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Table Of Contents
DNS Server Support for NS Records
Supported Standards, MIBs, and RFCs
Configuring DNS Server Support for NS Records
Verifying DNS Server Support for NS Records
DNS Server Support for NS Records Example
DNS Server Support for NS Records
This feature module describes the DNS Server Support for NS Records feature and includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
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.
Benefits
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.
Related Documents
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:
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Supported Platforms
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Supported Standards, MIBs, and RFCs
Standards
None
MIBs
None
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:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
RFCs
DNS is defined in RFC 1035.
Configuration Tasks
See the following sections for configuration tasks for this feature. Each task in the list is identified as either required or optional.
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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:
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.
Configuration Examples
This section provides the following configuration example:
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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:
Top-Level DistributedDirector
ip host www.xyz.com ns ns.xyz.comip host ns2.xyz.com 10.0.0.1 10.0.0.2 10.0.0.3ip director host ns.xyz.com priority random 1ip dns primary www.xyz.com soa ns2.xyz.comSecond-Level DistributedDirector
ip host www.xyz.com 10.0.0.4 10.0.0.5 10.0.0.6ip director host www.xyz.com priority drp-ext 1ip director host www.xyz.com priority drp-rtt 2ip director server 10.0.0.4 drp-association 10.0.0.7ip director server 10.0.0.5 drp-association 10.0.0.8ip director server 10.0.0.6 drp-association 10.0.0.9Command Reference
This section documents new commands. All other commands used with the DistributedDirector are documented in the "Command Summary" and "Reference" sections of the Cisco DistributedDirector installation and configuration guides.
ip host ns
To configure the DistributedDirector to create a name server (NS) resource record to be returned when the Domain Name System (DNS) server is queried for the associated domain, use the ip host ns command in global configuration mode. To remove the NS records, use the no form of this command.
ip host domain-name ns server-name
no ip host domain-name ns server-name
Syntax Description
domain-name
Name for which authority is delegated to another NS such as a second-level DistributedDirector.
server-name
Name of the second-level DNS server.
Defaults
None
Command Modes
Global configuration
Command History
Usage Guidelines
The ip host ns command allows the DistributedDirector to distribute the server selection process to multiple DistributedDirectors, providing greater scalability and better administrative control.
A DNS server can delegate responsibility for a domain to another DNS server by returning an NS record when queried. This task is especially useful to DistributedDirector because in some cases the work required to determine the best DNS reply cannot be computed fast enough. Instead, DistributedDirector can return an NS record, delegating the authority for the requested data to one or more second-level DistributedDirectors.
Examples
The following example shows a top-level DistributedDirector that uses 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 shown below.
Top-Level DistributedDirector
ip host www.xyz.com ns ns.xyz.comip host ns2.xyz.com 10.0.0.1 10.0.0.2 10.0.0.3ip director host ns.xyz.com priority random 1ip dns primary www.xyz.com soa ns2.xyz.comSecond-Level DistributedDirector
ip host www.xyz.com 10.0.0.4 10.0.0.5 10.0.0.6ip director host www.xyz.com priority drp-ext 1ip director host www.xyz.com priority drp-rtt 2ip director server 10.0.0.4 drp-association 10.0.0.7ip director server 10.0.0.5 drp-association 10.0.0.8ip director server 10.0.0.6 drp-association 10.0.0.9