Infrastructure · Topic 1 of 5
Status Lights on Cisco Devices
Learn to read the link and system status lights on a Cisco switch or router, what green, amber, solid and blinking mean, and how to report them.
- 4 min
- Green usually means good, and amber usually means a problem or a port that is not forwarding.
- Solid green on a port means the link is up. Blinking green means traffic is passing.
- An off port light means no link, no cable or a shutdown port.
What it is
Status lights are small LEDs on a device that show at a glance whether it is working.
A Cisco switch has a light for each port and a few lights for the whole unit. Routers and access points have a similar set.
A support technician is often asked to look at the lights and report what they see. An engineer then uses that report to decide what is wrong, so you need to describe the colour and the pattern clearly.
How it works
Each light has a colour and a pattern, and together they give the meaning.
Colours and patterns
The colours are usually green and amber. The pattern is one of three kinds.
- Off means no light at all.
- Solid means the light stays on and does not change.
- Blinking means the light flashes on and off. Alternating means it switches between two colours.
Port lights on a switch
Each port normally has one light. A typical Catalyst switch uses the following meanings.
| Light | Usual meaning |
|---|---|
| Off | No link, nothing plugged in, or the port is shut down |
| Solid green | Link is up, and the device at the other end is detected |
| Blinking green | The port is sending or receiving traffic |
| Alternating green and amber | A link fault, such as many errors on the link |
| Solid amber | The port is blocked and not forwarding traffic, for example by spanning tree |
After a cable is plugged in, a port may show amber for a short time before it turns green. This is normal, because the switch checks for loops before it forwards traffic, and with classic spanning tree that check can take about half a minute.
The exact meanings can change between models. The hardware guide for the switch is the final word, and an engineer will tell you which meaning applies.
System and other lights
The system light, often labelled SYST or SYS, shows the health of the whole device.
| System light | Usual meaning |
|---|---|
| Off | No power |
| Green | Working normally |
| Amber | A fault or problem has been found |
Other lights show power status, whether a redundant power supply is present, and the state of PoE. A small Mode button on many Catalyst switches changes what the port lights show, for example link status, speed, duplex or PoE.
Using the lights to troubleshoot
When an engineer asks for the status, follow a simple routine.
- Say which device and which port you are looking at.
- State the colour, then say whether it is solid, blinking or alternating.
- Say whether the light on the other end of the cable matches.
An off light on both ends of a cable points to the cable, the port or a shutdown port. A green light on one end and off on the other is also worth reporting.
The lights only show the link. A green light does not prove that the device has the right IP address or VLAN.
What to remember for the exam
Six facts cover most questions on this topic.
- Green usually means good, and amber usually means a problem or a port that is not forwarding.
- Solid green on a port means the link is up. Blinking green means traffic is passing.
- An off port light means no link, no cable or a shutdown port.
- Alternating green and amber points to a link fault.
- The system light is green when the device is working normally and amber when a fault is found.
- Describe a light by its colour and by whether it is solid or blinking.
Say the colour first and the pattern second, for example "blinking green". That is the clearest way to report a light to an engineer.
Common mistakes
These four errors appear again and again.
Assuming amber always means broken. Amber can be normal for a short time after a port comes up.
Treating a green light as proof that all is well. The link is up, but the address or VLAN setting could still be wrong.
Ignoring the other end of the cable. Compare the light on both devices.
Reading the lights from memory. Models differ, so check the guide or follow the engineer's instruction.
Do not unplug or reset a device just because a light is amber. Report the light first and wait for the engineer's instruction.
Check yourself
Work through these three questions.
What does a blinking green port light normally show?
It shows that the link is up and traffic is being sent or received.
A port light is off and the cable is plugged in at both ends. What could this mean?
It could mean no link, a bad cable or port, or a port that has been shut down.
How should you describe a light to an engineer?
Give the device and port, the colour, and whether it is solid, blinking or alternating.
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