1. Blocking the Attack with Packet Filters on the Router(s)
2. Blocking the attack by configuring Firewall.
3. Null Routes
Log files can be useful both in tracking down and stopping the attack. If several ISPs cooperate, it may also be possible to find out who the hacker really is using these logs. If you are still considering pursuing legal actions against the attacker, you will certainly want to keep these for your records; logs often get automatically deleted after a period of time.