The number of endpoints using PoE has grown significantly. PoE is an IEEE standard that delivers power to devices via an RJ45 cable, eliminating the need for a separate power cable.

This reduces the cabling needed for device connections. However, have you considered the issue of rebooting the switch causing all powered devices (PDs) to go offline? This is a major pain point for us.

The solution is Perpetual PoE.

What is Perpetual PoE?
Perpetual PoE ensures uninterrupted power to a connected PD even during switch booting, maintaining PoE power during control plane reboots.
Note: Power to the ports will be interrupted during M3 or PSE firmware upgrades, but will resume once the Cisco IOS software starts.

In addition to Perpetual POE, there is also Fast POE.

What is Fast PoE?
This feature remembers the last power drawn from a specific PSE port and restores it immediately when AC power is plugged in (within 15 to 20 seconds), without waiting for IOS to boot. With PoE-HA enabled, the switch provides power to connected PDs shortly after a power failure, even before IOS forwarding starts.
• Restores power to PD within 30 seconds of power resumption.

Note: In the case of UPOE, even if Fast PoE is available, PDs may not utilize it due to reliance on LLDP for signaling UPOE power availability, meaning PDs must wait until IOS is up and LLDP exchanges occur.

Example: Configuring Perpetual and Fast PoE
To configure Perpetual PoE on a switch:
Device> enable
Device# configure terminal
Device(config)# interface gigabitethernet2/0/1
Device(config-if)# power inline port perpetual-poe-ha
Device(config-if)# end

To configure Fast PoE on the switch:
Device> enable
Device# configure terminal
Device(config)# interface gigabitethernet2/0/1
Device(config-if)# power inline port perpetual-poe-ha
Device(config-if)# power inline port poe-ha
Device(config-if)# end

Note:-You need to shut down and then re-enable the port for the effects of Perpetual and Ft Poe to take effect, as the switch must learn the power drawn by the PD device.

Feature History for Perpetual PoE and Fast PoE
Perpetual and Fast PoE features were introduced on 9300 Switches (except for the C9300-24S and C9300-48S SKUs, which do not have the feature.) from Cisco IOS XE Everest 16.5.1a, on 9200 Cisco IOS XE Fuji 16.9.2, and from Cisco IOS XE Cupertino 17.9.1. Perpetual PoE was implemented on C9200CX-12P-2X2G, C9200CX-8P-2X2G, and C9200CX-12T-2X2G models of the Cisco Catalyst 9200CX.

Perpetual PoE is also available on 3850, 9400,9500, IE3100, and IE9300, 1200, 1300 switches.