IPv6 II: Addressing Types

File:Big and little dog 1.jpg

DIFFERENT (aka, not the same!)

As is the case with anything new and unfamiliar, IPv6 can appear  strange, hard to understand, and downright confusing!  Often, when learning new content, it helps to compare or even anchor the concepts in something more familiar, as depicted above with the photo of two very different dog breeds.  In this example, the contrast is plainly visible; one dog towers over the other, and each have variances in coloring, build, and a dozen or more differences.  Even so, both are still dogs, with four legs, a keen sense of smell, ability to learn, and even “man’s best friends.”  Even though the differences may appear vast, the similarities are much greater in number.  This is precisely the case with IPv6, as it represents a different “breed” or “species” of the Internet Protocol, but with many similarities to its predecessor; think of IPv6 as IP 2.0!  One are, which we shall consider now, has to do with addressing types in this new version of the Internet Protocol, namely the types of multicast, anycast, and unicast.


In IPv4, multicast addressing was encompassed the Class D space of –, and used to address multiple hosts.  Broadcast addressing, on the other hand, sent messages to every host on the LAN/VLAN segment in question.  As mentioned previously, IPv6 eliminated the use of broadcasts, in favor of multicast functionality.  Formatting of multicast addresses in IPv6 requires use of the prefix FF, and the basic mechanics are the same as IPv4.


To even seasoned engineers, the concept of anycast addressing can sound confusing and rather contradictory, as it calls for the use of identical addressing on multiple devices.  To be frank, I myself struggled with this for years before inadvertently stumbling on an explanation that made the idea much clearer in my mind.  Anycast is often used on servers to provide resiliency, such as is the case on DNS servers, and often used by service providers for this every purpose.  IP routing directs the requesting device to the nearest server using standard routing metrics which can provide load-sharing as well as failover capabilities.  To better understand this, think of the process by which an end-user utilizes a SmartPhone or GPS device.  The user enters the name of a familiar grocery store, for example (Safeway, Albertsons, etc.), and may get half a dozen responses, along with the distance to reach each one.  ALL the stores have the same name, but each is a different distance from the standpoint of the user, who normally selects the CLOSEST.  This is precisely how anycast addressing works.


Unicast addressing in IPv6 operates the same way as it does in IPv4, but has a number of subtypes, which will be addressed in the next article.

– Joe (Twitter: @jjrinehart)

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