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A Win7-32 guest loses its bridge network connection and when the connection is lost, incoming and outgoing pings fail, even to the host. The failure happens seemingly randomly - might run anywhere from a day to 5 minutes before it fails. This problem just appeared for the first time a few days ago. When the problem occurs, the other VMs retain their network connections. I can get the Win7-32 guest to recover its network connectivity by disabling and re-enabling the network adapter on the guest side - I do this using the Network Connections dialog or by using netsh. Doing a virtual-connection unplug & re-plug on the host VirtualBox app has no effect. Event logs on the Win7-32 guest show nothing other than DNS errors that result from the lost connection. This particular Win7-32 guest is running just a license server - doesn't get much traffic.

Any suggestions to trouble-shoot this problem? The problem seems to be isolated to the Win7-32 guest but there have been no changes to this VM for several months. I did add another VM (the 4th) to the host - this was about 2 weeks ago. The problem started about 4 days ago.

Particulars:
Guest is Win7-32, one of 4 VMs running on the host
Win7-32 Guest has had no Windows updates applied to it for over a year
The Guest virtual network adapter is an Intel Pro/1000 MT 82540OEM configured for bridge mode with a static IPv4 address. IPv6 is disabled.
Host is VirtualBox 4.1.6 running on Suse 11 (both fairly old but they've been running OK for more than a year).

That sort of thing is usually caused by a problem with the physical NIC (or its driver) in the host machine. These have to work with the VirtualBox bridged networking driver to allow the guest to share the NIC with the host.

BillG-
Would you suspect the NIC even if other VM's using that NIC retain their network connection? I'm wondering if netowrk loading on the NIC is causing this one particular VM to drop its connection.

As a work-around, I'm using a script on the guest that does a 'netsh enable & disable' if pings to the host fail. Not a proper fix but it works ok so far. This host is due to be replaced soon.
All other guests on this host seem to retain their network connections.