<span lang="en">Nowadays traffic monitoring is a must for manypurposes (IDS, antivirus, QoS monitoring, network problem detection, etc.) Deployment of high speed networks implies problems with these kind of systems to be able to cope with all the traffic in the network. Therefore, it would be interesting to know in advance whether our system will be able to do its task correctly, or it needs more processing power. This paper presents a simulator for network traffic capturing systems that use commodity hardware and general purpose operating systems. In order to establish the different elements of the simulator we carried out an in depth study of the network capturing subsystem in the Linux kernel. We identified the different stages of the travel of packets from wire to application, as well as the particular behavior of the system and computational cost for each one of them. With this information we have built up a model that simulates these different stages of a capturing system. This model allows us to estimate the performance a network application will be able to achieve, when packet losses will start and where they will appear.</span>