Disabled Port Caused by False Link-Up If a Cisco powered device is connected to a port and you configure the port by using the power inline never interface configuration command, a false link-up can occur, placing the port into an error-disabled state. To take the port out of the error-disabled state, enter the shutdown and the no shutdown interface configuration commands. You should not connect a Cisco powered device to a port that has been configured with the power inline never command. Ping The device supports IP ping, which you can use to test connectivity to remote hosts. Ping sends an echo request packet to an address and waits for a reply. Ping returns one of these responses:
• Normal response—The normal response ( hostname is alive) occurs in 1 to 10 seconds, depending on network traffic. • Destination does not respond—If the host does not respond, a no-answer message is returned. • Unknown host—If the host does not exist, an unknown host message is returned. • Destination unreachable—If the default gateway cannot reach the specified network, a destination-unreachable message is returned. • Network or host unreachable—If there is no entry in the route table for the host or network, a network or host unreachable message is returned. Refere the section Executing Ping, on page 20 to understand how ping works.
Layer 2 Traceroute The Layer 2 traceroute feature allows the switch to identify the physical path that a packet takes from a source device to a destination device. Layer 2 traceroute supports only unicast source and destination MAC addresses. Traceroute finds the path by using the MAC address tables of the devices in the path. When the Device detects a device in the path that does not support Layer 2 traceroute, the Device continues to send Layer 2 trace queries and lets them time out. The Device can only identify the path from the source device to the destination device.
It cannot identify the path that a packet takes from source host to the source device or from the destination device to the destination host. Layer 2 Traceroute Guidelines • Cisco Discovery Protocol (CDP) must be enabled on all the devices in the network. For Layer 2 traceroute to function properly, do not disable CDP. If any devices in the physical path are transparent to CDP, the switch cannot identify the path through these devices. • A device is reachable from another device when you can test connectivity by using the ping privileged EXEC command. All devices in the physical path must be reachable from each other. • The maximum number of hops identified in the path is ten.
Troubleshooting the Software Configuration Disabled Port Caused by False Link-Up Troubleshooting the Software Configuration 3