Interesting little problem thats got me stumped.
I have a DC setup as a guest, running Win 2k8 R2 (64bit). IP Address = 192.168.1.4 (255.255.255.0).
It has default gateway set to 192.168.1.1 (which is my router) and DNS set to 127.0.0.1 as well as 192.168.1.1 as secondary.
My Host, which is Win 7 64bit, is configured with a dynamic IP from DHCP served from the router. Yes its on 255.255.255.0.
The network in the guest is configured as NAT.
I can't ping the host from the guest.