MX480 Component Redundancy

• Host subsystem—The host subsystem consists of a Routing Engine functioning together with an SCB. 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. To operate, each host subsystem requires a Routing Engine installed directly into in an SCB.

  If the Routing Engines are configured for graceful switchover, the backup Routing Engine automatically synchronizes its configuration and state with the master Routing Engine. Any update to the master Routing Engine state is replicated on the backup Routing Engine. If the backup Routing Engine assumes mastership, packet forwarding continues through the router without interruption. For more information about graceful switchover, see the Junos OS System Basics Configuration Guide .

• Power supplies—In the low-line (110 V) AC power configuration, the router contains three or four AC power supplies, located horizontally at the rear of the chassis in slots PEM0 through PEM3 (left to right). Each AC power supply provides power to all components in the router. When three power supplies are present, they share power almost equally within a fully populated system. Four AC power supplies provide full power redundancy. If one power supply fails or is removed, the remaining power supplies instantly assume the entire electrical load without interruption. Three power supplies provide the maximum configuration with full power for as long as the router is operational.

  In the high-line (220 V) AC power configuration, the router contains two or four AC power supplies located horizontally at the rear of the chassis in slots PEM0 through PEM3 (left to right). Each AC power supply provides power to all components in the router. When two or more power supplies are present, they share power almost equally within a fully populated system. Four AC power supplies provide full power redundancy. If one power supply fails or is removed, the remaining power supplies instantly assume the entire electrical load without interruption. Two power supplies provide the maximum configuration with full power for as long as the router is operational.

  In the DC configuration, two power supplies are required to supply power to a fully configured router. One power supply supports approximately half of the components in the router, and the other power supply supports the remaining components. The addition of two power supplies provides full power redundancy. If one power supply fails or is removed, the remaining power supplies instantly assume the entire electrical load without interruption. Two power supplies provide the maximum configuration with full power for as long as the router is operational.

• 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.