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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter47 Troubleshooting
Using Layer 2 Traceroute
Using Layer 2 Traceroute
These sections contain this information:
•Understanding Layer 2 Traceroute, page 47-12
•Usage Guidelines, page 47-12
•Displaying the Physical Path, page 47-13

Understanding Layer 2 Traceroute

The Layer 2 traceroute feature allows the switch to identify the physical pa th 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 continue s to send
Layer 2 trace queries and lets them time out.
The switch can only identify the path from the source device to the destinatio n 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.

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.
For a list of switches that support Layer 2 traceroute, see the “Usage Guidelines” section on
page 47-12. 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 CD P, see Chapter 26,
“Configuring CDP.”
•A switch is reachable from another switch when you can test connec tivity by using the ping
privileged EXEC command. All switches in the physical path must be re acha ble f rom e ach oth er.
•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 th e
path must be reachable from this switch.
•The traceroute mac command output shows the Layer 2 path only when the specified source and
destination MAC addresses belong to the same VLAN. If you specify source a nd destination MAC
addresses that belong to different VLANs, the Layer 2 path is not identified, and an error message
appears.
•If you specify a multicast source or destination MAC address, the path is not identified, and an error
message appears.
•If the source or destination MAC address belongs to multiple VLANs, you must specify the VLAN
to which both the source and destination MAC addresses belong. If the VLAN is not specified, the
path is not identified, and an error message appears.