Network taps are purpose-built devices that will mirror all traffic passing between two devices such as your firewall and internet router. This is achieved by the connecting your internet router into the first port of the network tap and your firewall into the second port. The third port of the network tap is where you then attach your capture device. Most network taps operate in a failsafe method whereby if the network tap loses power it will stop mirroring the traffic to your capture device but will still pass the traffic between your firewall and internet router.