IPv6 Configuration Guide, Cisco IOS Release 15.2M&T
IPv6 Generic Prefix
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IPv6 Generic Prefix

IPv6 Generic Prefix

Last Updated: July 31, 2012

The IPv6 generic prefix feature simplifies network renumbering and allows for automated prefix definition. An IPv6 generic (or general) prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific prefixes (for example, /64) can be defined. When the general prefix is changed, all of the more-specific prefixes based on it will change, too.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Information About IPv6 Generic Prefix

IPv6 General Prefixes

The upper 64 bits of an IPv6 address are composed from a global routing prefix plus a subnet ID, as defined in RFC 3513. A general prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific prefixes (for example, /64) can be defined. When the general prefix is changed, all of the more-specific prefixes based on it will change, too. This function greatly simplifies network renumbering and allows for automated prefix definition.

For example, a general prefix might be 48 bits long ("/48") and the more specific prefixes generated from it might be 64 bits long ("/64"). In the following example, the leftmost 48 bits of all the specific prefixes will be the same, and they are the same as the general prefix itself. The next 16 bits are all different.

 General prefix: 2001:DB8:2222::/48
Specific prefix: 2001:DB8:2222:0000::/64
Specific prefix: 2001:DB8:2222:0001::/64
Specific prefix: 2001:DB8:2222:4321::/64
Specific prefix: 2001:DB8:2222:7744::/64

General prefixes can be defined in several ways:

  • Manually
  • Based on a 6to4 interface
  • Dynamically, from a prefix received by a Dynamic Host Configuration Protocol (DHCP) for IPv6 prefix delegation client

More specific prefixes, based on a general prefix, can be used when configuring IPv6 on an interface.

How to Configure IPv6 Generic Prefix

Defining a General Prefix Manually

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


Example:

Device(config)# ipv6 general-prefix my-prefix 2001:DB8:2222::/48

 

Defines a general prefix for an IPv6 address.

 

Defining a General Prefix Based on a 6to4 Interface

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
ipv6 general-prefix prefix-name {ipv6-prefix/prefix-length | 6to4 interface-type interface-number}


Example:

Device(config)# ipv6 general-prefix my-prefix 6to4 ethernet 0

 

Defines a general prefix for a 6to4 address.

 

Using a General Prefix in IPv6

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    ipv6 address { ipv6-address/prefix-length | prefix-name sub-bits/prefix-length}


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
interface type number


Example:

Device(config)# interface ethernet 0/0

 

Specifies an interface type and number, and places the device in interface configuration mode.

 
Step 4
ipv6 address { ipv6-address/prefix-length | prefix-name sub-bits/prefix-length}


Example:

Device(config-if) ipv6 address my-prefix 2001:DB8:0:7272::/64

 

Configures an IPv6 prefix name for an IPv6 address and enables IPv6 processing on the interface.

 

Additional References

Related Documents

Related Topic Document Title

IPv6 addressing and connectivity

IPv6 Configuration Guide

DHCP configuration

IP Addressing: DHCP Configuration Guide

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

IPv6 commands

Cisco IOS IPv6 Command Reference

Cisco IOS IPv6 features

Cisco IOS IPv6 Feature Mapping

Standards and RFCs

Standard/RFC Title

RFCs for IPv6

IPv6 RFCs

MIBs

MIB

MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for IPv6 Generic Prefix

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1 Feature Information for
Feature Name Releases Feature Information

IPv6 Generic Prefix

12.3(4)T

The upper 64 bits of an IPv6 address are composed from a global routing prefix plus a subnet ID. A general prefix (for example, /48) holds a short prefix, based on which a number of longer, more-specific, prefixes (for example, /64) can be defined.

The following commands were introduced or modified: ipv6 address, ipv6 general-prefix.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2012 Cisco Systems, Inc. All rights reserved.