Cisco 3750G - Catalyst Integrated Wireless LAN Controller, Руководство по настройке

Страница: 1076 / 1204

43-16
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 43 Troubleshooting
Using Layer 2 Traceroute
To end a ping session, enter the escape sequence ( Ctrl-^ X by default). 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 43-16
•
Usage Guidelines, page 43-16
• Displaying the Physical Path, page 43-17
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.
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.
Usage Guidelines
These are the Layer 2 traceroute usage 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.
For a list of switches that support Layer 2 traceroute, see the “Usage Guidelines” section on
page 43-16 . If any devices in the physical path are transparent to CDP, the switch cannot identify
the path through these devices. For more information about enabling CDP, see Chapter 26,
“Configuring CDP.”
• A switch is reachable from another switch when you can test connectivity by using the ping
privileged EXEC command. All switches 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 switches 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.