[MeTh0Dz]

It can it just depends. The end goal of a Denial of Service attack is too deny people service to the site or the resource. This can be done in a variety of ways. One such way is the aforementioned ping method but many servers are no longer vulnerable to this. This is usually called a ping flood or icmp flood. (Icmp packets are ping packets) The attack can also be carried out by changing routing information so that the site can't be reached, or by changing dns information. Which is many times known as dns cache poisoning. A huge influx in otherwise legal requests to a site can also crash the server, which can be perpetrated as a dos attack. There are also ways to exploit an operating system and tcp/ip to carry out such an attack. You could also feasibly carry out a dos attack using arp poisoning, although this would have to occur on a LAN.