Preventing DDOS attack from csf firewall.

First make sure DDOS attack is not from open recursive DNS settings. To check and fix that issue please read this article – Preventing DDOS aplification open resolver attack

This article is to set CSF firewall so that any DDOS intentional attack to your server can be prevented.

 

Step 1: open and edit CSF config file. 

vi /etc/csf/csf.conf

 

Settings: 

Enable connection tracking.
CT_LIMIT is max number of connection allowed from one IP, you can set this value as per your server requirement.

CT_LIMIT =100

Set connection tracking interval.

CT_INTERVAL =30

If you want to get possible ddos attack email then enable it.

CT_EMAIL_ALERT =1

If you want to make IP blocks permanent then set this to 1, otherwise blocks
will be temporary and will be cleared after CT_BLOCK_TIME seconds

CT_PERMANENT = 1

If you opt for temporary IP blocks for CT, then the following is the interval
in seconds that the IP will remained blocked for (e.g. 1800 = 30 mins)

CT_BLOCK_TIME = 1800

If you only want to count specific ports (e.g. 80,443) then add the ports
to the following as a comma separated list. E.g. “80,443”

CT_PORTS = 80,23,443

 

These settings will be enough for DDOS attacks but if you are getting more attacks even you have above option configured then we can set few more options.

 

Step 2: Enable distributed attacks

LF_DISTATTACK = 1  

Set the following to the minimum number of unique IP addresses that trigger
LF_DISTATTACK

LF_DISTATTACK_UNIQ = 2

 

Step 3: Enable distributed FTP attacks

LF_DISTFTP = 1

 

Set the following to the minimum number of unique IP addresses that trigger
LF_DISTFTP. LF_DISTFTP_UNIQ must be <= LF_DISTFTP for this to work

LF_DISTFTP_UNIQ = 3

 

If this option is set to 1 the blocks will be permanent
If this option is > 1, the blocks will be temporary for the specified number
of seconds

LF_DISTFTP_PERM =1

 

Step 4: Enable distributed SMTP attacks.

 

LF_DISTSMTP =1

 

Set the following to the minimum number of unique IP addresses that trigger
LF_DISTSMTP. LF_DISTSMTP_UNIQ must be <= LF_DISTSMTP for this to work

LF_DISTSMTP_UNIQ =4

 

If this option is set to 1 the blocks will be permanent
If this option is > 1, the blocks will be temporary for the specified number
of seconds

LF_DISTSMTP_PERM =1

 

This is the interval during which a distributed FTP or SMTP attack is
measured

LF_DIST_INTERVAL = 300