Configuring DNS

Contents

1Overview

2

Configuration and Operations Tasks
2.1Configure DNS
2.2Enable DNS to Establish Subscriber Sessions (Optional)
2.3Configure Static Hostname-to-IP Address Mappings (Optional)
2.4Operations Tasks

3

Configuration Examples
Copyright

© Ericsson AB 2009–2011. All rights reserved. No part of this document may be reproduced in any form without the written permission of the copyright owner.

Disclaimer

The contents of this document are subject to revision without notice due to continued progress in methodology, design and manufacturing. Ericsson shall have no liability for any error or damage of any kind resulting from the use of this document.

Trademark List
SmartEdge is a registered trademark of Telefonaktiebolaget LM Ericsson.

1   Overview

This document provides an overview of the Domain Name System (DNS) features supported by the SmartEdge® router and describes the tasks used to configure, monitor, and administer DNS. It also provides DNS configuration examples.

Note:  
When IP Version 6 (IPv6) addresses are not referenced or explicitly specified, the term, IP address, can refer generally to IP Version 4 (IPv4) addresses, IPv6 addresses, or IP addressing. In instances where IPv6 addresses are referenced or explicitly specified, the term, IP address, refers only to IPv4 addresses. For a description of IPv6 addressing and the types of IPv6 addresses, see RFC 3513, Internet Protocol Version 6 (IPv6) Addressing Architecture.

DNS maps hostnames to IP addresses. When a command refers to a hostname, the OS of the SmartEdge router consults the host table for mappings to IP addresses. If the information is not in the table, the OS generates a DNS query to resolve the hostname. DNS is enabled on a per-context basis, with one domain name allowed per context.

2   Configuration and Operations Tasks

Note:  
In this section, the command syntax in the task tables displays only the root command; for the complete command syntax, see Command List.

To configure DNS, perform the tasks described in the following sections:

2.1   Configure DNS

To configure DNS, perform the tasks described in Table 1; enter all commands in context configuration mode.

Table 1    Configure DNS

Task

Root Command

Notes

Specify a domain name (or alias) for the context.

ip domain-name

You can create up to six domain names per context.

Specify the IP address of a primary (and, optionally, secondary) DNS server with one of the following tasks:

 

For DNS resolution to function, there must be an IP route to the DNS server.

Specify IPv4 addresses.

ip name-servers

 

Specify IPv6 addresses.

ipv6 name-servers

 

Enable theSmartEdge router to use DNS resolution to look up hostname-to-IP address mappings.

ip domain-lookup

For DNS resolution to function, you must configure domain-name lookup.

2.2   Enable DNS to Establish Subscriber Sessions (Optional)

To enable subscriber sessions to be established using DNS, perform the task described in Table 2.

Table 2    Enable DNS to Establish Subscriber Sessions (Optional)

Task

Root Command

Notes

Configure the IP address of a primary or secondary DNS server that a subscriber should use.

dns

Enter this command in subscriber configuration mode.

2.3   Configure Static Hostname-to-IP Address Mappings (Optional)

In addition to having DNS perform dynamic resolution, you can configure static hostname-to-IP address mappings. To do so, perform the task described in Table 3; enter all commands in context configuration mode.

Table 3    Configure Static Hostname-to-IP Address Mappings

Task

Root Command

Notes

Create static hostname-to-IP address mappings in the host table with one of the following tasks:

 

The OS of the SmartEdge router always consults the host table prior to generating a DNS lookup query. You can create up to 64 static entries in the host table.

Create a mapping with an IPv4 address.

ip host (context)

 

Create a mapping with an IPv6 address.

ipv6 host

 

2.4   Operations Tasks

Note:  
In this section, the command syntax in the task tables displays only the root command.

To monitor and troubleshoot DNS features, perform the DNS operations tasks described in Table 4. Enter the debug command in exec mode; enter the show commands in any mode.

Table 4    DNS Operations Tasks

Task

Root Command

Enable the generation of DNS debug messages.

debug ip dns

Display all static hostname-to-IPv4 address mappings stored in the local host table for the current context.

show ip host

Display all static hostname-to-IPv6 address mappings stored in the local host table for the current context.

show ipv6 host

3   Configuration Examples

The following example configures the redback.com domain for the local context and configures a connection to a remote DNS server at IP address, 155.53.130.200. The ip domain-lookup command enables DNS resolution:

[local]Redback(config)#context local 

[local]Redback(config-ctx)#ip domain-lookup 

[local]Redback(config-ctx)#ip domain-name redback.com 

[local]Redback(config-ctx)#ip name-servers 155.53.130.200