DoS Attack Mitigation

Here is a command line to run on your server if you think your server is under attack. It prints our a list of open connections to your server and sorts them by amount.

CentOS: netstat -ntu | awk ‘{print $5}’ | cut -d: -f1 | sort | uniq -c | sort -n

BSD: netstat -na |awk ‘{print $5}’ |cut -d “.” -f1,2,3,4 |sort |uniq -c |sort -n

You can also check for connections by running the following command.

netstat -plan | grep :80 | awk ‘{print $4 }’ | sort -n | uniq -c | sort

These are few step to be taken when you feel the server is under attack:

Step 1: Check the load using the command “w”.
Step 2: Check which service is utilizing maximum CPU by “nice top”.
Step 3: Check which IP is taking maximum connection by netstat -anpl|grep :80|awk {‘print $5’}|cut -d”:” -f1|sort|uniq -c|sort -n
Step 4: Then block the IP using firewall (APF or iptables “apf -d < IP>” )

You can also implement security features in your server like:

1) Install apache modules like mod_dosevasive and mod_security in your server.
2) Configure APF and IPTABLES to reduce the DDOS

3) Basic server securing steps: http://www.linuxdevcenter.com/pub/a/linux/2006/03/23/secure-your-server.html?page=1

4) Configure sysctl parameters in your server to drop attacks.

You can block the IP which is attacking your server using Ipsec from command prompt.

>> netsh ipsec static add filterlist name=myfilterlist
>> netsh ipsec static add filter filterlist=myfilterlist srcaddr=a.b.c.d dstaddr=Me
>> netsh ipsec static add filteraction name=myaction action=block
>> netsh ipsec static add policy name=mypolicy assign=yes
>> netsh ipsec static add rule name=myrule policy=mypolicy filterlist=myfilterlist filteraction=myaction