8.1 LAN technology in a cluster the critical link

Like any enterprise server, Windows clustering relies on its connection to the enterprise LAN to provide a reliable communication link with its end user. Because the main goal of this book is to show the reader how to build highly available and scalable systems, the connection to the local area network (LAN) is a very important topic anytime there is a discussion involving clustering. Even though LANs have been deployed since the early 1980s, from our experience one cannot assume that they have necessarily been designed or implemented correctly everywhere they have been installed. In our experience in the field, the LAN connection might well be considered the most fragile link in a cluster implementation. Further, the failure of the enterprise LAN can be blamed for well over half of the service interruptions to end users. Even if you want to assume, for the sake of argument, that most LANs have been deployed correctly, it might surprise you to know how easily a LAN can be brought to its knees. All it takes is for someone to make a very simple and common mistake, not knowing the ramifications of his or her actions, or even a networking administrator who just plain makes a stupid mistake. It's amazing how easy it is for one innocent user to take down a whole building and maybe even a campus.

We witnessed this one day after receiving a frantic call from a network support group employee.