to the primary server first. If the query to the primary server fails, the backup servers are queried.

Default DNS Configuration

Table 35-1 shows the default DNS configuration.

Table 35-1 Default DNS Configuration  

Feature	Default Value
DNS enable state	Disabled
DNS default domain name	Null
DNS servers	None specified

Configuring DNS

The following sections describe how to configure DNS:

•Setting Up and Enabling DNS

•Clearing a DNS Server

•Clearing the DNS Domain Name

•Disabling DNS

Setting Up and Enabling DNS

To set up and enable DNS on the switch, perform this task in privileged mode:

	Task	Command
Step 1	Specify the IP address of one or more DNS servers.	set ip dns server ip_addr [primary]
Step 2	Set the domain name.	set ip dns domain name
Step 3	Enable DNS.	set ip dns enable
Step 4	Verify the DNS configuration.	show ip dns [noalias]

This example shows how to set up and enable DNS on the switch and verify the configuration:

Console> (enable) set ip dns server 10.2.2.1

10.2.2.1 added to DNS server table as primary server.

Console> (enable) set ip dns server 10.2.24.54 primary

10.2.24.54 added to DNS server table as primary server.

Console> (enable) set ip dns server 10.12.12.24

10.12.12.24 added to DNS server table as backup server.

Console> (enable) set ip dns domain corp.com

Default DNS domain name set to corp.com

Console> (enable) set ip dns enable

DNS is enabled

Console> (enable) show ip dns

DNS is currently enabled.

The default DNS domain name is: corp.com

DNS name server                            status

----------------------------------------   -------

dns_serv2

dns_serv1                                  primary

dns_serv3

Console> (enable)

Clearing a DNS Server

To clear DNS servers from the DNS server table, perform this task in privileged mode:

	Task	Command
Step 1	Remove one or all of the DNS servers from the table.	clear ip dns server [ip_addr | all]
Step 2	Verify the DNS configuration.	show ip dns [noalias]

This example shows how to clear a DNS server from the DNS server table:

Console> (enable) clear ip dns server 10.12.12.24

10.12.12.24 cleared from DNS table

Console> (enable)

This example shows how to clear all of the DNS servers from the DNS server table:

Console> (enable) clear ip dns server all

All DNS servers cleared

Console> (enable)

Clearing the DNS Domain Name

To clear the default DNS domain name, perform this task in privileged mode:

	Task	Command
Step 1	Clear the default DNS domain name.	clear ip dns domain
Step 2	Verify the DNS configuration.	show ip dns [noalias]

This example shows how to clear the default DNS domain name:

Console> (enable) clear ip dns domain

Default DNS domain name cleared.

Console> (enable)

Disabling DNS

To disable DNS, perform this task in privileged mode:

	Task	Command
Step 1	Disable DNS on the switch.	set ip dns disable
Step 2	Verify the DNS configuration.	show ip dns [noalias]

This example shows how to disable DNS on the switch:

Console> (enable) set ip dns disable

DNS is disabled

Console> (enable)