• You can enter the
traceroute mac
or the
traceroute mac ip
privileged EXEC command on a device
that is not in the physical path from the source device to the destination device. All devices 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 device 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 device uses the associated MAC address and
identifies the physical path.
• If an ARP entry does not exist, the device 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.
• Layer 2 traceroute opens a listening socket on the User Datagram Protocol (UDP) port 2228 that can be
accessed remotely with any IPv4 address, and does not require any authentication. This UDP socket
allows to read VLAN information, links, presence of particular MAC addresses, and CDP neighbor
information, from the device. This information can be used to eventually build a complete picture of the
Layer 2 network topology.
• Layer 2 traceroute is enabled by default and can be disabled by running the
no l2 traceroute
command
in global configuration mode. To re-enable Layer 2 traceroute, use the
l2 traceroute
command in global
configuration mode.
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 Device 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 Device is the destination of the
traceroute, it is displayed as the final destination in the traceroute output. Intermediate devices 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 Device is a multilayer Device that is routing a particular packet, this device
shows up as a hop in the traceroute output.
System Management Configuration Guide, Cisco IOS XE Fuji 16.8.x (Catalyst 9500 Switches)
269
Troubleshooting the Software Configuration
IP Traceroute
