Cisco Catalyst 9400 System Management Configuration Manual page 433

Troubleshooting the Software Configuration
Symptom or Problem
No PoE on all ports or a group of ports.
Trouble is on all switch ports.
Nonpowered Ethernet devices cannot
establish an Ethernet link on any port,
and PoE devices do not power on.
Possible Cause and Solution
If there is a continuous, intermittent, or reoccurring alarm related to
power, replace the power supply if possible it is a field-replaceable
unit. Otherwise, replace the switch.
If the problem is on a consecutive group of ports but not all ports,
the power supply is probably not defective, and the problem could
be related to PoE regulators in the switch.
Use the show log privileged EXEC command to review alarms or
system messages that previously reported PoE conditions or status
changes.
If there are no alarms, use the show interface status command to
verify that the ports are not shut down or error-disabled. If ports are
error-disabled, use the shut and no shut interface configuration
commands to reenable the ports.
Use the show env power and show power inline privileged EXEC
commands to review the PoE status and power budget (available
PoE).
Review the running configuration to verify that power inline never
is not configured on the ports.
Connect a nonpowered Ethernet device directly to a switch port. Use
only a short patch cord. Do not use the existing distribution cables.
Enter the shut and no shut interface configuration commands, and
verify that an Ethernet link is established. If this connection is good,
use a short patch cord to connect a powered device to this port and
verify that it powers on. If the device powers on, verify that all
intermediate patch panels are correctly connected.
Disconnect all but one of the Ethernet cables from switch ports.
Using a short patch cord, connect a powered device to only one PoE
port. Verify the powered device does not require more power than
can be delivered by the switch port.
Use the show power inline privileged EXEC command to verify
that the powered device can receive power when the port is not shut
down. Alternatively, watch the powered device to verify that it
powers on.
If a powered device can power on when only one powered device is
connected to the switch, enter the shut and no shut interface
configuration commands on the remaining ports, and then reconnect
the Ethernet cables one at a time to the switch PoE ports. Use the
show interface status and show power inline privileged EXEC
commands to monitor inline power statistics and port status.
If there is still no PoE at any port, a fuse might be open in the PoE
section of the power supply. This normally produces an alarm. Check
the log again for alarms reported earlier by system messages.
System Management Configuration Guide, Cisco IOS XE Bengaluru 17.4.x (Catalyst 9400 Switches)
Scenarios to Troubleshoot Power over Ethernet (PoE)
415