dos(denial of service) attack

What is dos attack?
In computing, the dos ( denial of service ) attack is one of the most dangerous attack in cyber-attacks . Dos attack is a type of attack on a network that is designed to bring the network to its knees by flooding  It with useless traffic. Many dos attacks, such as the ping of death and teardrop attacks, exploit limitations in the TCP/IP protocols.



two general class of the attack
1)flooding attacks

⇒  Point to point  attacks: TCP/UDP/ICMP flooding,
⇒ Smurf attacks
⇒ Distributed attacks: hierarchical  structurer
2)corruption attacks
⇒Application/service specific
eg. polluting p2p systems


What is DDos attack?
In a distributed denial-of-service attack (DDoS attack), the incoming traffic flooding the victim originates from many different sources. This effectively makes it impossible to stop the attack simply by blocking a single source.



what is difference between dos and ddos?

The differences between DoS and DDoS are substantive and worth noting. In a DoS attack, a perpetrator uses a single Internet connection to either exploit a software vulnerability or flood a target with fake requests such as ping ,http  —usually in an attempt to exhaust server resources  (e.g., RAM and CPU).

On the other hand, distributed denial of service (DDoS) attacks are launched from multiple connected devices that are distributed across the Internet. These multi-person, multi-device barrages are generally harder to deflect, mostly due to the sheer volume of devices involved. Unlike single-source DoS attacks, DDoS assaults tend to target the network infrastructure in an attempt to saturate it with huge volumes of traffic.

DDoS attacks also differ in the manner of their execution. Broadly speaking, DoS attacks are launched using homebrewed scripts or DoS tools (e.g., Low Orbit Ion Canon), while DDoS attacks are launched from botnets—large clusters of connected devices (e.g., cellphones, PCs or routers) infected with malware that allows remote control by an attacker. 

Dos attack tools

  • LOIC (Low Orbit Ion Canon) LOIC is one of the most popular DOS attacking tools freely available on the Internet
  • XOIC. XOIC is another nice DOS attacking tool
  • HULK (HTTP Unbearable Load King) 
  • DDOSIM—Layer 7 DDOS Simulator
  • R-U-Dead-Yet
  • Tor's Hammer
  • PyLoris
  • OWASP DOS HTTP POST



⇒ loic tool

Can you find source of attack?

•          Hard to find BadGuy
  ⇒  Originator of attack compromised the handlers
  ⇒  Originator not active when DDOS attack occurs
•          Can try to find agents
          ⇒  Source IP address in packets is not reliable
 ⇒  Need to examine traffic at many points, modify traffic, or modify routers


•          DoS attacks increasing in frequency, severity and sophistication
  ⇒ 32% respondents detected DoS attacks (1999 CSI/FBI survey)

    ⇒    August 6, 2009, several social networking sites, including Twitter, Facebook, Livejournal, and Google blogging pages were hit by DDoS attacks

•          Aimed at Georgian blogger "Cyxymu".

   ⇒     Internet's root DNS servers  attacked on
•          Oct. 22, 2002, 9 out of 13 disabled for about an hour
Feb. 6, 2007, one of the servers crashed, two reportedly "suffered badly", while others saw "heavy traffic.




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