Denial of Service attacks constitutes one of the major threats, which poses immense threats to the Internet. In the present Internet has changed the way of traditional essential services such as banking, transportation and defense being operated. These operations are being replaced by cheaper, more efficient Internet-based applications. It is all because of rapid growth and success of Internet in every sector. Unfortunately with the growth of Internet, count of attacks on Internet has also increased incredibly fast. The researchers have to find details of these type of attacks because due to avoid the damaging reputation issues, In this paper, an overview of Denial-of-Service(DoS)&Distributed denial-of-service (DDOS) attacks are provided. Real distributed denial-of-service incidents with their financial impact are analyzed and finally DOS and DDOS solution is highlighted.