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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter5 Checking Port Status an d Connectivity
Using Layer 2 Traceroute
Note For more information about enabling CDP, see Chapter19, “Understanding and Configuring
CDP.”
•All switches in the physical path must have IP connectivity. When a switch is reachable from another
switch, you can test connectivity by using the ping command in privileged EXEC mode.
•The maximum number of hops identified in the path is ten.
•You can enter the traceroute mac or the traceroute mac ip command in privileged EXEC mode on
a switch that is not in the physical path from the source device to the destination device. All switche s
in the 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 and 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.
•The traceroute mac ip command output shows the Layer 2 path whe n the specified source and
destination IP addresses belong to the same subnet. When you specify the IP addresses, the switch
uses Address Resolution Protocol (ARP) to associate the IP address with the corresponding MAC
address and the VLAN ID.
–
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 fea ture 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 appear s.
•This feature is not supported in Token Ring VLANs.
Running Layer 2 Traceroute
To display the physical path that a packet takes from a source device to a desti nation device, perform
either one of these tasks in privileged EXEC mode:
or
Command Purpose
Switch# traceroute mac {
source-mac-address
}
{
destination-mac-address
}
Runs Layer 2 traceroute to trace the path that
packets take through the network.