January 28, 2011

Denial Of Service Attack

It is is an attempt to make a computer resource unavailable to its intended users by remote users. This is one of the Botnet Attacks. It generally consists of the concerted efforts of a person or people to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely. Creators who use make or program this attack will target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even root nameservers.  



One common method of attack involves saturating the target machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.

Symptoms:


symptoms of denial-of-service attacks to include:
  • Unusually slow network performance like opening files or accessing web sites
  • Unavailability of a particular web site
  • Inability to access any web site
  • Dramatic increase in the number of spam emails received
Denial-of-service attacks can also lead to problems in the network 'branches' around the actual computer being attacked. If the attack conducted on a sufficiently large scale, entire geographical regions of Internet connectivity can be compromised without the attacker's knowledge or intent by incorrectly configured or flimsy network infrastructure equipment.

Methods of Attack: 

A "denial-of-service" attack is characterized by an explicit attempt by attackers to prevent legitimate users of a service from using that service. There are two general forms of DoS attacks: those that crash services and those that flood services. Attacks can be directed at any network device, including attacks on routing devices and web, electronic mail, or Domain Name System servers.

A DoS attack can be perpetrated in a number of ways. The five basic types of attack are:
  1. Consumption of computational resources, such as bandwidth, disk space, or processor time.
  2. Disruption of configuration information, such as routing information.
  3. Disruption of state information, such as unsolicited resetting of TCP sessions.
  4. Disruption of physical network components.
  5. Obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.
A DoS attack may include execution of malware intended to:
  • Max out the processor's usage, preventing any work from occurring.
  • Trigger errors in the microcode of the machine.
  • Trigger errors in the sequencing of instructions, so as to force the computer into an unstable state or lock-up.
  • Exploit errors in the operating system, causing resource starvation and/or thrashing, i.e. to use up all available facilities so no real work can be accomplished.
  • Crash the operating system itself.
 

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