The other day when I was diagnosing some home networking problems on my Windows Vista machine, I stumbled across a new piece of technology from Microsoft: the Link Layer Topology Discovery Protocol. Basically, it does what its name says: it discovers your network topology. Vista uses this to draw a network map where you can see items like other PCs in your home network, routers, printers, security cameras or any other device that supports LLTD:

There are a few caveats. First of all, Microsoft explains in its specification:

“Note that the LLTD protocol operates at Layer 2 in the OSI reference model and as such is not routable. The protocol is suitable only for networks comprising a single subnet, such as a small office network or a home network.”

So you won’t be using this tool to draw a map of a segmented corporate network… (for those of you who never knew what the OSI reference model was – or forgot – here it is on the Wikipedia).

Another caveat – you will only see devices or machines that respond to LLTD. Right now, there are not a whole lot of devices that know what LLTD is, although expect that to change soon with vendors such as Linksys and D-Link adding support to their new networking products. You will see other Vista machines, but not XP machines. However, there is a download of an LLTD Responder for XP which, when installed, allows your Vista machines to see the XP machines too. You can download the responder here.

LLTD also has some extensions for diagnosing and specifying QOS parameters.

And here is another interesting tidbit of informatin… Xbox 360 has LLTD! Oh – and LLTD is part of a whole set of technologies aimed at easing network management for home users and gamers, called Windows Rally.