Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual page 1177

Master External Routing Engine Role
Backup External Routing Engine Role
Linecard Role
Copyright © 2010, Juniper Networks, Inc.
Chapter 44: EX8200 Virtual Chassis—Overview, Components, and Configurations
VCP links are also needed in an EX8200 Virtual Chassis to send and receive VCCP traffic
between two EX8200 switches. You must explicitly configure VCP links between two
EX8200 switches; otherwise, the switches see the link as a network link.
The function of each hardware device in a Virtual Chassis is determined by that device's
role.
The master role in an EX8200 Virtual Chassis is assigned to an XRE200 External Routing
Engine only. The XRE200 External Routing Engine in the master role:
Controls most Routing Engine functions for all switches in the Virtual Chassis.
Manages the Virtual Chassis configuration.
Provides a single point where you can view all functionality for all devices in the Virtual
Chassis.
Runs Juniper Networks Junos operating system (Junos OS).
When a single XRE200 External Routing Engine is connecting an EX8200 Virtual Chassis
and no backup external Routing Engine is configured, the single external Routing Engine
is assigned the master role. When a backup external Routing Engine is part of the Virtual
Chassis, the external Routing Engine with the most uptime functions as the master.
The function of each hardware device in a Virtual Chassis is determined by that device's
role.
The external Routing Engine that functions in the backup role:
Maintains a state of readiness to take over the master role if the master fails.
Runs Junos OS.
Synchronizes with the master, so that it is prepared to preserve routing information
and maintain network connectivity without disruption if the master external Routing
Engine becomes unavailable.
You must have two external Routing Engines in an EX8200 Virtual Chassis configuration
to have an external Routing Engine in the backup role. When a backup external Routing
Engine is part of the Virtual Chassis, the external Routing Engine with the lesser amount
of uptime functions as the backup external Routing Engine.
All EX8200 switches in an EX8200 Virtual Chassis are assigned the linecard role. Switches
in the linecard role:
Forward network traffic.
Do not run the chassis control protocols.
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