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This chapter describes how to configure the Domain Name Server (DNS) client.
This chapter includes the following sections:
•Information About DNS Clients
•Licensing Requirements for DNS Clients
•Prerequisites for DNS Clients
•Configuration Guidelines and Limitations
•Verifying the DNS Client Configuration
•DNS Client Example Configuration
•DNS Client Example Configuration
This section includes the following topics:
If your network devices require connectivity with devices in networks for which you do not control name assignment, you can assign device names that uniquely identify your devices within the entire internetwork using the domain name server (DNS). DNS uses a hierarchical scheme for establishing host names for network nodes. This allows local control of the segments of the network through a client-server scheme. The DNS system can locate a network device by translating the host name of the device into its associated IP address.
On the Internet, a domain is a portion of the naming hierarchy tree that refers to general groupings of networks based on organization type or geography. Domain names are pieced together with periods (.) as the delimiting characters. For example, Cisco is a commercial organization that the Internet identifies by a com domain, so its domain name is cisco.com. A specific host name in this domain, the File Transfer Protocol (FTP) system, for example, is identified as ftp.cisco.com.
Name servers keep track of domain names and know the parts of the domain tree for which they have complete information. A name server may also store information about other parts of the domain tree. To map domain names to IP addresses in Cisco NX-OS, you must first identify the host names, then specify a name server, and enable the DNS service.
Cisco NX-OS allows you to statically map IP addresses to domain names. You can also configure Cisco NX-OS to use one or more domain name servers to find an IP address for a host name.
A name server handles client-issued queries to the DNS server for locally defined hosts within a particular zone as follows:
•An authoritative name server responds to DNS user queries for a domain name that is under its zone of authority by using the permanent and cached entries in its own host table. If the query is for a domain name that is under its zone of authority but for which it does not have any configuration information, the authoritative name server simply replies that no such information exists.
•A name server that is not configured as the authoritative name server responds to DNS user queries by using information that it has cached from previously received query responses. If no router is configured as the authoritative name server for a zone, queries to the DNS server for locally defined hosts will receive nonauthoritative responses.
Name servers answer DNS queries (forward incoming DNS queries or resolve internally generated DNS queries) according to the forwarding and lookup parameters configured for the specific domain.
Cisco NX-OS supports stateless restarts for the DNS client. After a reboot or supervisor switchover, Cisco NX-OS applies the running configuration.
Cisco NX-OS supports multiple instances of the DNS clients that run on the same system. You can configure a DNS client in each VDC.You can optionally have a different DNS client configuration in each VRF within a VDC. By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF. See the Cisco NX-OS Virtual Device Context Configuration Guide and Chapter 14, "Configuring Layer 3 Virtualization."
The following table shows the licensing requirements for this feature:
The DNS client has the following prerequisites:
•You must have a DNS name server on your network.
•If you configure VDCs, install the Advanced Services license and enter the desired VDC (see to the Cisco NX-OS Virtual Device Context Configuration Guide).
You configure the DNS client in a specific VRF. If you do not specify a VRF, Cisco NX-OS uses the default VRF.
This section describes how to configure DNS clients and includes the following topics:
Note If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.
You can configure the DNS client to use a DNS server on your network.
Ensure that you have a domain name server on your network.
Ensure that you are in the correct VDC (or use the switchto vdc command).
1. config t
2. ip host name address1 [address2... address6]
3. ip domain-name name [use-vrf vrf-name]
4. ip domain-list name [use-vrf vrf-name]
5. ip name-server server-address1 [server-address2... server-address6] [use-vrf vrf-name]
6. ip domain lookup
7. show hosts
8. copy running-config startup-config
The following example shows how to configure a default domain name and enable DNS lookup:
switch# config t
switch(config)# ip domain-name cisco.com 192.0.2.1 use-vrf management
switch(config)# ip domain-lookup
switch(config# copy running-config startup-config
You can configure a DNS client within a VRF. If you do not enter vrf configuration mode, your DNS client configuration applies to the default VRF.
You can optionally configure a DNS client to use a specified VRF other than the VRF under which you configured the DNS client as a backup VRF. For example, you can configure a DNS client in the Red VRF but use the Blue VRF to communicate with the DNS server if the server cannot be reached through the Red VRF.
Ensure that you have a domain name server on your network.
Ensure that you are in the correct VDC (or use the switchto vdc command).
9. config t
10. vrf context vrf-name
11. ip domain-name name [ se-vrf vrf-name]
12. ip domain-list name [use-vrf vrf-name]
13. ip name-server server-address1 [server-address2... server-address6] [use-vrf vrf-name]
14. ip domain lookup
15. show hosts
16. copy running-config startup-config
The following example shows how to configure a default domain name and enable DNS lookup within a VRF:
switch# config t
switch(config)# vrf context Red
switch(config-vrf)# ip domain-name cisco.com 192.0.2.1 use-vrf management
switch(config-vrf)# ip domain-lookup
switch(config-vrf)# copy running-config startup-config
To verify the DNS client configuration, use the following commands:
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show hosts |
Displays information about DNS. |
This example establishes a domain list with several alternate domain names:
ip domain list csi.com
ip domain list telecomprog.edu
ip domain list merit.edu
This example configures the host name-to-address mapping process and specifies IP DNS-based translation, The example also configures the addresses of the name servers and the default domain name.
ip domain lookup
ip name-server 192.168.1.111 192.168.1.2
ip domain name cisco.com
Table 4-1 lists the default settings for DNS Client parameters.
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DNS client |
Enabled |
For additional information related to implementing DNS Client, see the following sections:
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
— |
Table 4-2 lists the release history for this feature.
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|
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DNS |
4.0(1) |
This feature was introduced. |