Your software release might not support all the features documented in this module. For the latest caveats and feature information,
see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notes for your software release. To find information about the features documented in this module, and to
see a list of the releases in which each feature is supported, see the "New and Changed Information"chapter or the Feature
History table in this chapter.
Information About DNS Clients
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.
DNS 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.
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
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 for DNS Clients
Cisco NX-OS supports stateless restarts for the DNS client. After a reboot or supervisor switchover, Cisco NX-OS applies the
Virtualization Support for DNS Clients
Cisco NX-OS supports multiple instances of the DNS clients that run on the same system. You can configure a DNS client in
each virtual device connect (VDC).You can optionally have a different DNS client configuration in each virtual routing and
forwarding (VRF) instance 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 .
Prerequisites for DNS Clients
You must have a DNS name server on your network.
Guidelines and Limitations for DNS Clients
You configure the DNS client in a specific VRF. If you do not specify a VRF, Cisco NX-OS uses the default VRF.
Cisco NX-OS does not support underscore in a DNS name. Hence do not use underscore in a DNS name.
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.
Default Settings for DNS Client Parameters
The table below lists the default settings for DNS client parameters.
Table 1. Default DNS Client Parameters
Configuring DNS Clients
Configuring the DNS
Before you begin
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).
Command or Action
address1 [address2... address6]
Defines up to
six static hostname-to-address mappings in the hostname cache. The address can
be either an IPv4 address or an IPv6 address.
default domain name that Cisco NX-OS uses to complete unqualified host names.
You can optionally define a VRF that Cisco NX-OS uses to resolve this domain
name if it cannot be resolved in the VRF that you configured this domain name
appends the default domain name to any hostname that does not contain a
complete domain name before starting a domain-name lookup.
use-vrf is used as a DNS query supposed to be sending on a
different VRF and listening for the reply on a different VRF. Example: DNS
query is sent over VRF RED while the response should come on VRF Default.
ip dns source-interface
[loopback Xdifferent interface]
Defines what will be the source IP for the DNS Query which will
be sent out. When DNS server tries to answer back, it will use the Loopback0 as
the destination and there should be a valid return route.
additional domain names that Cisco NX-OS can use to complete unqualified
hostnames. You can optionally define a VRF that Cisco NX-OS uses to resolve
these domain names if they cannot be resolved in the VRF that you configured
this domain name under.
Cisco NX-OS uses
each entry in the domain list to append that domain name to any hostname that
does not contain a complete domain name before starting a domain-name lookup.
Cisco NX-OS continues this process for each entry in the domain list until it
finds a match.
name-serveraddress1 [address2... address6] [
Defines up to
six name servers. The address can be either an IPv4 address or an IPv6 address.
optionally define a VRF that Cisco NX-OS uses to reach this name server if it
cannot be reached in the VRF that you configured this name server under.
DNS-based address translation. This feature is enabled by default.
Saves the change
persistently through reboots and restarts by copying the running configuration
to the startup configuration.
Verifying the DNS Client Configuration
To display the DNS client configuration, perform the following task:
Displays information about DNS.
Configuration Examples for DNS Clients
This example shows how to establish 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 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.
ip domain lookup
ip name-server 192.168.1.111 192.168.1.2
ip domain name cisco.com
Related Documents for DNS Clients
DNS Client CLI commands
Cisco Nexus 7000 Series NX-OS Unicast Routing Command Reference