The Routing Engine is an Intel-based PCI platform that runs JUNOS software. Software processes that run on the Routing Engine maintain the routing tables, manage the routing protocols used on the router, control the router's interfaces, control some chassis components, and provide the interface for system management and user access to the router.
The router can boot from the removable medium (PC Card or USB storage device), internal compact flash disk, or hard disk. The disk from which the router boots is called the primary boot device, and the other disk is the alternate boot device.
Note: If the router boots from an alternate boot device, a yellow alarm lights the LED on the router’s craft interface.
The router attempts to boot from three devices in this order:
Note: To reinstall the JUNOS software, you boot the router from the removable media. Do not insert the removable media during normal operations. The router does not operate normally when it is booted from the removable media.
When the router boots from the storage media (removable media, internal compact flash disk, or hard disk) it expands its search in the /config directory of the routing platform for the following files in the following order: juniper.conf (the main configuration file), rescue.conf (the rescue configuration file), and juniper.conf.1 (the first rollback configuration file). When the search finds the first configuration file that can be loaded properly, the file loads and the search ends. If none of the files can be loaded properly, the routing platform does not function properly. If the router boots from an alternate boot device, the JUNOS software displays a message indicating this when you log in to the router.