DNS fundamentals

This section provides conceptual material on the Domain Name Service (DNS) implementation for the switch. Review this content before you make changes to the configurable DNS options.

DNS client

Every equipment interface connected to a Transmission Control Protocol over IP (TCP/IP) network is identified with a unique IPv4 or IPv6 address. You can assign a name to every machine that uses an IPv4 or IPv6 address. The TCP/IP does not require the usage of names, but these names make the task easier for network managers in the following ways:

To establish the mapping between an IP name and an IPv4 or an IPv6 address you use the Domain Name Service (DNS). DNS is a hierarchical database that you can distribute on several servers for backup and load sharing. After you add a new hostname, update this database. The information is sent to all the different hosts. An IP client that resolves the mapping between the hostname and the IP address sends a request to one of the database servers to resolve the name.

After you establish the mapping of IP name and IP address, the application is modified to use a hostname instead of an IP address. The switch converts the hostname to an IP address.

If the entry to translate the hostname to IP address is not in the host file, the switch queries the configured DNS server for the mapping from hostname to IP address. You can configure connections for up to three different DNS servers—primary, secondary and tertiary. First the primary server is queried, and then the secondary, and finally the tertiary.

The DNS client tracks any server addresses or domain names provided from a DHCP server. If a DHCP server provides info to the DNS client, the DNS configuration is classified as dynamic. You can manually delete dynamic DNS entries, but cannot manually add dynamic DNS entries. You can view the Dynamic DNS entries with show ip dns or show sys dns. Dynamic DNS entries are not saved in the configuration file. The status monitoring of DNS occurs every 60 seconds.

DNS modifies Ping, Telnet, and copy applications. You can enter a hostname or an IP address to invoke Ping, Telnet, and copy applications.

A log/debug report is generated for all the DNS requests sent to DNS servers and all successful DNS responses received from the DNS servers.

IPv6 Support

The Domain Name Service (DNS) used by the switch supports both IPv4 and IPv6 addresses with no difference in functionality or configuration.