Fredrik Tolf wrote:

Ah, I see your point. Very good point, in fact. I guess there are two
ways of solving that. Either make the hub connect to each user to try
him (bad idea, I admit)

eDonkey servers do this - they connect to a user's listening port and if it's unreachable, it puts them in their equivalent of passive mode (lowID).  eDonkey servers also host a lot more users than the biggest DC hubs as of yet do (the biggest I saw listed was 205,628 users - though the median size seems closer to 20-30k).

If a user detects anything weird about another user (not being able to
connect to him,

From my experience on the DC++ forums, if you implement a "warning system" that can be triggered on timeouts by the user, you will get a lot of misconfigured users using it.  (Many behind routers don't realize they have to put in their external IP to become active.)

- Todd