nowadays it seems like everything contains a "firewall" of some kind because Internet access is so universal.
I kind of meant firewalls generically, but for sure the functionality varies between different firewall implementations. That is why I refered specifically to the IPTABLES firewall available on Linux, which allows quite complex rules definitions based on protocol, IP address ranges, subnets, direction, etc., either to allow or disallow transit across the firewall.
The firewall on your PC also has some functionality of that nature. I know that because some time ago I had to enable Windows XP firewalls to respond to ICMP in order to do troubleshooting on a LAN on which I was working.
I also remember that on XP, it was possible to allow or disallow communications based on the port to be used.
I just checked Windows 7 which I just intalled on my laptop. Of course, Microsoft has changed the firewall user interface (go figure, if it ain't broke, why fix it????) and it seems entirely different than XP, being based on the program communicating, and whether it is for the external or local network. I haven't the time or requirement right now to research it more deeply, but I know in my gut that some day I will likely have to figure the new interface out as well.
I just wanted to register so that I could put my 2 cents.
A DDOS attack is a legitimate problem that should be handled by an internet service provider, otherwise the victim can go to the police and have the police do your job for you. (google cybercrime unit)
Now, the reason this ISP doesn't want to give him a new IP is because IPs cost money!
Your horrible service and attitude precedes even the finest of aspects about your fiber optic lines (if any) and your list of owned IP addresses.