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Catalyst 3560 Switch Software Configuration Guide
OL-8553-06
Chapter 47 Troubleshooting
Using IP Traceroute
• 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.
• The traceroute mac ip command output shows the Layer 2 path when the specified source and
destination IP addresses belong to the same subnet. When you specify the IP addresses, the switch
uses the 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 MAC address
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 neighbors
are detected on a port), the Layer 2 traceroute feature is not supported. When more than one CDP
neighbor is detected on a port, the Layer 2 path is not identified, and an error message appears.
• 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, see the command reference for this release.
Using IP Traceroute
These sections contain this information:
• Understanding IP Traceroute, page 47-16
• Executing IP Traceroute, page 47-17

Understanding IP Traceroute

You can use IP traceroute to identify the path that packets take through the network on a hop-by-hop
basis. The command output displays all network layer (Layer 3) devices, such as routers, that the traffic
passes through on the way to the destination.
Your switches can participate as the source or destination of the traceroute privileged EXEC command
and might or might not appear as a hop in the traceroute command output. If the switch is the destination
of the traceroute, it is displayed as the final destination in the traceroute output. Intermediate switches
do not show up in the traceroute output if they are only bridging the packet from one port to another
within the same VLAN. However, if the intermediate switch is a multilayer switch that is routing a
particular packet, this switch shows up as a hop in the traceroute output.