Windows 7 / Networking

How Windows Creates the Network Map

Windows creates the Network Map in part by using the Link Layer Topology Discovery (LLTD) protocol. As the name suggests, LLTD functions at Layer 2 (the layer devices use to communicate on a LAN) and enables network devices to identify each other, learn about the network (including bandwidth capabilities), and establish communications (even if devices are not yet configured with IP addresses). Typically, you do not need to manage LLTD directly. However, you can configure two Group Policy settings located within Computer Configuration\Policies\Administrative Templates\Network \Link Layer Topology Discovery:

  • Turn on Responder (RSPNDR) Driver This setting enables computers to be discovered on a network and to participate in Quality of Service (QoS) activities, such as bandwidth estimation and network health analysis. You can choose to enable the responder driver while connected to networks of the domain, public, or private location type. Windows enables the responder driver for all networks by default.
  • Turn on Mapper I/O (LLTDIO) Driver This setting enables a computer to discover the topology of the local network and to initiate QoS requests. You can choose to enable the mapper driver while connected to networks of the domain, public, or private location type. This option is enabled for all networks by default. Windows enables the mapper driver for all networks by default.

Figure below illustrates how the LLTD responder and mapper relate to other networking components.

LLTD is implemented as a low-level mapper and responder

Note Windows Vista and Windows 7 include an LLTD responder, but earlier versions of Windows do not. To find out how to download an LLTD responder that you can add to Windows XP, read Microsoft Knowledge Base article 992120 at This will enable computers running Windows XP to appear on the Network Maps in Windows 7, but they still cannot generate the maps.

LLTD is not a secure protocol, and there is no guarantee that the Network Map is accurate. It is possible for devices on the network to send false announcements, adding bogus items to the map.

Because each user can have his own set of network profiles, Windows creates Network Maps on a per-user basis. For each network profile that a user creates, Windows actually generates two maps: the current map and a copy of the last functional map (similar to the Last Known Good recovery option). When displaying the Network Map to the user, Windows combines these two maps.

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In this tutorial:

  1. Configuring Windows Networking
  2. Usability Improvements
  3. Network And Sharing Center
  4. Network Explorer
  5. How Windows Finds Network Resources
  6. How Windows Publishes Network Resources
  7. How Windows Creates the Network Map
  8. Network Map
  9. Set Up A Connection Or Network Wizard
  10. Manageability Improvements
  11. Network Location Types
  12. Policy-Based QoS
  13. Selecting DSCP Values
  14. Planning Traffic Throttling
  15. Configuring QoS Policies
  16. Configuring System-Wide QoS Settings
  17. Configuring Advanced QoS Settings
  18. Testing QoS
  19. Windows Firewall and IPsec
  20. Windows Connect Now in Windows 7
  21. Core Networking Improvements
  22. Networking BranchCache
  23. How Hosted Cache Works
  24. How Distributed Cache Works
  25. Configuring BranchCache
  26. BranchCache Protocols
  27. File Sharing Using SMB
  28. Web Browsing with HTTP (Including HTTPS)
  29. DNSsec
  30. GreenIT
  31. Efficient Networking
  32. What Causes Latency, How to Measure It, and How to Control It
  33. TCP Receive Window Scaling
  34. Scalable Networking
  35. Improved Reliability
  36. IPv6 Support
  37. 802.1X Network Authentication
  38. Server Message Block (SMB) 2.0
  39. Strong Host Model
  40. Wireless Networking
  41. Improved APIs
  42. Network Awareness
  43. Improved Peer Networking
  44. Services Used by Peer-to-Peer Networking
  45. Managing Peer-to-Peer Networking
  46. Peer-to-Peer Name Resolution
  47. EAP Host Architecture
  48. Layered Service Provider (LSP)
  49. Windows Sockets Direct Path for System Area Networks
  50. How to Configure Wireless Settings
  51. Configuring Wireless Settings Manually
  52. Using Group Policy to Configure Wireless Settings
  53. How to Configure TCP/IP
  54. DHCP
  55. Configuring IP Addresses Manually
  56. Command Line and Scripts
  57. How to Connect to AD DS Domains
  58. How to Connect to a Domain When 802.1X Authentication Is Not Enabled
  59. How to Connect to a Domain When 802.1X Authentication Is Enabled