The dominating Internet protocols, IP and TCP, allow some flexibility in implementation, including a variety of optional features. To support research and further development of these protocols, it is crucial to know about current deployment of protocol specific features and accompanying anomalies. This work is intended to reflect the current characteristics of Internet backbone traffic and point out misbehaviors and potential problems. On 20 consecutive days in April 2006 bidirectional traffic was collected on an OC-192 backbone link. The analysis of the data provides a comprehensive summary about current protocol usage including comparisons to prior studies. Furthermore, header misbehaviors and anomalies were found within almost every aspect analyzed and are discussed in detail. These observations are important information for designers of network protocols, network application and network attack detection systems.1..