CCNA 200-301 Power over Ethernet (PoE)
What is the Role of PoE?
Power over Ethernet (PoE) is a networking standard that allows a single Ethernet cable to transmit both data and electrical power to connected devices. Its primary role is to simplify network infrastructure by eliminating the need for separate power cables and outlets for devices like IP phones, wireless access points, and security cameras.
Key Benefits
- Simplified Installation: One cable for power and data.
- Cost Savings: Reduces electrical wiring costs.
- Flexibility: Place devices anywhere, not just near power outlets.
- Centralized Power: Manage power from the network switch.
Common Powered Devices (PDs)
- Wireless Access Points (WAPs)
- IP Security Cameras
- VoIP Phones
- IoT Sensors
How Does PoE Function?
A PoE-enabled switch, known as Power Sourcing Equipment (PSE), detects if a connected device is PoE-compatible. If it is, the switch sends a low-voltage signal to determine the device's power requirements (its PoE class) and then delivers the appropriate amount of DC power over the Ethernet cable along with the data.
PoE Power Classification Override
This feature, also known as PoE policing, allows a network administrator to manually set a maximum power limit (an "administrative value") on a switch port. This configured limit overrides the power level that would normally be negotiated based on the device's PoE class.
Why is this useful?
It acts as a safety mechanism. If a connected device malfunctions or is non-compliant and tries to draw more power than the manually set limit, the switch will protect itself and the network.
When a violation occurs, the switch typically shuts down the port and places it in an err-disabled state, logging the event for the administrator. This prevents the faulty device from damaging the switch or consuming excessive power from the switch's power budget.
