My network is configured as so:
Vigor2920 with ADSL modem on WAN1 and 3G USB dongle on WAN3 as backup
Server running full Win 2008 R2 with Hyper-V, hosting 3 VMs (one of which is SBS 2011 acting as my DNS and DHCP server)
PC running Win 7 Pro (is a member of the SBS domain)
Laptop running Win 7 Pro (is not a domain member)
The other 2 VMs are:
Win 2008 R2 virtual server (is a member of the SBS domain)
XP SP3 virtual workstation (is not a domain member)

With the ADSL on WAN1 active, all computers can access the Internet without any problems, but, if I disconnect the ADSL modem and let the 3G modem connect (which it does perfectly), none of the VMs can ping any address on the Internet. All of the physical machines still can although, obviously, because my DNS server is on a VM, I have no DNS lookup unless I add the router IP as a second DNS server on each physical system (It makes no difference doing this on a VM though). To check that this problem isn't due the fact that I'm using the 3G dongle as a backup connection, I've tried re-configuring the 2920 so that it only uses the 3G connection; but still none of the VMs can see the Internet at all.
I have recreated the virtual networks in the Hyper-V console from scratch to make sure that I hadn't changed any settings that might be causing this - but without effect.

Any suggestions appreciated (especially if they resolve my problem! :wink: )