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Chassis Status LEDs in EX4200 Switches

The front panel of an EX4200 switch has three LEDs on the far right side of the panel, next to the LCD panel (see Figure 1).

Figure 1: Chassis Status LEDs in an EX4200 SwitchChassis Status LEDs in an EX4200 Switch

Table 1 describes the chassis status LEDs in an EX4200 switch, their colors and states, and the status they indicate. You can view the colors of the three LEDs remotely through the CLI by issuing the operational mode command show chassis lcd.

Table 1: Chassis Status LEDs in an EX4200 Switch

LED Label


State and Description

ALM (Alarm)


There is no alarm or the switch is halted.


There is a major alarm.


When you connect power to the switch, the Alarm (ALM) LED lights red. This behavior is normal. Plugging an active Ethernet cable into the management (MGMT) port on the switch completes the network link and turns off the ALM LED. (See Connect a Device to a Network for Out-of-Band Management.)

Connecting the switch to a dedicated management console instead of a network does not affect the ALM LED. The LED remains red until the switch is connected to a network.


There is a minor alarm.


The Alarm (ALM) LED lights amber if you commit a configuration to make it active on the switch and do not also create a rescue configuration to back it up. To save the most recently committed configuration as the rescue configuration, enter the operational mode command request system configuration rescue save.

SYS (System)


  • On steadily—Junos OS for EX Series switches has been loaded on the switch.

  • Blinking—The switch is booting.

  • Off—The switch is powered off or is halted.

MST (Primary)


In a standalone EX4200 switch:

  • On steadily—The switch is functioning normally.

  • Off—The switch is powered off or is halted.

In a Virtual chassis configuration:

  • On steadily—The switch is the primary in the Virtual Chassis configuration.

  • Blinking—The switch is the backup in the Virtual Chassis configuration.

  • Off—The switch is a linecard member in the Virtual Chassis configuration or is halted.

A major alarm (red) indicates a critical error condition that requires immediate action.

A minor alarm (amber) indicates a noncritical condition that requires monitoring or maintenance. A minor alarm that is left unchecked might cause interruption in service or performance degradation.


The amber glow of the Alarm LED that indicates a minor alarm closely resembles the red glow that indicates a major alarm.

All three LEDs can be lit simultaneously.