Cisco Catalyst 2960 Series, Configuration Manual

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Layer 2 Traceroute Guidelines
• Cisco Discovery Protocol (CDP) must be enabled on all the devices in the network. For Layer 2 traceroute
to function properly, do not disable CDP.
If any devices in the physical path are transparent to CDP, the switch cannot identify the path through
these devices.
• A Switch is reachable from another Switch when you can test connectivity by using the
ping
privileged
EXEC command. All Switch in the physical path must be reachable from each other.
• The maximum number of hops identified in the path is ten.
• You can enter the traceroute mac or the traceroute mac ip privileged EXEC command on a Switch
that is not in the physical path from the source device to the destination device. All Switch 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 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.
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 Switch 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 Switch do not show
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About Troubleshooting the Software Configuration