ok this one is not easy , and frankly i have no clue how to get it .
Imagine that you buy an used router over ebay witch its configuration is :
-static ip (witch you have no idea the range of it)
- a different subnet config than 255.255.255.0
- reset option blocked in router configuration
now , you want to configure your network card to the router config so you can access its admin webinterface and change the static ip to dhcp , but you do not know either the subnet config or ip range .
Question : How it is possible to find this data ?