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Troubleshooting
• Use the show interfaces privileged EXEC command to see if the port is in error-disabled, disabled, or
• Verify that the power supply installed in the switch meets the power requirements of your connected
• Verify that there is sufficient PoE power budget to provide power to the attached device. Use the show
• Verify the cable type. Many legacy powered devices, including older Cisco IP phones and access points
Interface Settings
Verify that the interface is not disabled or powered off. If an interface is manually shut down on either side
of the link, it does not come up until you reenable the interface. Use the show interfaces privileged EXEC
command to see if the interface is error-disabled, disabled, or shutdown on either side of the connection. If
needed, reenable the interface.
Ping End Device
Ping from the directly connected switch first, and then work your way back port by port, interface by interface,
trunk by trunk, until you find the source of the connectivity issue. Make sure that each switch can identify
the end device MAC address in its Content-Addressable Memory (CAM) table.
Switch Performance
Speed, Duplex, and Autonegotiation
If the port statistics show a large amount of alignment errors, frame check sequence (FCS), or late-collisions
errors, this might mean a speed or duplex mismatch.
A common issue with speed and duplex occurs when duplex and speed settings are mismatched between two
switches, between a switch and a router, or between the switch and a workstation or server. Mismatches can
happen when manually setting the speed and duplex or from autonegotiation issues between the two devices.
To maximize switch performance and to ensure a link, follow one of these guidelines when changing the
duplex or the speed settings.
• Let both ports autonegotiate both speed and duplex.
• Manually set the speed and duplex parameters for the interfaces on both ends of the connection.
shutdown. Reenable the port if necessary.
devices.
power inline global configuration command to check on the available PoE power budget.
that do not fully support IEEE 802.3af, might not support PoE when connected to the switch by a
crossover cable. Replace the crossover cable with a straight-through cable.
Noncompliant cabling or powered devices can cause a PoE port fault. Use only
Caution
standard-compliant cabling to connect Cisco prestandard IP Phones and wireless access
points or IEEE 802.3af-compliant devices. You must remove any cable or device that
causes a PoE fault.
Catalyst Digital Building Series Switch Hardware Installation Guide
Switch Performance
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