Use the traceroute mac ip privileged EXEC command to display the Layer 2 path taken by the packets from the specified source IP address or hostname to the specified destination IP address or hostname.
traceroute mac ip {source-ip-address | source-hostname} {destination-ip-address | destination-hostname} [detail]
Syntax Description
For Layer 2 traceroute to function properly, Cisco Discovery Protocol (CDP) must be enabled on all the switches in the network. Do not disable CDP.
When the switch detects an device in the Layer 2 path that does not support Layer 2 traceroute, the switch continues to send Layer 2 trace queries and lets them time out.
The maximum number of hops identified in the path is ten.
The traceroute mac ip command output shows the Layer 2 path when the specified source and destination IP addresses are in the same subnet. When you specify the IP addresses, the switch 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 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. The IP addresses must be in the same subnet. If the IP address is not resolved, the path is not identified, and an error message appears.
The Layer 2 traceroute feature is not supported when multiple devices are attached to one port through hubs (for example, multiple CDP neighbors are detected on a port). 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.
Examples
This example shows how to display the Layer 2 path by specifying the source and destination IP addresses and by using the detail keyword:
Switch# traceroute mac ip 2.2.66.66 2.2.22.22 detail
Translating IP to mac .....
2.2.66.66 => 0000.0201.0601
2.2.22.22 => 0000.0201.0201
Source 0000.0201.0601 found on con6[WS-C2950G-24-EI] (2.2.6.6)
con6 / WS-2960-12T / 2.2.6.6 :
Gi0/1 [auto, auto] => Gi0/3 [auto, auto]
con5 / WS-C2950G-24-EI / 2.2.5.5 :
Fa0/3 [auto, auto] => Gi0/1 [auto, auto]
con1 / WS-C3550-12G / 2.2.1.1 :
Gi0/1 [auto, auto] => Gi0/2 [auto, auto]
con2 / WS-C3550-24 / 2.2.2.2 :
Gi0/2 [auto, auto] => Fa0/1 [auto, auto]
Destination 0000.0201.0201 found on con2[WS-C3550-24] (2.2.2.2)
Layer 2 trace completed.
This example shows how to display the Layer 2 path by specifying the source and destination hostnames:
Switch# traceroute mac ip con6 con2
Translating IP to mac .....
2.2.66.66 => 0000.0201.0601
2.2.22.22 => 0000.0201.0201
Source 0000.0201.0601 found on con6
con6 (2.2.6.6) :Gi0/1 => Gi0/3
con5 (2.2.5.5 ) : Gi0/3 => Gi0/1
con1 (2.2.1.1 ) : Gi0/1 => Gi0/2
con2 (2.2.2.2 ) : Gi0/2 => Fa0/1
Destination 0000.0201.0201 found on con2
Layer 2 trace completed
This example shows the Layer 2 path when ARP cannot associate the source IP address with the corresponding MAC address:
Switch# traceroute mac ip 2.2.66.66 2.2.77.77
Arp failed for destination 2.2.77.77.
Layer2 trace aborted.
