Internet of Things (IoT) has emerged these last years as one of the most attractive subjects in both the research community and the public. As a sub-domain, Wireless Sensor Networks (WSNs) have been attracting a lot of interest. However, the resource-constraint characteristics of physical objects in those networks presumably limit the design and development of security protocols. Whilst, sensor nodes usually operating in unattended and even harsh environments are prone to failures and malicious attacks. Monitoring them for attack/intrusion detection and for troubleshooting becomes thus an important issue. In this paper, we present a monitoring solution, MMT (Montimage Monitoring Tool), which enables data capture, events extraction, statistics collection, traffic analysis and reporting. The tool is applicable to 6LoWPAN-based (IPv6 over Low power Wireless Personal Area Networks) WSNs. Experiments have been performed on a real test-bed to validate and evaluate our proposition