Switch LEDs During POST

Power-On Self Test (POST) defines the series of steps that a device goes through to test the hardware and find out what is working before moving on to loading the operating system. POST processing is performed by boot code that is loaded into ROM.

Because a full operating system has not yet been loaded when the switch performs POST, it needs a way to tell the human user if POST worked well, if it failed partly, or if the switch is totally unusable. To communicate the status, the switch uses the light-emitting diodes (LEDs) on the front panel of the switch. During POST, these LEDs have one set of meanings; during normal operation, the LEDs are used for other purposes.

Figure 8-3 shows a representation of the front left part of a 2950 switch, with LEDs shown. Figure 8-3 2950 Front Panel and LEDs

RPS LED Port Status LEDs

System LED Port Mode LEDs

Mode Button

During POST, the switch varies the lights on the LEDs to imply what is happening. For instance, as do most devices, the switch starts by turning all the LEDs green for a moment, just so you can know whether the LEDs are working. On the 2950, if the system LED turns amber, the switch failed POST, meaning that it has a problem that prevents it from even bringing up the switch operating system. (Solid green on the system LED means all is well.)

RPS LED Port Status LEDs

Mode Button

The redundant power supply (RPS) LED identifies whether an RPS is installed, whether it is working, and so on. The 2950 does not have space inside the switch for an RPS, but it does allow the switch to connect to an external RPS. The LED color (green or amber), plus whether the LED is either on or flashing, tells you the status of an RPS.

Each physical port has a single LED associated with it. The meaning of those LEDs depends on which of the four port mode LEDs are lit—the stat, util, duplex, and speed LEDs. The mode button toggles the switch among the four settings, each time changing the mode from stat to util, or util to duplex, and so on. For instance, if the stat LED is on, each port LED shows a solid green light if the respective Ethernet links are working, and a flashing green when traffic is being sent across the links. If the duplex LED is lit, then the port LEDs are green if the port is using full duplex, and are not lit if using half duplex.

Table 8-2 lists the LEDs and some of their meanings. Table 8-2 2950 Switch LEDs and Meaning


Use and Meaning


OFF: Powered off GREEN: Up and working AMBER: POST failure


This signals the existence of RPS, the status of RPS, and the status of main power.

Port LEDs

Each port has a single LED, whose meaning is interpreted based on which of the four MODE leds is lit.

Mode button

When pressed, this button changes from one of four states: stat, util, duplex, and speed. The current mode is shown by the green LED beside only one of the four words stat, util, duplex, and speed.


When stat is green, each port LED shows the working status of the port. Green means functional, off means not functional, and flashing green shows link activity.


This uses the combined port LEDs to give an indication of overall switch utilization. The more port LEDs are lit, the more switch utilization is occurring.


The port LEDs show solid green if full duplex, and off if half duplex.


For 10/100 ports, the LED shows solid green if running 100 Mbps, and off if running 10 Mbps.

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