This lesson provides a brief overview of the three categories of IPv6 address types.

  • Unicast - One node communicates with only one other node
  • Multicast - One node sends traffic to multiple nodes simultaneously
  • Anycast - One node communicates with the nearest node in a group
  • *No broadcast


Unicast is for communication between a single node and another single node - this is often called "one to one" communication. This type of address is only assigned to a single interface.

Unicast is used for many things including:

  • A corporate user connecting to an Email server
  • The Email server's reply
  • A home user connecting to a search engine on the Internet
  • The search engine's reply

Unicast: One to One Communication
Unicast: One-to-One Communication


Multicast is used when one node wants to efficiently wants to communicate with multiple nodes.

Let's use an example where an organization wants to train 50 employees at the same time by streaming video. It doesn't make sense to use one server (or multiple servers) to run 50 independent unicast video streaming sessions at the same time. It's much more efficient to run one streaming session and then to split that one session split to the 50 recipients. Note that the recipients could be in the same building or in different locations all over the world!

Multicast scales very well. If the number of 50 recipients increases to 10,000 or more, we don't need to buy and configure more servers to accommodate them. The additional users only need to join the multicast group.

Multicast: One-to-Many Communication
Multicast: One-to-Many Communication


Anycast is used when a node can connect to multiple nodes, but will connect to the nearest one.

For example, if I'm in Canada and I want to connect to my favorite search engine that has locations all over the world, it would be better for me to connect to a search engine server in Canada rather than in England. If I were to travel to England and want to connect to my favorite search engine, it would be better to connect to a search engine server in England. This happens transparently to the user - the user doesn't need to do or know anything.

Another great feature of Anycast is failover. If the England server were to fail, it would no longer be the nearest...the USA server would be. The England host would be re-directed to the new nearest...the USA server.

Anycast: One to Many
Anycast: One to Many

No Broadcasts

Broadcasts can cause significant problems with respect to security, bandwidth and CPU overhead. IPv6 completely eliminates the use of broadcasts and uses multicasts instead.


In this lesson, we took a brief look at the three main categories of IPv6 address types. In the next few lessons, we’ll take a look at each of these address types in more detail.

IP Version 6 Addressing Architecture

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