Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

M320 RE-A-1800 Routing Engine Description


Routing Engine Components

Each Routing Engine (shown in Figure 1 and Figure 2) consists of the following components:

  • CPU—Runs Junos OS to maintain the router's routing tables and routing protocols.

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

  • USB port—Provides a removable media interface through which you can install the Junos OS manually. See Figure 3. Junos supports USB version 1.0.

  • CompactFlash card—Provides primary storage for software images, configuration files, and microcode. The disk is a fixed compact flash and is inaccessible from outside the router.

  • SSD—Provides storage for log files, memory dumps, and rebooting the system if the CompactFlash card fails.

  • LED—Indicates disk activity. It does not necessarily indicate routing-related activity.


    The LEDs that report host module status (including Routing Engine status) are on the craft interface rather than the Routing Engine faceplate.

  • Storage LED—Indicates disk activity for the solid state disk drive.

  • 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 craft interface.

    Each Routing Engine has one 10/100-Mbps Ethernet port for connecting to a management network, and two asynchronous serial ports—one for connecting to a console and one for connecting to a modem or other auxiliary device.

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

  • Reset button—Reboots the Routing Engine when pressed.

  • Offline button—Takes the Routing Engine offline when pressed.

  • Extractor clips—Control the locking system that secures the Routing Engine.

Figure 1: RE-A-1800 Routing Engine
RE-A-1800 Routing Engine
Figure 2: RE-A-1800x2 Routing Engine
RE-A-1800x2 Routing Engine

For specific information about Routing Engine components (for example, the amount of DRAM), issue the show chassis routing-engine command.

Figure 3: USB Memory Device in an Routing Engine
USB Memory Device in an Routing

Routing Engine Boot Sequence

The Routing Engine boots from the storage media in this order: the USB device, then the CompactFlash card (if present), then the two solid state drives (SSD) and then the LAN. The device from which the router boots is called the primary boot device, and the other device is the alternate boot device.


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