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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter47 Troubleshooting Using IP Traceroute
•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 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 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, see the command reference for this release.
Using IP Traceroute
These sections contain this information:
•Understanding IP Traceroute, page 47-13
•Executing IP Traceroute, page 47-14

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 tracerout e ou tput .
The traceroute privileged EXEC command use s the Time To Live (TTL) fie ld i n the IP header to cause
routers and servers to generate specific return messages. Traceroute starts by sending a User Datagram
Protocol (UDP) datagram to the destination host with the TTL field set to 1. If a router finds a TTL value