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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 42 Troubleshooting
Using Layer 2 Traceroute
To end a ping session, simultaneously press and release the Ctrl, Shift, and 6 keys, and then press the
X key.
Using Layer 2 Traceroute
These sections contain this information:
• Understanding Layer 2 Traceroute, page 42-13
• Layer 2 Traceroute Usage Guidelines, page 42-13
• Displaying the Physical Path, page 42-14
Understanding 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. It finds the path by using the MAC address tables of the switches in the path. When the
switch detects a device in the path that does not support Layer 2 traceroute, the switch continues to send
Layer 2 trace queries and lets them time out.
Note Layer 2 traceroute is available only on NNIs.
The switch 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 Usage Guidelines
These are the Layer 2 traceroute usage 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.
Note CDP is enabled by default on NNIs. You can enable CDP on ENIs, but UNIs do not support CDP.
For a list of switches that support Layer 2 traceroute, see the “Layer 2 Traceroute Usage Guidelines”
section on page 42-13. If any devices in the physical path are transparent to CDP, the switch cannot
identify the path through these devices. For more information about enabling CDP, see Chapter 23,
“Configuring CDP.”
• A switch is reachable from another switch when you can test connectivity by using the ping
privileged EXEC command. All switches in the physical path must be reachable from each other.
• The maximum number of hops identified in the path is ten.
• You can enter the traceroute mac or the traceroute mac ip privileged EXEC command on a switch
that is not in the physical path from the source device to the destination device. All switches in the
path must be reachable from this switch.
