M120 Component Redundancy

A fully configured router is designed so that no single point of failure can cause the entire system to fail. Only a fully configured router provides complete redundancy. All other configurations provide partial redundancy. The following major hardware components are redundant:

• Host subsystem—The host subsystem requires a Routing Engine to be installed directly into the CB. The router can have one or two host subsystems. If two host subsystems are installed, one functions as the master and the other functions as the backup. If the master host subsystem (or either of its components) fails, the backup can take over as the master.
• Power supplies—A router with two AC power supplies or two DC power supplies is fully power redundant. In both AC and DC configurations, the power supplies share the load almost evenly.

  Caution: Mixing AC and DC power supplies is not supported. The first power supply powered on will electrically disable the second power supply without damaging any components in the system.

• Cooling system—The cooling system has redundant components, which are controlled by the host subsystem. If one of the fans fails, the host subsystem increases the speed of the remaining fans to provide sufficient cooling for the router indefinitely.