Odd Behaviour from Hyper-V Virtual Networks

I recently found myself scratching my head trying to resolve an issue with one of our Hyper-V 2008 R2 host. The network in question had a number of virtual guests attached to it as well as some physical machines, through an attached PCI network card. We were actually trying to build a bunch of PC’s using a virtual SCCM server.

When our task sequence kept failing, It appeared that SMB connectivity to physical machines wasn’t working. Sometimes you could browse to a network location, it would hang for about 20 seconds and then either display the contents of the folder, or simply time out. Interestingly, virtual machines on the same host as the server worked without issue.

After much gnashing of teeth and updating of drivers, I came up with the following solution.

Under Network Connections, right-click the network card that your virtual network is attached to, click Properties.

Click Configure

Under the Advanced tab, select Large Send Offload v2, then select Disabled on the right hand side.

click OK twice.

The reason I say this behaviour is odd, is that we’ve been using Hyper-V 2008 R2 now for ages and never come across this problem until now.