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36-13
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
78-17058-01
Chapter 36 Troubleshooting
Using Layer 2 Traceroute
Summary
Keep these guidelines in mind while pinging:
• IP routing is available only with the metro IP access image and is disabled by default.
• To ping a host in a different IP subnetwork from the switch, you must have IP routing configured to
route between the subnets, and a static route to the destination might also be appropriate. If you need
to enable or configure IP routing, see Chapter 32, “Configuring IP Unicast Routing.”
• All software versions can use a Layer 3 service policy to permit pings to and from a host connected
to a UNI. For more information about policy maps, see the “Input and Output Policies” section on
page 30-4.
If your switch is running the metro IP access image, use one of these methods to ping a host connected
to a UNI:
• Use a Layer 3 service policy to permit pings to and from a host connected to a UNI.
• Enable global IP routing and configure a port as a routed port by using the no switchport interface
configuration command.
• Enable global IP routing, create an SVI, and assign an IP address to it. For more information about
SVIs, see the “Switch Virtual Interfaces” section on page 9-5.
To end a ping session, simultaneously press and release the Ctrl, Shift, and 6 keys, and then press the
X key.
Using Layer 2 Traceroute
These sections contain this information:
• Understanding Layer 2 Traceroute, page 36-13
• Layer 2 Traceroute Usage Guidelines, page 36-14
• Displaying the Physical Path, page 36-15
Understanding Layer 2 Traceroute
The Layer 2 traceroute feature allows the switch to identify the physical path that a packet takes from a
source device to a destination device. Layer 2 traceroute supports only unicast source and destination
MAC addresses. It finds the path by using the MAC address tables of the switches in the path. When the
switch detects a device in the path that does not support Layer 2 traceroute, the switch continues to send
Layer 2 trace queries and lets them time out.
Note Layer 2 traceroute is available only on NNIs.
The switch can only identify the path from the source device to the destination device. It cannot identify
the path that a packet takes from source host to the source device or from the destination device to the
destination host.