Last day I was working in a server with heavy ddos, nothing seems to be working. I tried tweaking kernel parameters and also installed mod_evasive but no luck. At last I gave a try with CSF, and it worked !!

You just need to configure two csf directives, thats it.

The two directives are PORTFLOOD and SYNFLOOD.

SYNFLOOD

SYNFLOOD is disabled by default. If you are not receiving any sort of attack, there is no need to enable it. If you are expecting an attack, enable it and set the rules a bit strict, like

SYNFLOOD = “1″

SYNFLOOD_RATE = “30/s”

SYNFLOOD_BURST = “10″

i.e. if 30 connections are received from an IP/sec for 10 times, block it. Make sure don’t keep it too strict if you are not receiving an attack else it will generate false positives and will block legit connections.

PORTFLOOD

PORTFLOOD = 80;tcp;100;5,22;tcp;5;300

ie, If an IP makes 100 connections in 5 sec to port 80 (tcp), then it will be blocked from the server and if 5 connections in 300 sec to 22 port.

PORTFLOOD = 80;tcp;100;5,22;tcp;5;300

ie, If an IP makes 100 connections in 5 sec to port 80 (tcp), then it will be blocked from the server and if 5 connections in 300 sec to 22 port.