Site 1 - IP Range 192.168.1.x/24
Site 1 Gateway 192.168.1.4
Site 2 - IP Range 192.168.2.x/24
Site 2 Gateway 192.168.2.1
There is a VPN between the two sites (using a Firebox X550e at one end, and a Draytek Vigor 2800 at the other)
I can quite happily access PCs on both networks from either site.
HOWEVER, a telephone company has been contracted to install an Avaya IP Phone system.
At site 1, they can ping their phone system which is on IP 192.168.1.250, but they cannot ping the phone system at site 2 which is on IP 192.168.2.250 - and vice versa.