M320 Control Board (CB) Description

Each CB works with an adjacent Routing Engine to provide control and monitoring functions for the router (see Figure 1). These functions include determining Routing Engine mastership, controlling power and reset for the other router components, monitoring and controlling fan speed, and monitoring system status.

You can install one or two CBs in the router. They install into the upper rear of the chassis in the slots labeled CB0 and CB1 (referred to as CB-0 and CB-1, top to bottom) (referred to as CB-0 and CB-1, top to bottom). If two CBs are installed, one functions as the master CB and the other as its backup. If the master fails or is removed, the backup restarts and becomes the master.

Each CB requires a Routing Engine to be installed in the adjacent slot. CB0 installs above RE0, and CB1 installs below RE1. A CB cannot function if a Routing Engine is not present in the adjacent slot.

CBs are hot-pluggable.

Figure 1: CB

Each CB consists of the following components:

• PCI bus—Provides the interface to the Routing Engine.
• 1000Base-T Ethernet controller—Provides a 1-Gbps link between the Routing Engine and the on-board Fast Ethernet switch.
• Fast Ethernet switch—Provides a 100-Mbps Ethernet link to each FPC for Routing Engine data transfers.
• Three LEDs, located on the CB faceplate, indicate the status of the CB. M320 Control Board (CB) LEDs describes the functions of the CB LEDs.
• CB online/offline button, located on the CB faceplate.

  Note: When the adjacent Routing Engine is online, the online/offline button on the CB faceplate is nonfunctional. For more information, see Taking the M320 Host Subsystem Offline.

• Circuits that control fans and other hardware components in the chassis.
• Internally-generated 19.44-MHz Stratum 3 reference clock for line timing.
• Two RJ-48 connectors for external clock inputs for 19.44-MHz Stratum 3 reference clocks.

  Note: For more information about configuring an interface transmit clock, see the Junos OS Network Interfaces Configuration Guide.

• Power circuits for the Routing Engine.