44-13
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 44 Troubleshooting
Using Layer 2 Traceroute
• Enable global IP routing, create an SVI, and assign an IP address to it. For more information about
SVIs, see the
“Switch Virtual Interfaces” section on page 9-5.
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
• Understanding Layer 2 Traceroute, page 13
• Layer 2 Traceroute Usage Guidelines, page 13
• Displaying the Physical Path, page 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
• 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 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.
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