Monitoring of traffic in an IP network is a crucial point to prevent big failures of the system and to deliver a good quality of service to end-users. This is a key factor of success for large-scale Internet Service Providers. For this reason, Telecom Italia developed a series of techniques that have been defined as Alternate Marking Performance Monitoring. The main requirements of this system are scalability, robustness, and flexibility. This work aims to develop and test a system able to perform passive network monitoring exploiting Alternate Marking techniques in a multipoint environment. Starting from several works that have been carried out in the past, critical points that have been highlighted has been addressed, proposing a solution for some of them.