Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


M7i Routing Engine Description


The Routing Engine runs Junos OS. The 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 Routing Engine is installed into the midplane from the front of the chassis, as shown in M7i Chassis Description. For a more detailed description of the Routing Engine's role in router architecture, see Routing Engine Architecture.

The Routing Engine is hot-pluggable; you can remove and replace the Routing Engine without powering down the router, but the routing functions of the system are interrupted when it is removed.

Figure 1: Routing Engine
Routing Engine

The Routing Engine (shown in Figure 1) is a two-board system with the following components:

  • CPU—Runs Junos OS to maintain the router's routing tables and routing protocols. It has a Pentium-class processor.

  • SDRAM—Provides storage for the routing and forwarding tables and for other Routing Engine processes.

  • CompactFlash card—This disk is optional. If installed, it provides primary storage. It can accommodate software images, configuration files, and microcode.

  • Hard disk—If no CompactFlash card is installed, provides primary storage for software images, configuration files, and microcode. If an CompactFlash card is installed, the hard disk provides secondary storage for log files and memory dumps, and can reboot the system if the CompactFlash card fails.

  • PC card slot—Accepts a removable PC card, which stores software images for system upgrades.

  • Four LEDs—A green LED labeled HDD, a blue LED labeled MASTER, a red LED labeled FAIL, and a green LED labeled ONLINE indicate Routing Engine status.

  • Interfaces for out-of-band management access—Provide information about Routing Engine status to devices (console, laptop, or terminal server) that can be attached to access ports located on the Routing Engine.

  • I2C/EEPROM—Stores the serial number of the Routing Engine.

  • Reset button—Reboots the Routing Engine when pressed.

  • Offline button—Powers down the Routing Engine when pressed.

  • Thumbscrews—Secure the Routing Engine in the chassis.

Boot Sequence

The disk from which the router boots is called the primary boot device, and the other disk is the alternate boot device.

The router attempts to boot from three devices in this order:

  • PC Card

  • CompactFlash card

  • Hard disk


If the router boots from an alternate boot device, a yellow alarm lights the LED on the router’s craft interface.

M7i Routing Engine Management Ports

On the right half of the Routing Engine are ports for connecting the Routing Engine to one or more external devices on which system administrators can issue Junos OS command-line interface (CLI) commands to manage the router.

The ports are labeled and function as follows:

  • CONSOLE—Connects the Routing Engine to a system console through an RS-232 (EIA-232) serial cable.

  • AUX/MODEM— Connects the Routing Engine to a laptop, modem, or other auxiliary device through an RS-232 (EIA-232) serial cable.

  • MGMT—Connects the Routing Engine through an Ethernet connection to a management LAN (or any other device that plugs into an Ethernet connection) for out-of-band management. The port uses an autosensing RJ-45 connector to support both 10- and 100-Mbps connections. Two small LEDs on the left edge of the port indicate the connection in use: the yellow LED lights for a 10-Mbps connection and the green LED lights for a 100-Mbps connection.

For information about the pinouts for the connectors, see RJ-45 Connector Pinouts for the M7i Routing Engine MGMT Port.

Figure 2 shows the ports that connect to the Routing Engine.

Figure 2: Routing Engine Interface Ports
Routing Engine Interface Ports