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=INTRODUCTION TO DENIAL OF SERVICE=
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1)WHAT IS A DENIAL OF SERVICE ATTACK?

Denial of service is about without permission knocking off services, for example through crashing the whole  system. This kind of attacks are easy to launch and it is hard to protect a system against them. The basic  problem is that Unix assumes that users on the system or on other systems will be well behaved.

Sometimes could a denial of service attack be a part of an attack to gain access at a system. At the moment  I can think of these reasons and specific holes:

1. Some older X-lock versions could be crashed with a method from the denial of service family leaving the  system open. Physical access was needed to use the work space after.

2. Syn flooding could be a part of a IP-spoof attack method.

3. Some program systems could have holes under the startup, that could be used to gain root, for example  SSH (secure shell).

4. Under an attack it could be usable to crash other machines in the network or to deny certain persons the  ability to access the system.

5. Also could a system being booted sometimes be subverted, especially rarp-boots. If we know which port  the machine listen to (69 could be a good guess) under the boot we can send false packets to it and  almost totally control the boot.