Today I couldn't remember some software I used 14 years ago to block IP addresses that are attacking your server in a denial of service (DoS) attack. I emailed a colleague and friend who was on the same team with me back then and he replied right away. Awesome.
It turns out I did remember the software that he still uses, which is called fail2ban. The one I forgot is called DenyHosts, which he no longer uses.
He also sent me some helpful commands from his wiki:
To view a list of IP's that are in jail, run:
iptables -L -n
To check the status of Fail2ban, run:
To unblock an IP address, run:
fail2ban-client set ssh-iptables unbanip [XX.XX.XX.XX]