[Bridged networking] Guest machine loses connectivity after a while

[Ecco]

• Host running Mac OS X 10.7, guest running latest Debian stable.
• Guest configured to use bridged networking with the host's ethernet card (no WiFi involved).

Everything works just fine after boot : the guest has internet access, and anyone on the host's subnet can ping the guest. Here's the list of IP addresses :

• Router : 192.168.0.1
• Host : 192.168.0.3 (static DHCP lease set up on the router)
• Guest : 192.168.0.2 (static DHCP lease set up on the router as well)
• Some other laptop on the same network : 192.168.0.6

Initially, anyone here can ping anyone. Of course it's not limited to ICMP traffic, any IP packet can be exchanged just fine between any of those hosts. And the router doing its job, with anyone on the internet too.

Now here's the issue: after waiting a random amount of time (between an hour and a day), the guest partially loses network connectivity. It can actually still send IP traffic to the host, but everything else will fail. Namely, pinging anyone else on the host's subnet will fail, pinging the router will fail, and obviously any internet traffic will fail. So, in terms of IP addresses, 192.168.0.2 can exchange IP traffic with, and only with 192.168.0.3. Traffic between hosts other than the guest still works just fine.

Here are some interesting facts :

• I believe this has nothing to do with the guest itself: rebooting the machine ("shutdown -r now") will *NOT* fix the issue. The guest sure does reboot, but it still doesn't have the issue.
• Reseting the virtual machine ("VBoxManage controlvm VirtualMini acpipowerbutton" and then "VBoxManage startvm "VirtualMini" --type headless") DOES fix the issue. For a while, that is.