Cisco (PoE) switches by default have their PoE (Power over Ethernet) enabled on every port. This article shares some of the common CLI commands to work with the PoE capabilities of a standard Cisco (PoE enabled) switch.
The #show power inline command allows you to see all the ports which are providing power. Also as can be seen by the screenshot below the output of this command displays the maximum power that each port is capable of providing as per the IEEE 802.3af standard.
The “Power (Watts)” column displays the actual power which the port is providing to the end (PD) device. This power output will normally be negotiated (via CDP) if the end device is Cisco manufactured. If the end device is not a Cisco device (i.e. Avaya, Nortel, etc.) and is therefore not capable of power negotiation (using CDP) then the Cisco switch will default to providing the maximum 15.4 Watts (as per IEEE standard).
The above output shows the “total available” power by the switch. This brings up the topic of total power budget availability. As can be seen above there is a total 360 Watts of power available. If we multiply 24 ports x 15.4 Watts the total power requirement exceeds the 360 Watts available. Therefore the total power budget has to be a consideration when thinking of purchasing/deploying a PoE switch, there may be a requirement to buy a bigger power supply or accommodate (less than full) port usage on the respective PoE switch.
The following CLI commands allow further modification of the PoE behavior on a per-port basis.
The (config-if)#power inline auto command is enabled by default.
The (config-if)#power inline never command can be used to manually turn inline power ‘off’ on the specific port. Typically if the switch port detects a loss of link it will immediately shut down the inline power.
The (config-if)#power inline delay command configures the port to delay shutting down the inline power. This can prove useful in situations where the end device has a boot sequence which implicitly flaps the link as part of the boot procedure.