The following happens when an application requests a network resource using the Uniform Naming Convention (UNC):

1. The request is received by the Multiple UNC Provider (MUP)
2. The MUP checks it's cache for a recent handle to the wanted resource (Since the last 15 Minutes) if available it is returned
3. The MUP goes through the available network redirectors and ask them if they know the wanted resource (Sorted by priority)
4. Each network redirector responds back with a handle to the wanted resource if available (Asked synchronously)
5. The MUP returns the handle from the redirector which responds back first (Highest priority).

One should make sure the redirectors/providers (Like "Microsoft Client for Microsoft Networks" or "Novell Client for Novell Netware"), which knows the majority of the wanted network resources, has the highest priority.

To configure the priority of redirectors in WinNT4:

1. Open Control Panel
2. Double click Network applet
3. Select Services tab
4. Click Network Access Order

To configure the priority of redirectors in Win2k/WinXP:

1. Open Control Panel
2. Double click Network and Dial-Up Connections
3. In the menu select Advanced and select Advanced Settings...
   • Vista will only display the Advanced menu-item when pressing the ALT-key
4. Select the Provider Order tab and set the priority of Network Providers

Note by default the Distributed File System (DFS) is always asked first (Independent of priority), this can be disabled with this registry key (Causes BSOD with the Mup.sys in Win2k SP4 (MS KB824288))

[HKEY_LOCAL_MACHINE \System \CurrentControlSet \Services \Mup]
DisableDfs = 1 (Default = 0)

More Info MS KB259398
More Info MS KB314494

Note MUP.SYS is usually the last driver being shown before launching the operating system, and if there is a problem with loading Windows, then it might seem like MUP.SYS is causing the problem (But it is not).

More Info MS KB171386

Related Configure the priority of network adapter and gateways
Related Configure the priority of protocols bound to the network redirector