International audienceThe Internet is a network of such significance that it is now the target of many attacks. Hackers have been first targeting users, but since few years they are now also attacking the network itself. This is why several kinds of attacks have already been studied, classified and resolved. However, this is not true for Denial of Service (DoS) attacks, for which little has been done, and the only countermeasures which have been presented, are only effective for a limited time. The MetroSec project then aims at studying these badly known DoS attacks against the network. For this purpose, MetroSec relies on the use of monitoring and measurement techniques to evaluate the impact of DoS attacks, and discover how they succeed to decrease network QoS. As a first stage in this DoS attacks analysis, this paper presents a classification of DoS attacks associated with the TCP/IP suite, and compares them with some other taxonomies of the literature to help us to understand the similarities and differences in DoS attacks and the scope of the DoS problem. We do expect to get necessary information for issuing solutions for fighting DoS