Linux DDoS Protection

[inathan]

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.

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.

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.

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.

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.

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

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

nano /usr/local/ddos/ddos.conf
And set these vars:

* 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.

nano /usr/local/ddos/ddos.sh

On line ?138″ there should be this text

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

Change that line to

csf -d $CURR_LINE_IP

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!

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

The contents of synd.conf:

##### 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

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

127.0.0.1
external.ip.address

nano /usr/local/synd/synd.sh

#!/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()

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





Windows DDoS Protection: Optimising the TCP/IP stack

Open notepad, save the following as run.cmd
Press Y to run the tweek, then Q at the menu to disable QOS.

CLS 
@ECHO OFF 
ECHO  ------------------------------------------ 
ECHO  Type "y" to optimize Vista TCP/IP settings 
ECHO  Type "q" to disable QoS reserved bandwidth 
ECHO  Type "d" to revert to Vista default values 
ECHO  Type "n" to cancell patch and exit 
ECHO  ------------------------------------------ 
:LOOP 
SET /P choice1= Type y,n,q, or d, and press ENTER:    
IF /I "%choice1%"=="Y" GOTO TWEAK 
IF /I "%choice1%"=="Q" GOTO QOS 
IF /I "%choice1%"=="D" GOTO DEFAULT 
IF /I "%choice1%"=="N" GOTO CANCEL 
:: ELSE 
GOTO LOOP 
 
:TWEAK 
@ECHO ON 
netsh int tcp set global rss=enabled 
netsh int tcp set global chimney=enabled 
netsh int tcp set global autotuninglevel=normal 
netsh int tcp set global congestionprovider=ctcp 
netsh int tcp set global ecncapability=disabled 
netsh int tcp set global timestamps=disabled 
@ECHO OFF 
cd %temp% 
ECHO > SG_Vista_TcpIp_Patch.reg Windows Registry Editor Version 5.00   
ECHO >> SG_Vista_TcpIp_Patch.reg [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]  
ECHO >> SG_Vista_TcpIp_Patch.reg "DefaultTTL"=dword:00000040 
ECHO >> SG_Vista_TcpIp_Patch.reg "EnableTCPA"=dword:00000001 
ECHO >> SG_Vista_TcpIp_Patch.reg "Tcp1323Opts"=dword:00000001 
ECHO >> SG_Vista_TcpIp_Patch.reg "TCPMaxDataRetransmissions"=dword:00000007 
ECHO >> SG_Vista_TcpIp_Patch.reg "TCPTimedWaitDelay"=dword:0000001e 
ECHO >> SG_Vista_TcpIp_Patch.reg "SynAttackProtect"=dword:00000001 
ECHO >> SG_Vista_TcpIp_Patch.reg [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider] 
ECHO >> SG_Vista_TcpIp_Patch.reg "LocalPriority"=dword:00000004 
ECHO >> SG_Vista_TcpIp_Patch.reg "HostsPriority"=dword:00000005 
ECHO >> SG_Vista_TcpIp_Patch.reg "DnsPriority"=dword:00000006 
ECHO >> SG_Vista_TcpIp_Patch.reg "NetbtPriority"=dword:00000007 
regedit /s SG_Vista_TcpIp_Patch.reg 
del SG_Vista_TcpIp_Patch.reg 
CLS 
ECHO  * PATCH SUCCESFULLY APPLIED - PRESS ANY KEY TO EXIT * 
GOTO SUCCESS 
 
:QOS 
@ECHO OFF 
cd %temp% 
ECHO > SG_Vista_TcpIp_Patch.reg Windows Registry Editor Version 5.00   
ECHO >> SG_Vista_TcpIp_Patch.reg [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Psched]  
ECHO >> SG_Vista_TcpIp_Patch.reg "NonBestEffortLimit"=dword:00000000 
regedit /s SG_Vista_TcpIp_Patch.reg 
del SG_Vista_TcpIp_Patch.reg 
CLS 
ECHO  * QOS PATCH SUCCESFULLY APPLIED - PRESS ANY KEY TO EXIT * 
ECHO. 
ECHO  * Visit SpeedGuide.net for more broadband info and tweaks * 
ECHO. 
@PAUSE 
EXIT 
 
:DEFAULT 
@ECHO ON 
netsh int tcp set global rss=default 
netsh int tcp set global chimney=default 
netsh int tcp set global autotuninglevel=normal 
netsh int tcp set global congestionprovider=default 
netsh int tcp set global ecncapability=default 
netsh int tcp set global timestamps=default 
@ECHO OFF 
cd %temp% 
ECHO > SG_Vista_TcpIp_Default.reg Windows Registry Editor Version 5.00   
ECHO >> SG_Vista_TcpIp_Default.reg [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]  
ECHO >> SG_Vista_TcpIp_Default.reg "DefaultTTL"=- 
ECHO >> SG_Vista_TcpIp_Default.reg "EnableTCPA"=- 
ECHO >> SG_Vista_TcpIp_Default.reg "Tcp1323Opts"=dword:00000000 
ECHO >> SG_Vista_TcpIp_Default.reg "TCPMaxDataRetransmissions"=dword:000000ff 
ECHO >> SG_Vista_TcpIp_Default.reg "TCPTimedWaitDelay"=dword:ffffffff 
ECHO >> SG_Vista_TcpIp_Default.reg "SynAttackProtect"=- 
ECHO >> SG_Vista_TcpIp_Default.reg [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider] 
ECHO >> SG_Vista_TcpIp_Default.reg "LocalPriority"=dword:000001f3 
ECHO >> SG_Vista_TcpIp_Default.reg "HostsPriority"=dword:000001f4 
ECHO >> SG_Vista_TcpIp_Default.reg "DnsPriority"=dword:000007d0 
ECHO >> SG_Vista_TcpIp_Default.reg "NetbtPriority"=dword:000007d1 
ECHO >> SG_Vista_TcpIp_Default.reg [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Psched]  
ECHO >> SG_Vista_TcpIp_Default.reg "NonBestEffortLimit"=- 
regedit /s SG_Vista_TcpIp_Default.reg 
del SG_Vista_TcpIp_Default.reg 
CLS 
ECHO  * VISTA DEFAULT VALUES SUCCESFULLY APPLIED - PRESS ANY KEY TO EXIT * 
GOTO SUCCESS 
 
:SUCCESS 
netsh int tcp show global 
@PAUSE 
EXIT 
  
:CANCEL 
CLS  
ECHO   * PATCH CANCELLED BY USER - PRESS ANY KEY TO EXIT * 
@PAUSE 
EXIT

inathan Reviewed by inathan on 24th Oct 2011. Linux DDoS Protection 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. yum update && yum Rating: 5

[Tulip]

Not a bad tutorial I must say, it covers basic protection within a linux environment but you cannot beat a good old hardware firewall

[gfxguru]

nice tut+

[Krun!x]

There is no point running both CSF and ddos deflate. CSF does the same thing(CT_LIMIT).

[onel0ve]

as i know ddos deflate work with apf and its store ip into iptables or apf table .

[caloss]

Good tutorial, this will help stopping minor DDOS attacks...if you get a 1GB DDOS attack then the DC will get affected and null your IP ...Only filter service will work actually or setting up a honeypot on your network

[nba517]

nice share,is there any one shell script?