Understanding DDOS Attack !!!

What is DDos Attack ?


Compromised PCs, or “bots,” are formed into groups called “botnets” and are used as weapons by cyber-attackers to launch various forms of cyber attacks. These attacks range widely from DDoS to identity theft and clandestine intelligence gathering operations.
During Distributed Denial of Service attempts, attackers launch attacks using different techniques including HTTP, HTTPS, ICMP, SYN Floods, UDP Floods, DNS Request Floods, GET Floods, and others. The attack components are often used in combination, and range in size from a few hundred megabits per second (Mbps) to over 80 gigabits per second (Gbps). Increasingly sophisticated attacks are based around application requests at Layer-7.
Normally, DDOS consists of 3 parts . One is the Master ,Other the slave and atlast the victim. The master is the attack launcher ie the person/machine behind all this,sound’s COOL right . The slave is the network which is being compromised by the Master and Victim is the target site/server . Master informs the compromised machines, so called slaves to launch attack on the victim’s site/machine. Hence its also called co-ordinated attack.


How do they Do it ?


DDOS is done in 2 phases. In the first phase they try to compromise weak machines in different networks around the world. This phase is called Intrusion Phase. Its in the next phase that they install DDOS tools and starts attacking the victims machines/site. This Phase is called Distributed DoS attacks phase.

What Allowed them to Do ?

Vulnerable softwares/Applications running on a machine or network.

Open network setup.

Network/ machine setup without taking security into account.

No monitoring or DataAnalysis are being conducted.

No regular Audit / Software upgrades being conducted.

First Identify if you are really under attack. If yes, follow the below steps :

Check if your machines load is high and you have large number of HTTP process running.

To find the load just use the command w or uptime -

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Eg:

ashish@localhost>w 12:00:36 up 1 day, 20:27, 5 users, load average: 0.70, 0.70, 0.57

USER XYZ FROM LOGIN@ IDLE JCPU PCPU WHAT

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To find if there is large number of HTTP process running use the command ” ps -aux|grep HTTP|wc -l ”

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Eg:

[ashish@localhost]# ps -aux|grep HTTP|wc -l

23

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In a heavy server , the number of connection will go above 100. But during DDOS attack, the number will go even higher and thats when we need to find out from which all networks are these attacks coming. In DDOS the host machine doesn’t have much importance. Its the network which is of importance here because, an attacker will use any machine on the compromised network or even will use all the machines in the network. Hence network address is of importance while fighting with the attack.

However, there are some actions you can take to protect yourself. Here's some basic advice:

Ensure that you have adequate bandwidth on your Internet connection. You'll be able to foil many low-scale DDoS attacks by simply having enough bandwidth (and processing power) to service the requests.

Deploy an intrusion prevention system on your network. Some (but definitely not all) DDoS attacks have recognizable signatures that an IPS can detect and use to prevent the requests from reaching the Web server.

Use a DDoS prevention appliance, including any of the Cisco Systems Inc. Cisco Guard products, that is specifically designed to identify and thwart distributed denial-of-service attacks.

Maintain a backup Internet connection with a separate pool of IP addresses for critical users. While you won't be able to switch all access to your website over to a backup connection (the attacks will switch at the same time!), you can provide critical users with an alternate path to your site if the primary circuit is swamped with bogus requests.

These tips should get you started on the road toward building a hardy Web infrastructure with the highest probability of surviving a DDoS attack. Good luck!