DOS ATTACK PART 1

DOS INTRODUCTION
Its an attack on computer or a network which prevents legitimates use of its resources
In DOS attack ,attacker flood a victim system with non-legitimates service request or traffic
to overload its resources ,which prevents it from performing intended tasks

SYMPTOMS OF DOS ATTACK:

1. unusually slow network performance
2. Dramatic increase in the amount of spam emails received
3. Unavailability of a particular website 
4. Inability to access any website

DOS ATTACK TECHNIQUE:

• Bandwidth attack
• Service request flood
• Syn flood attack
• ICMP flood attack
• Pear to pear attack 
• Permanent DOS
• Application level flood attack
• Sending or receiving file over network(it works in network only)
• using cain and abel arp poisoning attack(for network only)

BANDWIDTH ATTACK:

• A single user cannot generate enough request to flood network equipment ;hence DDOS is used 
• Attacker use botnets to carryout DDOS
• whole bandwidth is flooded with fake requests and no bandwidth is available for legitimate users.

SERVICE REQUEST FLOOD:

• An attacker or group of zombies(bots) attempts to exhaust server resources by setting up tearing down tcp connections
• it initiates a request on every connection
• service request flood attacks flood servers with ahigh rate of connection from a valid source

SYN ATTACK:

The attack exploits the three-way handshake method

Attacker send fake TCP SYN request to the the target sever

the target machine send back the SYN ACK packet and wait for the response to complete the handshake

the target machine donot get ACK because the source address is fake


ICMP FLOODING ATTACK:
ICMP is atype of DoS attack in which a large amount of packets of fake source is send to target server in order to crash it and cause stop responding to TCP/IP requests
After the ICMP threshold is reached, the router rejects further ICMP echo requests from all the address in the same security zone for the remainder of the crrent second and next second as well