number of independent bypass switches in a single chassis, providing higher density in the equipment rack. Terminology Bypass TAP - Normal Mode: traffic flows through the network TAP before it travels through the appliance and back onto the network Bypass TAP - Bypass Mode: heartbeat packets are sent out to the in-line security appliance, once the appliance is back on-line, it will begin returning the heartbeat packets back to the TAP indicating that the appliance is ready to resume bypass TAP normal mode. The TAP will then direct the network traffic back through the in-line security appliance along with the heartbeat packets placing the appliance back in-line. Advantages Using an external bypass switch to connect an in-line appliance such as a NGFW, IPS, or DDoS has several benefits. It keeps network traffic flowing when the in-line appliance fails. It allows the in-line appliance to be removed or serviced without impacting network traffic. For example, an IPS can be taken offline to upgrades, maintenance or troubleshooting The in-line appliance can be moved from one network segment to another without impacting network traffic. Note that the latter two advantages are not provided by internal bypass-switch functionality that may be integrated within some NGFW/IPS appliances. Some bypass TAPs support multiple modes and can be used throughout the networks lifetime, ie: aggregation, regeneration/SPAN, breakout/normal. Disadvantages Bypass switches and TAPs add acquisition cost to the monitoring solution, although they may save cost in the long run by increasing network uptime. Bypass switches move the single point of failure from the in-line monitoring appliance to the bypass switch itself. This should be a net gain in reliability, because the bypass switch is a simpler device than the monitoring appliance, and because it is designed for fault-tolerance. Nevertheless, reliability is an important criterion when evaluating bypass switch solutions. Technical information Bypass switches increase network reliability through several mechanisms including passive in-line connections, link detection, and heartbeat packets. The two network ports in a bypass switch create a fully passive in-line connection that maintains traffic flow even in the absence of power. For fiber links, a normally closed optical switch creates a path for light to flow unimpeded through the device when power is absent. For copper links, micro-relays connect the two ports when power is absent. The bypass switch monitors the status of the links between its monitor ports and the in-line appliance. If a link goes