JUNOS Internet Software Network Operations Guide: Hardware
290 ! Understanding the Host Subsystem
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 I
2
C 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.
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