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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter36 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 Chapter32, “Configuring IP Unicast Routing.”
•All software versions can use a Layer 3 service policy to permit pings to and from a host con nected
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 conne cte d
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 page9-5.
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 pa th 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 continue s 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.