DNS Server Support for NS Records
This feature module describes the DNS Server Support for NS Records feature and includes the following sections:
•Finding Feature Information
•Supported Standards, MIBs, and RFCs
•Command Reference, page 4
Domain Name System (DNS) is a client/server mechanism used to access a distributed database. The server portion of the DNS client/server mechanism is the name server (NS). An NS can be responsible for presenting information about a portion of the DNS distributed database or can be a forwarding/caching NS. In the latter case, the NS queries other NSs rather than maintaining a local portion of the DNS database.
DistributedDirector has improved server load-balancing capacity with the DNS Server Support for NS Records feature. This feature adds support for NS records to the Cisco IOS DNS server. With this feature, the DistributedDirector can distribute the server-selection process to multiple DistributedDirectors, improving overall server capacity.
This feature allows an NS to delegate server responsibility for a domain by returning an NS record when queried. This function is useful to DistributedDirector because a computationally load can be distributed over a large number of DistributedDirectors, so each DistributedDirector can be free to perform computational expensive actions to select the best server.
For more information on the Cisco DistributedDirector, see the following documents, which are located on Cisco.com at http://www.cisco.com/univercd/cc/td/doc/product/iaabu/distrdir/index.htm:
•Cisco DistributedDirector 4700-M Installation and Configuration Guide
•Release Notes for Cisco DistributedDirector System Software
•Cisco DistributedDirector Enhancements for Release 11.1(18)IA
•Cisco DistributedDirector Enhancements for Release 11.1(25)IA
•Cisco DistributedDirector Enhancements for Release 11.1(28)IA
•Cisco DistributedDirector Enhancements for Release 12.1(5)T
•Dynamic Feedback Protocol Support in DistributedDirector
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Supported Standards, MIBs, and RFCs
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
DNS is defined in RFC 1035.
See the following sections for configuration tasks for this feature. Each task in the list is identified as either required or optional.
•Configuring DNS Server Support for NS Records (required)
•Verifying DNS Server Support for NS Records (optional)
Configuring DNS Server Support for NS Records
To configure the DistributedDirector to create an NS resource record to be returned when the DNS server is queried for the associated domain, use the following commands in global configuration mode:
Router(config)# ip host www.xyz.com ns ns.xyz.com
Configures the DistributedDirector to create an NS resource record to be returned when the DNS server is queried for the associated domain.
Router(config)# ip host ns.xyz.com 10.0.0.1 10.0.0.2 10.0.0.3
Defines a static host-name-to-address mapping in the host cache.
ip director host ns.xyz.com priority random 1
Configures the order in which the DistributedDirector considers metrics when picking a server.
Router(config)# ip dns primary xyz.com soa ns.xyz.com
Identifies the DistributedDirector as the primary DNS NS for a domain and as the SOA record source.
Verifying DNS Server Support for NS Records
To verify that the DistributedDirector is configured with NS record support, use the show running-config command or the show host command.
This section provides the following configuration example:
•DNS Server Support for NS Records Example
DNS Server Support for NS Records Example
The following example shows a top-level DistributedDirector using a low-cost metric, such as portion or random, to distribute load over second-level DistributedDirectors. Second-level DistributedDirectors then use more expensive metrics, such as drp-ext or drp-rtt, to perform more precise server selection. The relevant portions of this configuration are show below:
ip host www.xyz.com ns ns.xyz.com
ip host ns2.xyz.com 10.0.0.1 10.0.0.2 10.0.0.3
ip director host ns.xyz.com priority random 1
ip dns primary www.xyz.com soa ns2.xyz.com
ip host www.xyz.com 10.0.0.4 10.0.0.5 10.0.0.6
ip director host www.xyz.com priority drp-ext 1
ip director host www.xyz.com priority drp-rtt 2
ip director server 10.0.0.4 drp-association 10.0.0.7
ip director server 10.0.0.5 drp-association 10.0.0.8
ip director server 10.0.0.6 drp-association 10.0.0.9
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
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