Understanding LEDs on Network Switches
Published: 2024-07-08 10:50:24

Switches have LEDs for indicating power status, port status,link status, error indication, troubleshooting and performance monitoring.

The LED  colors for the switch and their corresponding status indications are as follows ;

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/tsllsiu4iohufy431irk.PNG)

To Select or change a mode, press the mode button until the desired mode is <u>highlighted</u>. When you change port modes, the meanings of the port  LED colors also change.

## RPS MODE
The RPS LED is only available on switch models that have an RPS port 
For RPS mode u will the switch will have the following lights.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/zrbb6cog5gvzkf1cijx2.PNG)

## Port LEDs and Modes
The port and module slots each has a port LED. As a group or individually, the LEDs show information about the switch and about the ports

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/7w0xx8mz4zvon5o9bati.PNG)


## Factors Leading to Power over Ethernet (PoE) Denial in Switches

1. Preventing Overload - Each port that provides PoE has a maximum power it can deliver. If the total power required by connected PoE devices exceeds the switch's power budget,providing power to additional devices could overload the switch.
2. Protecting Devices - Connecting devices to a switch that cannot provide sufficient power could damage the devices.
3. Maintaining Switch Stability - exceeding switch power consumption, could lead to overheating, performance degradation or other operational issues.
4. Compliance and safety- Adhering to the switch's power limitations ensures compliance with safety regulations and standards. Exceeding these limits could result in non-compliance with safety regulations and standards.

## STACK LED. 
The STACK LED shows the sequence of member switches in a stack. Up to eight switches can be members of a stack. The first eight port LEDs show the switch member number. For example, if you press the Mode button and select Stack, the port LED 1 blinks green. The LEDs for port 2 and 3 are solid green, as these represent the member numbers of other stack members. The other port LEDs are off because there are no more members in the stack.
If the port LEDs are green on all the switches in the stack,the stack is operating at full bandwidth. If any port LED is not green, the stack is not operating at full bandwidth.

Stacking- Stacking allows users to expand their network capacity without the hassle of managing multiple devices.


**TIP**  Some network switches have the ability to be connected to other switches and operate together as a single unit. These configurations are called "stacks", and are useful for quickly increasing the capacity of a network.

**A Stack** is a network solution composed of two or more stackable switches. Switches that are part of a stack behave as one single device.AS a result, a stacking solution shows the characteristics and functionality of a single switch, while having an increased number of ports.

Stackable switches can be added or removed from a stack as needed without affecting the overall performance of the stack. Depending on its topology, a stack can continue to transfer data even if a link or unit within the stack fails. 
This makes stacking an 
- effective, 
- flexible
- scalable solution to expand network capacity.

## Stacking Terminology.
The  **Active switch** is a switch in the stack that handles the configuration for the entire stack. When you want to manage your stack, the Active switch is the device that you connect to in-order to make changes. it also detect when switches enter or leave the stack, and upgrading outdated switches.
A **Standby switch** is a switch that will become the new Active switch if the original Active switch goes offline. In this way, a backup helps maintain the resiliency of the stack.
A  **Member** is a stackable switch that operates as an additional unit within the stack.
A **stack port** is a port on the switch that is used to communicate with other switches in the stack. Depending on the model, a switch can have either preconfigured or user-defined stack ports.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/sqix9axqsgipf6ry9jjj.PNG)

## Console LEDs
The console LEDs show which console port is in use. If you connect cable to a console port, the switch automatically uses that port for console communication.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/vmpjdy61mzs2jlvfkf8a.PNG)

## Ethernet Management Port LED.
To understand the management LED port follow the table below,

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/6lcwnl233n3ddfexdwke.PNG)

## Link Status.
Verify that both sides have link. A broken wire or a shutdown port  can cause one side to show link even though the other side does not have link.
A port LED that is on does not guarantee that the cable is fully functional. The cable might have encountered physical stress that causes it to function at a marginal level.
Examples of **physical stress** include;

1. Bending or flexing - Internal wires can be damaged when they're frequently moved or disconnected
2. Twisting or Torquing - Straining the cables when twisting or torquing can damage the connectors affecting the transmission of signals.
3. Rodent Damage - In some environments, rodents or pests may chew on cables, causing physical damage that affects their functionality.
4. Crushing or impact - Cables might get crushed under heavy equipment or suffer impacts from falling objects, leading to physical damage that affects their functionality.

    If the port LED does<u> not </u>turn on:
 

- Connect the cable from the switch to a known good device.
- Ensure that both ends of the cable are connected to the correct ports.
- Verify that both devices have power.
- Verify that you are using the correct cable type.
- Check for loose connections. Sometimes a cable appears to be seated, but is not. Disconnect the cable and then reconnect it.

## Spanning Tree loops.
STP loops can cause serious perfomance issues that look like port or interface problems.
A unidirectional link can cause loops. It occurs when the traffic sent by the switch is received by its neighbour but the traffic from one traffic from the neighbour is not received by the switch.ie data can be sent from one device to another, but the reverse path for data transmission is either unavailable or unreliable.
A broken fiber-optic cable, other cabling problems, or a port issue could cause this one-way communication.

You can enable UniDirectional Link Detection (UDLD) on the switch to help identify unidirectional link problems.

## Autonegotiation.

When I get called to a user to diagnose a network slowdown or a slow device, the first things include looking at the error statistics and the autonegotiation settings on the switches as well as the devices connected to them.
Autonegotiation - is the feature that allows a port on a switch ,router,server  or device to communicate with the device on the end of the link to determine the optimal duplex mode and speed  for the connection.