Information About DNS Clients
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.
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
• A name server that is not configured as the authoritative name server responds to DNS user queries by
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 running configuration.
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 6.x
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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.
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.
Configuring DNS
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