Anycast

Anycast addresses provide one-to-nearest (one to one-of-many) communication.

Anycast addresses provide one-to-nearest (one to one-of-many) communication.

An anycast address designates a set of interfaces that share an address.

A packet sent to an anycast address goes only to the nearest member of the group. Considering routing distance, the system delivers packets with anycast addresses only to the nearest member of a group of multiple interfaces.

Restrictions

An anycast address must not be:
  • used as the source address in an IPv6 packet

  • assigned to an IPv6 host (you can assign an anycast address to an IPv6 router)

Anycast address scopes

Anycast addresses have the following scopes:
  • Link-local—the local link; nodes on the same subnet

  • Global—IPv6 Internet addresses

Similar to anycast IPv4 addresses, IPv6 anycast addresses are more efficient. They use the unicast address space but identify multiple interfaces.

IPv6 delivers a packet bearing an anycast address to the nearest interface identified by the address.

Currently anycast addresses are assigned to routers and are used as destination addresses. Because packets bearing anycast addresses are delivered to the closest router, you can also access the closest name server or time server with an anycast address.

Visually there is no distinction between an anycast address and a unicast address.

Note

Note

The switch supports only the subnet-router anycast address.

You cannot configure any specific anycast addresses beyond the automatic, generic subnet-router anycast address.