IPv6 Anycast Address
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IPv6 Anycast Address

Last Updated: August 15, 2012

An IPv6 anycast address is an address that is assigned to a set of interfaces that typically belong to different nodes. Anycast addresses are syntactically indistinguishable from unicast addresses, because anycast addresses are allocated from the unicast address space.

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 Anycast Address

IPv6 Address Type: Anycast

An anycast address is an address that is assigned to a set of interfaces that typically belong to different nodes. A packet sent to an anycast address is delivered to the closest interface (as defined by the routing protocols in use) identified by the anycast address. Anycast addresses are syntactically indistinguishable from unicast addresses, because anycast addresses are allocated from the unicast address space. Assigning a unicast address to more than one interface makes a unicast address an anycast address. Nodes to which the anycast address is assigned must be explicitly configured to recognize that the address is an anycast address.


Note
Anycast addresses can be used only by a device, not a host, and anycast addresses must not be used as the source address of an IPv6 packet.

The figure below shows the format of the subnet device anycast address; the address has a prefix concatenated by a series of zeros (the interface ID). The subnet device anycast address can be used to reach a device on the link that is identified by the prefix in the subnet device anycast address.

Figure 1Subnet Device Anycast Address Format


How to Configure IPv6 Anycast Address

Configuring IPv6 Anycast Addressing

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.   tunnel mode ipv6ip [6rd | 6to4 | auto-tunnel | isatap]

5.   tunnel source {ip address | ipv6-address | interface-type interface-number}

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

7.    ipv6 address ipv6-prefix/prefix-length anycast


DETAILED STEPS
 Command or ActionPurpose
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 tunnel 0

 

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

 
Step 4
tunnel mode ipv6ip [6rd | 6to4 | auto-tunnel | isatap]


Example:

Device(config-if)# tunnel mode ipv6ip 6to4

 

Configures a static IPv6 tunnel interface.

 
Step 5
tunnel source {ip address | ipv6-address | interface-type interface-number}


Example:

Device(config-if)# tunnel source Ethernet1

 

Sets the source address for a tunnel interface.

  • The address used here is the one assigned to Ethernet interface 1.
 
Step 6
ipv6 address { ipv6-prefix/prefix-length | prefix-name sub-bits/prefix-length}


Example:

Device(config-if)# ipv6 address 2001:db8:A00:1::1/64

 

Configures an IPv6 address and enables IPv6 processing on an interface.

 
Step 7
ipv6 address ipv6-prefix/prefix-length anycast


Example:

Device(config-if)# ipv6 address 2002:db8:c058::/128 anycast

 

Adds an IPv6 anycast address.

 

Configuration Examples for IPv6 Anycast Address

Example: Configuring IPv6 Anycast Addressing

 interface tunnel 0
   tunnel mode ipv6ip 6to4
   tunnel source ethernet1
   ipv6 address 2001:0db8:1::1/64
   ipv6 address 2002:0db8:6301::/128 anycast
  !
  interface ethernet 1
   ip address 10.0.0.1 255.255.255.0
   ip address 192.88.99.1 255.255.255.0 secondary

Additional References

Related Documents

Related Topic Document Title

IPv6 addressing and connectivity

IPv6 Configuration Guide

IPv4 addressing

IP Addressing: IPv4 Addressing 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 Anycast Address

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 1Feature Information for IPv6 Anycast Address
Feature Name Releases Feature Information

IPv6: Anycast Address

12.2(25)SEA

12.2(25)SG

12.2(33)SRA

12.2(33)SXH

12.3(4)T

15.0(2)SG

Cisco IOS XE Release 2.1

3.2.0SG

An anycast address is an address that is assigned to a set of interfaces that typically belong to different nodes. Anycast addresses are syntactically indistinguishable from unicast addresses, because anycast addresses are allocated from the unicast address space.

The following commands were introduced or modified: ipv6 address anycast, show ipv6 interface.

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.