Anycast Confusion

Ahh... anycast... perhaps the most mysterious of them all. After learning about IPv4, many people who have been taught some basics about IPv6 have heard the term “anycast”, but have not heard an explanation that they really understood solidly.

Probably the main reason why the topic of “anycast traffic” gets frequently mentioned (for instance, in training material) when people are taught about IPv6 basics is probably because anycast traffic gets covered by RFC 4291. (Specifically, it is covered by RFC 4291: IPv6 Addressing Architecture, section 2: “IPv6 Addressing” (in the first part of section 2, before the subsection 2.1) and RFC 4291 section 2.6: “Anycast Addresses”.)

Since many people learned that IPv6 uses multicast more than IPv4, and anycast traffic is described in the documentation near the sections that describe multicast, people probably assumed that anycast may also be an important part of IPv6. Then, they get taught that anycast may not be a topic that they need to know much about right now. So, people are left to figure that anycast may become more prominent in the future, and so there may be a need to become familiar with anycast (sometime, perhaps in the future).

Instead of learning details about anycast, people learning about IPv6 just learn that there is something called “anycast” that they may wish to study after they have mastered other IPv6 technologies.

Probably adding to the confusion, anycast does frequently get explained very poorly, perhaps in part because often the people explaining anycast may themselves have very little solid understanding/comprehension of what it is.

Despite all of this confusion, anycast actually is not really a terribly challenging concept.

Details about Anycast, and other types of network traffic, are provided by the network traffic destinations tutorial.