How Windows Finds Network Resources

Versions of Windows prior to Windows Vista use NetBIOS broadcasts to announce their presence on the network to facilitate finding shared resources in workgroup environments. Windows Vista and Windows 7 expand this capability with a feature called Network Discovery, also known as Function Discovery (FD). Network Discovery's primary purpose is to simplify configuring and connecting network devices in home and small office environments. For example, Network Discovery can enable the Media Center feature to detect a Media Center Extender device (such as an Xbox 360) when it is connected to the network.

Network Discovery can be enabled or disabled separately for different network location types. For example, Network Discovery is enabled by default on networks with the private location type, but it is disabled on networks with the public or domain location types. By properly configuring network location types (described later in this tutorial), computers running Windows Vista and Windows 7 in your environment can take advantage of Network Discovery when connected to your internal networks but minimize security risks by disabling Network Discovery when connected to other networks, such as the Internet. You might want to leave Network Discovery enabled for some network location types so that users can more easily find network resources on your intranet that aren't listed in Active Directory Domain Services (AD DS) and so that users with mobile PCs can configure network devices more easily on their home networks or when traveling.

Although Network Discovery is preferred, Windows Vista and Windows 7 continue to use the Computer Browser service and NetBIOS broadcasts to find earlier versions of Windows computers on the network. In addition, Windows Vista and Windows 7 use the Function Discovery Provider Host service and Web Services Dynamic Discovery (WS-Discovery) to find other Windows Vista and Windows 7 computers and use Universal Plug and Play (UPnP)/ Simple Service Discovery Protocol (SSDP) to find networked devices that support the protocols. Therefore, enabling Network Discovery creates exceptions for each of these protocols through Windows Firewall.

WS-Discovery is a multicast discovery protocol developed by Microsoft, BEA, Canon, Intel, and webMethods to provide a method for locating services on a network. To find network resources, computers running Windows Vista and Windows 7 send a multicast request for one or more target services, such as shared folders and printers. Then, any computers on the local network with shared resources that match the request use WS-Discovery to respond to the message. To minimize the need for clients to regularly send requests to find new resources, newly published resources announce themselves on the network, as described in the next section.

WS-Discovery uses Simple Object Access Protocol (SOAP) over UDP port 3702. The multicast address is 239.255.255.250 for IPv4 and FF2::C for IPv6.