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Under the Surface of Azeroth:
A Network Baseline and Security Analysis
of Blizzard's World of Warcraft
The Available Realms

In World of Warcraft, a realm is a self-contained universe of Azeroth. Although the realms are virtually identical "worlds" with the same cities and landmarks, the rules of play may be different across realms. The realms cannot communicate with each other, and players who have characters on one realm cannot interact with characters on another realm. Moving characters from one realm to another can't be done without Blizzard's intervention, and there's a charge for the service. Although there are some administrative reasons for this, this policy may also be based on some valid game play and fraud-protection concerns.

It's this realm-based structure that allows Blizzard to scale their online service to allow an increasing number of simultaneous players. As one realm reaches peak capacity, the ability to add new characters into that realm is disabled and new realms are opened to supply the new demand.

As of this writing, there are two-hundred and twenty-two (222) realms around the world. During the login process, the name of every realm is downloaded to the World of Warcraft client, along with its corresponding IP address and TCP port number. In our example, this occurs in frames 12 through 21.


This realm-to-IP matching process is similar to the way that TCP/IP's Domain Name Services correlate a hostname to an IP address. Since Azeroth isn't a registered Kingdom with the Internet Assigned Numbers Authority (IANA), the Horde and the Alliance have to handle the name resolution of realms themselves. :)

This is a list of every realm definition contained in these frames, in the same order as they appear:


Sending the details of every realm's name, IP address, and port number to the client seems to be a bit inefficient. An end user can only be connected to a single realm at a time, and many users don't often move between realms. This isn't a huge inefficiency, since this download only consists of a few frames and takes less than a second over dialup lines.