dont quote me on this, but i would look in PORT RANGE REMAPPING or NAT TRANSLATION.
Some times its also just a setting in things like PORT FORWARDING (sometimes called SERVICES) where you may have to forward the ports mirc wants to use for dcc to your pc from the router, some routers have a "base port" value, and if set to 63000 it well use that onwards externally but send to your mirc ports as mircs set values, some routers i have seen if its not set at all, it just chooses some 50,000+ number for you, so you have to set it to the same value as the port(s) your forwarding. Would have to really have a look at the router diags to find it for sure.
