Anti ddos Linux

Anti ddos Linux

DDoS protection is a big part of a sysadmins job these days, especially on big forums/hosts.
Obviously, the best plan would be to buy another server, set up a CISCO firewall on it and reroute all traffic to main server. Unfortunately, this would require funds for another dedicated server.

So, the only solution that would work right now is using the box itself as a firewall,this tutorial is for cpanel.

First things first, we make sure that everything is up to date.

Code:

yum update && yum upgrade

Ok, time to install a decent firewall. Because this server is running cPanel, we may as well use a firewall that integrates into cPanel. This is just to allow for easy configuration, CSF is great so we shall be installing that.

Code:

wget http://www.configserver.com/free/csf.tgz
tar -xzvf csf.tgz
cd csf
sh install.sh

Simple as that! Now we need to configure the firewall. Log into http://IP:2086 in an internet browser using your root username and password. Click ConfigServer Security&Firewall under Plugins. Click Firewall configuration.

Code:

Change testing to 0
SYN_FLOOD = 1
PORTFLOOD = 80
DENY_TEMP_IP_LIMIT  = 100000

And click 'change'. Restart csf+lfd then return. Next go to firewall security level. Click High then restart csf+lfd.

Next, we need some extra firewall rules to filter the common packets found in DDoS attacks. We will also limit the number of connections allowed to the server.

Code:

echo 1 > /proc/sys/net/ipv4/tcp_syncookies
iptables -A INPUT -p tcp --syn --dport 80 -d ! 127.0.0.1 -m connlimit --connlimit-above 100 -j REJECT --reject-with tcp-reset
iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP
iptables -A INPUT -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP
iptables -A INPUT -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
iptables -A INPUT -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
iptables -A INPUT -p tcp --tcp-flags ACK,FIN FIN -j DROP
iptables -A INPUT -p tcp --tcp-flags ACK,PSH PSH -j DROP
iptables -A INPUT -p tcp --tcp-flags ACK,URG URG -j DROP
iptables -A INPUT -m state --state INVALID -j DROP
iptables -A OUTPUT -m state --state INVALID -j DROP
iptables -A FORWARD -m state --state INVALID -j DROP

iptables -N syn-flood
iptables -A syn-flood -m limit --limit 1/second --limit-burst 4 -j RETURN
iptables -A syn-flood -j DROP

iptables -N udp-flood
iptables -A udp-flood -m limit --limit 4/second --limit-burst 4 -j RETURN
iptables -A udp-flood -j DROP

iptables -A INPUT -i eth0 -p tcp --tcp-flags  SYN,RST,ACK,FIN SYN,ACK -j syn-flood # SYN flood
iptables -A INPUT -i eth0 -p tcp ! --syn -m state --state NEW -j DROP
iptables -A INPUT -i eth0 -p udp -j udp-flood
iptables -A INPUT -i eth0 -f -j DROP
service iptables save

next, we will install some connection based IP banning. There is some software called ddos_deflate that we are going to use.
Download ddos_deflate.

Code:

wget http://www.inetbase.com/scripts/ddos/install.sh
sh install.sh

Great, that's installed. Now we need to change some settings.

Code:

nano /usr/local/ddos/ddos.conf

And set these vars:

Code:

* NO_OF_CONNECTIONS=100
    * EMAIL_TO="herp@derp.com"
    * BAN_PERIOD=12000
    * APF_BAN=0

Save the file and exit. Next we need to modify ddos_deflate to work with CSF.

Code:

nano /usr/local/ddos/ddos.sh

On line 138 there should be this text

Code:

$IPT -I INPUT -s $CURR_LINE_IP -j DROP

Change that line to

Code:

csf -d $CURR_LINE_IP

Save the file and exit. Next we need to modify ddos_deflate to work with CSF.

Code:

cp -s /usr/local/ddos/ddos.sh /usr/local/sbin/ddos

I have also a mod of ddos_deflate to work with SYN packets. There was once a program called syn_deflate that was exactly this, however the script was stopped being made avaliable and was lost forever!

Code:

mkdir /usr/local/synd
nano /usr/local/synd/synd.conf

The contents of synd.conf:

Code:

##### Paths of the script and other files
PROGDIR="/usr/local/synd"
PROG="/usr/local/synd/synd.sh"
IGNORE_IP_LIST="/usr/local/synd/ignore.ip.list"
CRON="/etc/cron.d/synd.cron"
APF="/etc/apf/apf"
IPT="/sbin/iptables"
##### frequency in minutes for running the script
##### Caution: Every time this setting is changed, run the script with --cron
#####          option so that the new frequency takes effect
FREQ=1

##### How many connections define a bad IP? Indicate that below.
NO_OF_CONNECTIONS=10

##### APF_BAN=1 (Make sure your APF version is atleast 0.96)
##### APF_BAN=0 (Uses iptables for banning ips instead of APF)
APF_BAN=0

##### KILL=0 (Bad IPs are'nt banned, good for interactive execution of script)
##### KILL=1 (Recommended setting)
KILL=1

##### An email is sent to the following address when an IP is banned.
##### Blank would suppress sending of mails
EMAIL_TO="herp@derp.com"

##### Number of seconds the banned ip should remain in blacklist.
BAN_PERIOD=12000

Next

Code:

nano /usr/local/synd/ignore.ip.list

Code:

127.0.0.1
external.ip.address

Code:

nano /usr/local/synd/synd.sh

Code:

#!/bin/sh
load_conf()
{
    CONF="/usr/local/synd/synd.conf"
    if [ -f "$CONF" ] && [ ! "$CONF" ==    "" ]; then
        source $CONF
    else
        head
        echo "\$CONF not found."
        exit 1
    fi
}

head()
{
    echo "Syn-Deflate"
    echo "Based on DoS-Deflate"
    echo
}

showhelp()
{
    head
    echo 'Usage: synd.sh [OPTIONS] [N]'
    echo 'N : number of SYN_RECV connections (default 10)'
    echo 'OPTIONS:'
    echo '-h | --help: Show    this help screen'
    echo '-c | --cron: Create cron job to run this script regularly (default 1 mins)'
    echo '-k | --kill: Block the offending ip making more than N SYN_RECV connections'
}

unbanip()

Next:

Code:

chmod 0755 /usr/local/synd/synd.sh
cp -s /usr/local/synd/synd.sh /usr/local/sbin/synd
/usr/local/synd/synd.sh --cron > /dev/null 2>&1

And we are all done! The server now has some pretty intense DDoS protection now!