1. What is WINS?
PCs linked using Microsoft networking use NetBIOS to communicate with each other (although this is beginning to change with Windows 2000), and in order for one PC to find another (e.g. for a workstation to locate a domain controller), the PCs involved must each have a unique identifier, namely the the NetBIOS or Computer Name. For Windows 95, 98, Me and NT the NetBIOS name is entered in the Network Identification tab in the Network control panel while in Windows 2000 the Network Identification tab in has moved to he System control panel.
In a simple arrangement, when a PC with a NetBIOS name of FROG starts up on subnet A, it broadcasts its existence onto that subnet. Usually that broadcast will not be routed outside the subnet. Within subnet A, one or more PCs will act as a Browse Master and maintain a browse list of the NetBIOS names of all computers currently active on the subnet. Generally any other Windows PC on that subnet will have no trouble in locating it, either explicitly or through browsing the network via Network Neighborhood. For example if a second PC, TOAD, also on subnet A, needs to access a share on FROG, it can use the browse list to locate FROG, or if FROG is not on the browse list it can broadcast to locate it. (Note that Windows 9x PCs will not appear in the browse list unless File and Print Sharing is enabled).
Now since in general NetBIOS broadcasts do not cross routers, if a third PC called NEWT on subnet B needs to be able to access a share on FROG, it will not be able to find FROG. FROG has not broadcast its existence onto subnet B, so no PCs on this subnet will know about it. A method of name resolution is required and this is where WINS comes in. If NEWT and FROG are both both configured to use the same WINS server, the something along the lines of the following steps will take place.
- When PC FROG starts up, it sends a registration request to the WINS server for name FROG, together with FROGs IP address. So long as the name FROG doesnt already exist in the WINS database with a different IP address, the request will be accepted, and the mapping between FROG and FROGs IP address will be entered into the WINS database.
- When PC NEWT starts up, a similar process takes place to register NEWTs name and IP address into the WINS database.
- When someone tries to access a share on FROG from NEWT, NEWT will query the WINS server for the name FROG. The WINS server will respond giving FROGs IP address, and NEWT will be able to access the share on FROG.
It is not simply the PC name that is registered in the WINS database. In fact, the services that the PC is running are also entered. For example, a typical server will have three entries — one each for the workstation, server and messenger services. A domain controller also registers entries for the domain name; an Exchange server adds a couple more entries, as does IIS, and so on and so forth.