Cisco 2950 Software Configuration Guide - Page 633
Usage Guidelines, Configuring CDP.
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Chapter 32 Troubleshooting Diagnosing Connectivity Problems 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 functional 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. Note For more information about enabling CDP, see Chapter 24, "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. • 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 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. 78-11380-10 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 32-17
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