Overnet client port. That port must be open for both TCP and UDP protocols. Remark: each client select a random overnet port when first run; But the selected port is saved across sessions in downloads.ini, so it will stay the same after that (unless you modify that parameter manually, of course).
Note that overnet uses edonkey port for file transfers.
_If it does, then it's a bug. MetaMachine modified the Overnet protocol to be slightly incompatible with the Donkey protocol, so networks must be handled differently (hence on different ports)_
This option is stored in donkey.ini
On first run, an overnet_port number will be picked randomly between 2000 and 21999.