It's important to start learning how to identify IPv6 addresses if you want to be able to troubleshoot network connectivity issues on IPv6 networks, and this is especially important as IPv4 to IPv6 migrations accelerate in different parts of the world. One common type of IPv6 address is the link-local address, a unicast address that is used by neighboring nodes on the same network link (that is, not separated by routers). Think of link-local addresses as the IPv6 form of Automatic IP Address Allocation (APIPA), a mechanism used by Windows computers to automatically assign themselves address of the form 169.254.x.y when a DHCP server is unavailable and no static addresses have been assigned. Link-local addresses are similarly self-assigned, and you can always recognize them by opening a command prompt on your computer and typing ipconfig. If the IP address displayed for your computer starts with fe80:: then you've got a link-local address that has been self-assigned using the Neighbor Discovery process used by IPv6. You can test this in Windows Vista, for example, since this platform has IPv6 enabled by default. The limitation of link-local addresses is that IPv6 routers cannot forward link-level traffic outside the link.
Mitch Tulloch is President of MTIT Enterprises, an IT content development company based in Winnipeg, Canada. Prior to starting his own company in 1998, Mitch worked as a Microsoft Certified Trainer (MCT) for Productivity Point International. Mitch is a widely recognized expert on Windows administration, networking and security and has written 14 books and over a hundred articles on various topics. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy Microsoft platforms, products and solutions. Mitch is also a professor at Jones International University (JIU) where he teaches graduate-level courses in Information Security Management (ISM) for their Masters of Business Administration (MBA) program. For more information see http://www.mtit.com.