IPv6 Anycast Address - Smartencyclopedia

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.

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.

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 1

Subnet 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 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 tunnel0	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 GigabitEthernet1	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	Specifying the ipv6 address anycast command adds an IPv6 anycast address.

Configuration Examples for IPv6 Anycast Address

Example: Configuring IPv6 Anycast Addressing

 interface tunnel0
   tunnel mode ipv6ip 6to4
   tunnel source ethernet1
   ipv6 address 2001:0db8:1::1/64
   ipv6 address 2002:0db8:6301::/128 anycast
  !
  interface gigabitethernet1
   ip address 10.0.0.1 255.255.255.0
   ip address 192.88.99.1 255.255.255.0 secondary

Source: CISCO