Two methods are used to locate network resources for the redirector:
- MUP - Multiple Universal Naming Provider (MUP) allows the client to search for or browse for network resources using their UNC name.
- MPR - Multiple Provider Router ensures that network resource requests on computers with multiple redirectors and networks are routed to the appropriate network redirector. The MPR caches the request for a period of time after it has been established.
Browser service is a provider of a list of network resources which does not affect access. Browse List - A list of available resources on the network domain. The size of this list is limited to 64K limiting the number of domain computers to 2000 to 3000.
Each domain has one domain master browser. Each workgroup or domain subnet has one master browser and at least one backup browser. There can be up to three backup browsers. The master browser normally selects one potential browser for every 32 computers on the domain.
- Master Browser - Maintains the main or master list of computers and shared resources. All workgroups or domains have one master browser. A new resource list is sent to the backup browsers every 15 minutes. A client will not be removed from the resource list for 3, 12 minute periods. Another domain master will wait 3 15 minute periods of no response from a domain master browser before removing the domain resources from its list. The client will first go to the master browser which will give the client a list of backup browsers.
- Domain Master Browser - The master browser for a domain. The primary domain controller (PDC) in a domain network always wins elections to become the domain master browser.
- Subnet Browser or Local Master Browser - Works on a subnet providing resource lists to the clients and keeping the Domain Master Browser updated with resource lists. This is normally a backup domain controller (BDC). This browser must have support for a routable protocol such as TCP/IP or IPX/SPX. An assumption here is that the domain master browser is on a different subnet.
- Backup Browser - The domain master browser sends a copy of the browse list to the backup browser periodically in case the master fails. This browser is also responsible for passing the browse list to clients.
- Potential Browser - A computer that may become a master or backup browser.
- Non-Browser - A computer that will never become a browser.
Browsing across Subnets
If a windows network is a routed network, here are some options that may be used to allow browsing across subnets:
- Enable NetBIOS broadcasts and mailslots announcements on the routers.
- Clients use a local lmhosts file for name resolution for computers they want to access resources on.
- WINS - When a computer configured for WINS begins operation and sends a broadcast, it sends its name and IP address to the WINS server. TCP/IP must be bound to the computers to use WINS (or the subnet master will contact WINS?).
When a computer boots, it will announce itself and their criteria for becoming a browser. The election is based on the potential roles, and operating systems listed below. The server type of the machine influences its election criteria. Once elected, the master browser will assign one or more backup browsers. When a computer becomes the master browser it will broadcast a domain announcement to all other domains or workgroups.
Potential Browser Roles
Election based on potential role:
- Preferred Master
- Backup Browser
- Potential Browser
Election based on operating system:
- PDC Win NT server
- Win NT server
- Win NT workstation
- Windows 95
- Windows for workgroups
Election based on NT version
Beyond that the election is based on the computer that is running the longest, then alphabetic order by computer name. If a computer is set to be the preferred master browser, only a PDC can win the election over that computer. The election process is as follows:
- An election packet is broadcast by a computer because of a situation such as the master browser failed to respond. Until the election is complete, the network is in an "election in progress" state.
- Any computer with a higher presidence than the last election packet broadcast will respond with its own election packet.
- The computer that broadcast the last election packet with no response within a given time becomes the master browser.
Browser registry settings on the workstation are at:
- MaintainServerList - If value is:
- No - Workstation will not be a browser
- Yes - The workstation may be a browser or backup browser.
- Auto - The workstation may become master, backup, or potential browser.
- IsDomainMaster - Default is No. If set to Yes, only a PDC can win the election over the workstation with this setting.
How browsing works
Upon bootup, members of the domain or workgroup announce themselves to the master browser once a minute for 5 minutes then every 12 minutes afterwards. They do this by sending a server announcement packet to the master browser. If a computer sharing resources does not respond for three announcement periods of 12 minutes each, the master browser removes that computer from its browse list. If the computer is shutdown normally, it tells the master browser.
Backup browsers poll the master browser every 15 minutes to receive the browse list. Backup browsers send messages to the master every 15 minutes. The master browser won't remove a backup browser from its list for three announcement periods or a total of 45 minutes. Since the clients will ask the master browser for a list of backup browsers, then ask a backup browser for the browse list information the maximum time a resource may be unavailable, but still appear on the browse list to the client is 51 minutes. This is three 12 minute announcement periods for computers sharing resources plus the maximum time for the latest browse list to be sent to the backup browsers which is 15 minutes.
The master browser can send a request announcement packet requiring all computers in the workgroup or domain to respond within 30 seconds. Master browsers on separate domains listen for broadcasts from each other. For five minutes after becoming master, the computer will send domain announcement messages every minute to other domains. It then repeats this process every 15 minutes. If a domain master browser has not sent messages for three time periods, which is 45 minutes, other browsers will remove that domain from their browse list.
Number of Browsers
There can only be three backup browsers in a domain. If the "MaintainServerList" parameter on a workstation is set to "auto" one potential browser is selected by the master browser to be a backup browser for every 32 computers on the network. In a routed subnet, the PDC acts as a domain master browser to coordinate all subnet master browsers using WINS. All BDCs are automatic browsers except when a BDC must act as a master browser when the PDC is not available.
Browsing Across Subnets
NWLink passes broadcasts through its routers, but TCP/IP does not. On subnets, there must be a subnet master browser. The subnet master browser and the domain master browser swap browse lists. On TCP/IP, port 137 is used for browser broadcasts.
Joining a domain
On a domain controller, the server manager program is used to create an account for a computer for it to become a member of a domain.