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Hi there, there are some tips that may and may not help you while your server is under DDoS (Distributed Denial of Service).
DDoS is attack from huge amount of IPs servers which need to overload your server and make it do not respond to request, for example to load websites etc.

Please note: I do not guarantee informations you read on this webpage are acurate and will help you although i writen the information best i could. You using all the informations provided on this page at your own risk.

When your server is under DDoS and you dont know about any firewall or limitting tool installed on server, i would try login to your server via SSH (shell, command line) i do it via Windows software called Putty.
1)
Then you may try to install software from http://deflate.medialayer.com/
It takes just a minute and this SW allow you to set limit on connections from one IP. When its reached, IP address is baned for set amount of time. After installtion you may want to edit configuration file: pico /usr/local/ddos/ddos.conf Then make changes and exit editor by shortcut Ctrl + X and save by hitting "Y" key.
This DDOS deflate SW allow you to see currently connected IPs to your server and amount of connections per IPs.
2)
Im having cPanel server and i installed Config Server Firewall, it helped decrease my server load and in cPanel it has graphical setting interface so i prefer it:
http://configserver.com/cp/csf.html This SW also have built in rules which automatically recognise bulk suspicious requests and automatically update IP ban list.
3)
You may try installing so called Mod Security ?
4)
When you loged to your server via SSH (Putty software or similar) you may try command "top -c"
It will show your server resources usage and tell you which processes or scripts use the most, maybe you find there is some issue with just one or a few files which takes high load. In this case you mamy put these files offline or whole account offline. Or you may try empty its content (backup original file before) or similar action.

If you have any other ideas or notes to my guide, please share it and help other admins at hard time during DDoS.

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Services which may help in cases of repeated attacks:
https://www.cloudflare.com/plans (there is article about CloudFlare DDoS)
http://www.koddos.com/ddos-protection.html
http://www.vistnet.com/pricing/

Hi,

DDOS attack comes on a variations. Some are on a large scale ranging from several hundred MB's to Gig's. For a start you can put a defensive mechanism on the apps side. Say, using Nginx as your web server in place of Apache. nginx can accept more connections with less resources utilized.