It is likely under the *Security* section that you have multiple functions to protect you from a DoS attack.
I suspect DoS attacks would be illegal but some a-holes don't care. When they are caught their new best friend, cellmate Bubba, will teach them otherwise.
You can do almost nothing. Some simpler attacks where they try to open too many sessions you might prevent but there is nothing you can do if they try to send 100m of data down a 10m connection.
Unplug your ISP connection (fiber/cable/adsl modem) and plug it after some 5 minutes and you might acquire a new ip adress as long as you dont have a static IP address.