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MX104 Host Subsystem

MX104 Routing Engine Overview

The Routing Engine is a Freescale-based PC platform that runs Junos OS. Software processes that run on the Routing Engine maintain the routing tables, manage the routing protocols used on the router, control the router interfaces, control some chassis components, and provide the interface for system management and user access to the router.

You can install one or two Routing Engines in the router. The Routing Engine installs into the front of the chassis. Two USB ports on the Routing Engine accept a USB memory card that allows you to load Junos OS.

If two Routing Engines are installed, one functions as the primary and the other acts as the backup. If the primary Routing Engine fails or is removed and the backup is configured appropriately, the backup takes over as the primary. The backup Routing Engine is hot-insertable and hot-removable.

The MX104 router supports the Routing Engine with model number RE-MX104.

Figure 1: MX104 Routing EngineMX104 Routing Engine

MX104 Routing Engine Components

Five ports, located on the right side of the Routing Engine, connect 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 Routing Engine consists of the following components:

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

  • 4-GB DDR3 RAM (mini DIMM)—Provides storage for the routing and forwarding tables and for other Routing Engine processes.

  • 8-GB on-board NAND Flash—Provides primary storage for software images, configuration files, and microcode. The NAND flash is fixed and is inaccessible from outside the router.

  • Interface ports—Provides access to management devices.

    • AUX—Not supported.

    • CONSOLE—Connects the Routing Engine to a system console through a serial cable with an RJ-45 connector.

    • ETHERNET—Connects the Routing Engine through an Ethernet connection to a management LAN (or any other device that plugs into an Ethernet connection). The port uses an autosensing RJ-45 connector to support 10-Mbps, 100-Mbps, or 1000-Mbps connections. Two small LEDs on the right of the port indicate the connection in use: see MX104 Routing Engine LEDs.

  • Two USB ports—Provide a removable media interface through which you can install the Junos OS manually. Junos OS supports USB version 1.0.

  • Online/Offline button—Takes the Routing Engine online or offline when pressed (see MX104 Routing Engine Buttons).

  • Reset button—Reboots the Routing Engine when pressed (see MX104 Routing Engine Buttons).

  • LEDs—Indicates the status of the Routing Engine and its ports (see MX104 Routing Engine LEDs)

MX104 Routing Engine Buttons

Each Routing Engine has two push-button controls. The buttons, labeled ONLINE OFFLINE, and RESET, are located directly on the faceplate of the Routing Engine. Table 1 describes the functions of the buttons.

Table 1: MX104 Routing Engine Buttons






Press for 2 seconds.

Routing Engine transitions online when pressed.

Green ONLINE LED is on steadily.

Press for 4 seconds.

Routing Engine transitions offline when pressed.

All LEDs are off.


Press for 3 seconds.

Routing Engine reboots when pressed.

Green ONLINE LED is on steadily.

MX104 Routing Engine LEDs

Each Routing Engine has three LEDs that indicate its status. The LEDs, labeled MASTER, ONLINE, and OK/FAIL, are located directly on the faceplate of the Routing Engine. Table 2 describes the functions of the Routing Engine LEDs.

Table 2: MX104 Routing Engine LEDs







On steadily

Routing Engine is the primary.



On steadily

Routing Engine is online.


Routing Engine is booting.



On steadily

Routing Engine is functioning normally.


On steadily

Routing Engine has failed.

The management port labeled ETHERNET has a pair of LEDs that display the speed and status of the port.


The port labeled AUX is not supported.

Table 3 describes the LEDs in more detail.

Table 3: Management LEDs










1000-Mbps link is online.



100-Mbps link is online.


10-Mbps link is online.





The port is receiving data.


The port is not receiving data.

MX104 Boot Sequence

The MX104 router ships with Junos OS preinstalled and ready to be configured when the router is powered on. One eight-GB internal NAND Flash memory (da0) acts as the hard drive. Two USB ports on the front panel accept USB storage devices (usb0 and usb1) that can also function as alternative boot devices.

When the router boots, it first attempts to start the image on the USB 0 flash memory device, if present, then attempts to start the image on the USB 1 flash memory device, if present. If a USB flash memory device is not inserted into either of the two slots on the Routing Engine, or the attempt otherwise fails, the router next tries the active partition on the NAND Flash device.

MX104 Routing Engine and its Specifications

Table 4 provides the details of the Routing Engine supported by the MX104 router.

Table 4: MX104 Routing Engine

Model Number

Name in CLI Output

First Supported 32-bit Junos OS Release

First Supported 64-bit Junos OS Release

Management Ethernet Interface

Internal Ethernet Interface


Routing Engine





The specifications of the MX104 Routing Engine are as follows:

  • Processor—1.8-GHz

  • Memory—4 GB

  • Connection to PFEs—Gigabit Ethernet

  • Media—8 GB NAND Flash