You are right, of course, my netmask story is total crap and it was just a coincidence that it worked when I changed it. I put it back and of course 255.255.255.0 works too (phew :-). As I mentioned in another thread a simpler (and less bandwidth-intensive) way to keep the connexion alive from outside is to continuously ping the 770 from a windows console (ping -t ...) or a Linux term (ping -i 4 ...).