Cisco Systems ME 3400 Using Layer 2 Traceroute

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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide

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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

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.

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.