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Related Documentation

Chassis Status LEDs on EX4300 Switches

An EX4300 switch has three chassis status LEDs (labeled ALM, SYS, and MST) on the right of the LCD panel, next to the Menu and Enter buttons (see Figure 13).

Figure 13: Chassis Status LEDs in an EX4300 Switch

Chassis Status
LEDs in an EX4300 Switch
LCD panel
LCD panel Menu button
LCD panel Enter button
Chassis status LEDs

Table 13 describes the chassis status LEDs on an EX4300 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 led.

Table 13: Chassis Status LEDs on an EX4300 Switch

LED Label


State and Description

ALM (Alarm)


There is no alarm or the switch is halted.


There is a major alarm.

Note: When you connect power to the switch, the Alarm (ALM) LED glows 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 Connecting a Switch 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.

Note: The Alarm (ALM) LED glows yellow 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 (Master)


In a standalone EX4300 switch:

  • On steadily—The switch is functioning normally as the master.
  • Off—The switch is powered off or is halted.

In a Virtual Chassis configuration:

  • On steadily—The switch is the master in the Virtual Chassis configuration.
  • Blinking—The switch is the backup in the Virtual Chassis configuration.
  • Off—The switch is a line card 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 (yellow) indicates a noncritical condition that requires monitoring or maintenance. A minor alarm that is left unchecked might cause interruption in service or performance degradation.

All three LEDs can be lit simultaneously.

Related Documentation

Modified: 2015-06-23