Configuring DNS
This chapter describes how to configure the Domain Name Server (DNS) client on the Cisco NX-OS device.
About DNS Clients
This section includes the following topics:
DNS Client Overview
If your network devices require connectivity with devices in networks for which you do not control the 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, which 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 hostname 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 the 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 hostname in this domain, the File Transfer Protocol (FTP) system, for example, is identified as ftp.cisco.com.
Name Servers
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 identify the hostnames, 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.
DNS Operation
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 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 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.
High Availability
Cisco NX-OS supports stateless restarts for the DNS client. After a reboot or supervisor switchover, Cisco NX-OS applies the running configuration.
Virtualization Support
Cisco NX-OS supports multiple instances of the DNS clients that run on the same system. You can configure a DNS client. You can optionally have a different DNS client configuration in each virtual routing and forwarding (VRF) instance.
Licensing Requirements for DNS Clients
The following table shows the licensing requirements for this feature:
Prerequisites for DNS Clients
Guidelines and Limitations for DNS
The DNS client has the following configuration guidelines and limitations:
Default Settings
Table 4-1 lists the default settings for DNS client parameters.
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Configuring DNS Clients
This section 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.
Configuring the DNS Client
You can configure the DNS client to use a DNS server on your network.
BEFORE YOU BEGIN
SUMMARY STEPS
2. ip host name address1 [ address2... address6 ]
3. (Optional) ip domain-name name [ use-vrf vrf-name ]
4. (Optional) ip domain-list name [ use-vrf vrf-name ]
5. (Optional) ip name-server address1 [ address2... address6 ] [ use-vrf vrf-name ]
DETAILED STEPS
This example shows how to configure a default domain name and enable DNS lookup:
switch(config)# ip domain-name cisco.com
switch(config)# ip name-server 192.0.2.1 use-vrf management
switch(config)# ip domain-lookup
switch(config)# copy running-config startup-config
Configuring Virtualization
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.
BEFORE YOU BEGIN
SUMMARY STEPS
3. (Optional) ip domain-name name [ use-vrf vrf-name ]
4. (Optional) ip domain-list name [ use-vrf vrf-name ]
5. (Optional) ip name-server server-address1 [ server-address2... server-address6 ] [ use-vrf vrf-name ]
DETAILED STEPS
This example shows how to configure a default domain name and enable DNS lookup within a VRF:
switch(config)# vrf context Red
switch(config-vrf)# ip domain-name cisco.com
switch(config-vrf)# ip name-server 192.0.2.1 use-vrf management
switch(config-vrf)# copy running-config startup-config
Verifying the DNS Client Configuration
To display the DNS client configuration, perform one of the following tasks:
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Configuration Examples for the DNS Client
This example shows how to establish a domain list with several alternate domain names:
This example shows how to configure the hostname-to-address mapping process and specify IP DNS-based translation. The example also configures the addresses of the name servers and the default domain name.
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