Understanding the Host Subsystem

Purpose

Inspect the host subsystem to ensure that the Routing Engine and Control Board function properly.

What Is a Host Subsystem

The host subsystem provides routing and system management functions on the M320 and T320 routers and the T640 routing node. The host subsystem is comprised of two components: the Routing Engine and the Control Board. For a host subsystem to function, both of these components must be installed and operational.

The Routing Engine maintains the routing tables used by the router and controls the routing protocols that run on the router.

The Control Board provides control and monitoring functions for the router—determining Routing Engine mastership, controlling power, performing reset and SONET clocking for the other router components, monitoring and controlling fan speed, and monitoring system status using I²C controllers.

You can install one or two host subsystems on the router. You can install one or two Routing Engines. The Routing Engines install into the upper rear of the chassis in the slots labeled RE0 and RE1. If two Routing Engines are installed, one functions as master and the other acts as backup. If the master Routing Engine fails or is removed, and the backup is configured appropriately, the backup restarts and becomes master. The Routing Engines are hot-pluggable. Each Routing Engine requires that a Control Board be installed in the adjacent slot.

The Control Boards install into the upper rear of the chassis in the slots labeled CB0 and CB1. If two Control Boards are installed, one functions as master and the other acts as backup. If the master Control Board fails or is removed, the backup restarts and becomes master. The Control Boards are hot-pluggable. Each Control Board requires a Routing Engine to be installed in the adjacent slot. CB0 installs above RE0, and CB1 installs below RE1. A Control Board does not function if no Routing Engine is present in the adjacent slot.