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Routing Engines for the M120 Router

The Routing Engine is an Intel-based PCI platform that runs JUNOS Internet software. 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 Engines install into the rear of the chassis in vertical slots directly into the CB labeled CB0 and CB1. If two Routing Engines are installed, one functions as the master and the other acts as the backup. If the master Routing Engine fails or is removed, and the backup is configured appropriately, the backup takes over as the master.

If the host system is redundant, the backup Routing Engine is hot-removable and hot-insertable, but the master Routing Engine is hot-pluggable. A Routing Engine that is not redundant is hot-pluggable. Each Routing Engine requires a CB to be installed in the adjacent slot. RE0 installs below CB0, and RE1 installs below CB1. A Routing Engine does not power up if it is not installed into the CB.

There is a USB memory device that connects directly into the front of RE. The USB port allows you to plug in a USB keychain device.

Figure 16: Routing Engine

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Routing Engine Components

Each Routing Engine (shown in Figure 16) consists of the following components:

Figure 17: USB Memory Device in a Routing Engine

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Each Routing Engine has one LED that indicates its status. The LED, labeled ONLINE, is located directly on the faceplate of the Routing Engine. Table 5 describes the functions of the Routing Engine LED.

Table 5: Routing Engine LED








On steadily

Routing Engine is transitioning online.

Routing Engine is functioning normally.


On steadily

Routing Engine has failed.



On steadily

Hard disk is functioning normally.

Routing Engine Boot Sequence

The Routing Engine boots from the storage media in this order: the USB device, then the internal flash disk (if present), then the hard disk, then the LAN.

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

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

Note: If two Routing Engines are installed, they must both be the same hardware version.

Replacing a Routing Engine in an M120 Router

Removing a Routing Engine

The router can have one or two Routing Engines. They are located within the CB in the rear of the chassis on either side of the FEBs in the slots marked CB0 and CB1. Each Routing Engine weighs approximately 2.4 lb (1.1 kg).

To remove a Routing Engine from a CB (see Figure 18):

  1. Place an electrostatic bag or antistatic mat on a flat, stable surface.
  2. Attach an electrostatic discharge (ESD) grounding strap to your bare wrist and connect the strap to one of the ESD points on the chassis. Make sure the router is attached to a proper earth ground.
  3. Check whether the Routing Engine is functioning as the backup or as the master. If necessary, take the host subsystem offline as described in the hardware guide for your routing platform.

    Note: Router performance might change if the standby Routing Engine's configuration differs from the former master's configuration. For the most predictable performance, configure the two Routing Engines identically, except for parameters unique to a Routing Engine, such as the hostname defined at the [edit system] hierarchy level and the management interface (fxp0 or equivalent) defined at the [edit interfaces] hierarchy level.

    To configure Routing Engine-specific parameters- and still use the same configuration on both Routing Engines, include the appropriate configuration statements under the re0 and re1 statements at the [edit groups] hierarchy level and use the apply-groups statement. For instructions, see the JUNOS System Basics Configuration Guide.

  4. Press the red tabs on the ejector handles on both sides of the Routing Engine faceplate.
  5. Flip the ejector handles outward to unseat the Routing Engine.
  6. Grasp the Routing Engine by the ejector handles and slide it about halfway out of the chassis.
  7. Place one hand underneath the Routing Engine to support it and slide it completely out of the chassis.
  8. Place the Routing Engine on the antistatic mat.

    Note: To maintain proper airflow through the chassis, do not leave a CB installed in the chassis without a Routing Engine for extended periods of time. If a Routing Engine is removed, a replacement Routing Engine should be installed as soon as possible.

Figure 18: Removing a Routing Engine

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Installing a Routing Engine

To install a Routing Engine into a CB (see Figure 19):

  1. Attach an electrostatic discharge (ESD) grounding strap to your bare wrist and connect the strap to one of the ESD points on the chassis. Make sure the router is attached to a proper earth ground.
  2. Ensure the ejector handles are not in the locked position. If necessary, press the red tabs and flip the ejector handles outward.
  3. Place one hand underneath the Routing Engine to support it. With the other hand, grasp one of the ejector handles on the faceplate.
  4. Carefully align the sides of the Routing Engine with the guides inside the chassis.
  5. Slide the Routing Engine into the chassis until you feel resistance, then press the Routing Engine's faceplate until it engages the midplane connectors.
  6. Press both the ejector handles inward to seat the Routing Engine.

    The Routing Engine might require several minutes to boot.

  7. If applicable, tighten the screws on the extractor handles, using a Phillips screwdriver. Be sure to tighten the screws enough to seat the Routing Engine properly.
  8. After the Routing Engine boots, verify that it is installed correctly by checking the RE0 and RE1 LEDs on the craft interface. If the router is operational and the Routing Engine is functioning properly, the green OK LED lights steadily. If the red FAIL LED lights steadily instead, remove and install the Routing Engine again (see Removing a Routing Engine and Installing a Routing Engine). If the red FAIL LED still lights steadily, the Routing Engine is not functioning properly. Contact your customer support representative.

    To check the status of the Routing Engine, use the CLI command:

    user@host> show chassis routing-engine
    Routing Engine status:   
      Slot 0:
        Current state                 Master

    For more information about using the CLI, see the JUNOS software manuals.

Figure 19: Installing a Routing Engine

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