Routing Engine

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.

For a description of the Routing Engine's role in router architecture, see Routing Engine Architecture.

One or two Routing Engines can be installed into the midplane from the rear of the chassis, as shown in Figure 2. If two Routing Engines are installed, they determine together which is the master and which is in standby mode (and so performs no functions). By default, the Routing Engine in the slot labeled RE0 is the master. To change the default, include the appropriate [edit chassis redundancy routing-engine] statement in the configuration, as described in the section about Routing Engine redundancy in the JUNOS System Basics Configuration Guide.

The Routing Engine is hot-pluggable, as described in Field-Replaceable Units (FRUs). Removal or failure of the standby Routing Engine does not affect router function. If the master Routing Engine is removed from the chassis, the effect depends on whether two Routing Engines are installed:

• If there is only one Routing Engine, packet forwarding halts until a Routing Engine is installed and functioning normally.
• If there are two Routing Engines, the effect depends on the software configuration:
  • If the Routing Engines are running JUNOS Release 6.0 or later and are configured for graceful switchover, the standby Routing Engine automatically assumes mastership without interruption of forwarding performance. For information about configuring graceful switchover, see the section about Routing Engine redundancy in the JUNOS System Basics Configuration Guide.

    If the Routing Engines are configured for graceful switchover and are running a JUNOS release that supports graceful switchover, the standby Routing Engine immediately assumes Routing Engine functions and there is no interruption to packet forwarding. For information about configuring graceful switchover, see the section about Routing Engine redundancy in the JUNOS System Basics Configuration Guide.

    We recommend you run JUNOS Release 7.0 or later on the M20 router to support graceful switchover.

  • Otherwise, forwarding halts while the standby Routing Engine becomes the master and resets the Packet Forwarding Engine.

For Routing Engine replacement instructions, see Replacing a Routing Engine.

Note that the effect of a hardware or software failure on the master Routing Engine differs from the effect of removing the master Routing Engine:

• With the default router configuration, in case of failure you must correct the problem manually. You can issue the appropriate request chassis routing-engine master command to switch mastership to the other Routing Engine, for example. For information about the command, see the JUNOS System Basics and Services Command Reference.
• On routers with two installed Routing Engines, you can configure graceful switchover of Routing Engines, as previously described for the case of Routing Engine removal. When the standby Routing Engine stops receiving keepalive signals from the master Routing Engine, it automatically assumes mastership without interruption of forwarding performance.

  We recommend you run JUNOS Release 7.0 or later on the M20 router to support graceful switchover.

• On routers with two installed Routing Engines running any JUNOS release, you can configure automatic Routing Engine mastership failover. When the standby Routing Engine stops receiving keepalive signals from the master Routing Engine, it automatically assumes mastership. Packet forwarding halts while the Packet Forwarding Engine components reset and connect to the new master Routing Engine.

For information about configuring graceful switchover or automatic mastership failover, see the section about Routing Engine redundancy in the JUNOS System Basics Configuration Guide.

Routing Engine Components

The Routing Engine (shown in Figure 14) is a two-board system with the following components:

• CPU—Runs JUNOS software to maintain the router's routing tables and routing protocols. It has a Pentium-class processor.
• DRAM—Provides storage for the routing and forwarding tables and for other Routing Engine processes.
• Internal flash disk—Provides primary storage for software images, configuration files, and microcode. The drive is a fixed compact flask disk and is inaccessible from outside the router.
• Hard disk—Provides secondary storage for log files, memory dumps, and rebooting the system if the internal flash disk fails.
• PC card slots—Accept removable PC cards, which store software images for system upgrades.
• LED—Indicates disk activity for the internal IDE interface. It does not necessarily indicate routing-related activity.
• 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.

Note: The LEDs that report Routing Engine status are on the Routing Engine panel and on the craft interface, rather than the Routing Engine faceplate. For more information, see Routing Engine Panel and Fan Tray.

Note: The appearance and position of electronic components or the PC Card slot on your Routing Engine might differ from Figure 14 and other figures in this document that depict the Routing Engine. These differences do not affect Routing Engine installation and removal or functionality.

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 version.

Figure 14: Routing Engine

Routing Engine Panel and Fan Tray

The Routing Engine panel installs into the rear of the chassis, to the right of the Routing Engine slots (see Figure 2). Behind the panel are two fans for cooling the Routing Engine. As shown in Figure 15, LEDs on the left side of the panel faceplate report Routing Engine status. The upper set reports the status of the Routing Engine in the upper Routing Engine slot (RE0) and the lower set reports the status of the Routing Engine in the lower slot (RE1). Each set includes three LEDs—an amber one labeled OFFLINE, a green one labeled ONLINE, and a blue one labeled MASTER.

To the right of each MASTER LED is an offline button for the same Routing Engine as the LEDs. Press the button to take the Routing Engine offline for replacement as directed in this manual.

Figure 15: Routing Engine Panel

Table 11 describes the Routing Engine LED states.

Table 11: States for Routing Engine LEDs

LEDs and offline buttons with the same function also appear on the craft interface. For more information, see Routing Engine LEDs and Offline Buttons.