Mx480 Component Redundancy - Juniper MX480 Hardware Manual

MX480 Universal Routing Platform Hardware Guide

MX480 Component Redundancy

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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 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 Administration Library.
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
(left to right). Each AC power supply provides power to all components in the
PEM3
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.
PEM0 through
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