Disabled Port Caused By False Link-Up; Ping; Layer 2 Traceroute; Layer 2 Traceroute Guidelines - Cisco Catalyst 9400 System Management Configuration Manual

Troubleshooting the Software Configuration

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
• 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
• Network or host unreachable—If there is no entry in the route table for the host or network, a network
Refere the section

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
• A device is reachable from another device when you can test connectivity by using the ping privileged
• The maximum number of hops identified in the path is ten.
network traffic.
destination-unreachable message is returned.
or host unreachable message is returned.
Executing Ping, on page 407
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.
EXEC command. All devices in the physical path must be reachable from each other.
System Management Configuration Guide, Cisco IOS XE Bengaluru 17.4.x (Catalyst 9400 Switches)
Disabled Port Caused by False Link-Up
to understand how ping works.
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