Like other administrators and users, I’m happy for the release of Windows 7 and Server 2008 R2. While Windows 7 is touted as more of a client operating system revival from the poor reception that Vista had on the market, Windows Server 2008 is a less controversial and natural upgrade of the server operating system. Both products were released at the same time and have quite a bit in common. One item that both have in common is support for both IPv4 and IPv6 running on default installations. Both also have two new networking protocols running: the Link-Layer Topology Discovery Mapper I/O Driver and Link-Layer Topology Discovery Responder.

Thus far, I’ve simply turned off IPv6, both of the new protocols, and sometimes the QoS Packet Scheduler depending on my mood. Regarding the two new protocols, what are they and what do they do?


Link-Layer Topology Discovery

The Link-Layer Topology Discovery (LLTD) is a component of the Windows networking implementation that allows computers and other devices to be represented on a map. Windows Vista, Windows Server 2008, and Windows 7 computers can natively populate the Network Map. This is visible in the Network and Sharing Center by selecting See Full Map. Each computer that is discovered can be displayed in this map. Settings that go for each type of network (public, home, work, etc.) dictate behavior for these networks. Somewhat unintuitively, if a network is set to a private-class network, the default settings allow for LLTD operation. If the protocols are removed from the networking stack, LLTD will not work.

The two components for LLTD are the responder and the mapper I/O driver. These components work together to populate and enumerate the maps. Figure A shows a map populated on my private network for two LLTD-enabled systems.

Figure A

This shows that W-RWV2 and S-RWV3 are on different switches (which they are) and are connected to the same Internet uplink. I mentioned earlier that this service is usually not enabled, and the systems at the bottom are a mix of Windows XP, Server 2003, and Linux systems. For Windows XP Systems, they can be enumerated in the LLTD maps. Be sure to check this post by Greg Shultz to enable LLTD on XP.

In my networking practice, I haven’t used this feature and disable it on servers. I tend to rely on DNS and networking tools to get from point A to B. Do you see LLTD as a benefit in your networking requirements? If so, share your comments below.