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I have a Vista Ultimate 64 computer (not in a domain) with a file share defined. A second XP SP3 computer accesses the file share. Frequently, when trying to access folders via the command line, the share either stalls out for about 30 seconds or disconnects, despite a previous access 10 seconds ago.

Bringing up and Explorer window from the XP computer and accessing the Vista file share also occasionally stalls out for 30 seconds.

What can I look for to isolate and remove the cause of stalls and disconnects?

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Never seen that. Perhaps network/ethernet card/driver issues? – Will Jul 16 '09 at 13:52

A WireShark network trace showed that the freeze occurs when the Vista computer responds to a NetBios Name query with the IP address of a VMWare virtual network node instead of the primary network interface address. The description of this VMWare virtual network is "A private network shared with the host".

It further turns out that Vista's firewall classifies the VMWare Virtual Network as a "Public Network", and therefore blocks any attempt to access that network from other local computers. Setting the VMWare Virtual Network as private solves the blocking issue.

Update: Setting the Virtual network as private is only a partial fix - the virtual networks revert to public networks after a reboot. The complete fix is to declare them as network endpoints (NDIS_DEVICE_TYPE_ENDPOINT) as demonstrated with the PowerShell script at VMWare VMNET Adapters triggering Public Profile for Windows Firewall . As this MSDN Article shows:

Note: Vista automatically identifies and monitors the networks to which a computer connects. If the NDIS_DEVICE_TYPE_ENDPOINT flag is set, the device is an endpoint device and is not a connection to a true external network. Consequently, Windows ignores the endpoint device when Windows identifies networks. The Network Awareness APIs indicate that the device does not connect the computer to a network. For end users in this situation, the Network and Sharing Center and the network icon in the notification area do not show the NDIS endpoint device as connected. However, the connection is shown in the Network Connections Folder. Also, if NDIS_DEVICE_TYPE_ENDPOINT is set, the Windows Firewall ignores the connection when Windows Firewall enforces public, private, or domain policies.

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Are either of these laptops using wifi? Bad wifi drivers can drop connections periodically, causing you to need to reconnect to shares.

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Both computers are directly connected to the network via a CAT5 cable. – Mike Jul 16 '09 at 13:52

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