Network traffic anomalies are unusual changes in a network, so diagnosing anomalies is important for network management. Feature-based anomaly detection models (ab)normal network traffic behavior by analyzing packet header features. PCA-subspace method (Principal Component Analysis) has been verified as an efficient feature-based way in network-wide anomaly detection. Despite the powerful ability of PCA-subspace method for network-wide traffic detection, it cannot be effectively used for detection on a single link. In this paper, different from most works focusing on detection on flow-level traffic, based on observations of six traffic features for packet-level traffic, we propose a new approach B6-SVM to detect anomalies for packet-level traffic on a single link. The basic idea of B6-SVM is to diagnose anomalies in a multi-dimensional view of traffic features using Support Vector Machine (SVM). Through two-phase classification, B6-SVM can detect anomalies with high detection rate and low false alarm rate. The test results demonstrate the effectiveness and potential of our technique in diagnosing anomalies. Further, compared to previous feature-based anomaly detection approaches, B6-SVM provides a framework to automatically identify possible anomalous types. The framework of B6-SVM is generic and therefore, we expect the derived insights will be helpful for similar future research efforts.