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Chapter26 Troubleshooting Using Debug Commands
•The traceroute mac ip command output shows the Layer 2 path whe n th e specified so urc e a nd
destination IP addresses belong to the same subnet. When you specify the IP a ddresse s, th e s witc h
uses Address Resolution Protocol (ARP) to associate the IP addresses with the corresponding MAC
addresses and the VLAN IDs.
–
If an ARP entry exists for the specified IP address, the switch uses the associated MA C ad dress
and identifies the physical path.
–
If an ARP entry does not exist, the switch sends an ARP query and tries to resolve the IP
address. If the IP address is not resolved, the path is not identified, and an error message
appears.
•When multiple devices are attached to one port through hubs (for example, multiple CDP neigh bors
are detected on a port), the Layer 2 traceroute feature is not supp ort ed. Wh en m ore than on e CDP
neighbor is detected on a port, the Layer 2 path is not identified, and an error message appear s.
•This feature is not supported in Token Ring VLANs.

Displaying the Physical Path

You can display physical path that a packet takes from a source device to a destination device by using
one of these privileged EXEC commands:
•tracetroute mac [interface interface-id] {source-mac-address} [interface interface-id]
{destination-mac-address} [vlan vlan-id] [detail]
•tracetroute mac ip {source-ip-address | source-hostname}{destination-ip-address |
destination-hostname} [detail]
For more information, refer to the command refer en ce f or th is re lea se.
Using Debug Commands
This section explains how you use the debug commands to diagnose and resolve internetworking
problems. It contains this information:
•Enabling Debugging on a Specific Feature, page 26-12
•Enabling All-System Diagnostics, page 26-12
•Redirecting Debug and Error Message Output, page 26-12
Caution Because debugging output is assigned high priority in the CPU process, it can render the system
unusable. For this reason, use debug commands only to troubleshoot specific proble ms or during
troubleshooting sessions with Cisco technical support staff. It is best to use debug commands during
periods of lower network traffic and fewer users. Debugging during these periods decrease s the
likelihood that increased debug command processing overhead will affect system use.
Note For complete syntax and usage information for specific debug commands, refer to the command
reference for this release.