Write short note on Denial of Service attacks.

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written 7.4 years ago by

Denial of Service attacks (DoS) are becoming highly popular mode of web attack these days.
It involves making the computer systems inaccessible by flooding servers, networks, or even end user systems with useless traffic so that legitimate users can no longer gain access to those resources
A popular form of DoS attacks which happens worldwide is DDoS(Distributed Denial of Service) wherein multiple computer (also called zombies) participate in sending the traffic.

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DoS attacks exploit the asymmetric nature of certain types of network traffic. . Therefore DoS attacks can be classified into three categories

I. Bandwidth/Throughput Attacks:

Ping Flood attack	DDoS Attack	UDP flood attack
Saturate a network with ICMP echo requests.	Focus the internet bandwidth of many machines upon one or few machines. In this way we create a large flood effect.	Since UDP is a very simple unreliable protocol, attacker simpy creates enough packets to jam the network.

II. Protocol Attacks

Smurf attack	DNS name server attack
Here, spoofed (forged) IP packets with ICMP ECHO (ping) messages are sent with source address (forged) being the IP-address of system to be attacked.	It involves an intruder sending a large number of UDP-based DNS requests to a Nameserver using a spoofed source IP address.Any Nameserver response is sent back to the spoofed IP address as the destination

III. Software Vulnerability Attacks

Land attack	Ping of death attack	Teardrop attack
In this attack, an attacker sends spoofed TCP SYN packets, with the same source and destination addresses as the victim's host address.In some TCP/IP stack implementations those kinds of packets may cause the victim's host to crash.	It is an attempt by an attacker to crash, reboot or freeze a system by sending an illegal ICMP packet to the host under attack.The TCP/IP specification allows for a maximum packet size of up to 65536 octets. In some TCP stack implementation encountering packets of greater size may cause the victim's host to crash.	A normal packet is sent.A second packet is sent which has a fragmentation offset claiming to be inside the first fragment. This second fragment is too small to even extend outside the first fragment. This may cause an unexpected error condition to occur on the victim host

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