Cisco WS-C2980G-A Software Guide - Page 345
Using Layer 2 Traceroute, Layer 2 Traceroute Usage Guidelines, Identifying a Layer2 Path
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Chapter 20 Checking Status and Connectivity Using Layer 2 Traceroute Using Layer 2 Traceroute The Layer 2 Traceroute utility allows you to identify the physical path that a packet takes from a source to a destination. This utility determines the path by looking at the forwarding engine tables of the switches in the path. Information is displayed about all Catalyst 4500 series, Catalyst 5000 family, and Catalyst 6500 series switches that are in the path from the source to the destination. Layer 2 Traceroute Usage Guidelines This section lists the guidelines for the Layer 2 Traceroute utility: • The Layer 2 Traceroute utility works for unicast traffic only. • You must enable CDP on all of the Catalyst 4500 series, Catalyst 5000 family, and Catalyst 6500 series switches in the network. (See Chapter 21, "Configuring CDP," for information about enabling CDP.) If any devices in the path are transparent to CDP, l2trace will not be able to trace the Layer 2 path through those devices. • You can use this utility from a switch that is not in the Layer 2 path between the source and the destination; however, all of the switches in the path, including the source and destination, must be reachable from the switch. • All switches in the path must be reachable from each other. • You can trace a Layer 2 path by specifying the source and destination IP addresses (or IP aliases) or the MAC addresses. If the source and destination belong to multiple VLANs and you specify MAC addresses, you can also specify a VLAN. • The source and destination switches must belong to the same VLAN. • The maximum number of hops an l2trace query will try is 10; this includes hops involved in source tracing. • The Layer 2 Traceroute utility does not work with Token Ring VLANs, when multiple devices are attached to one port through hubs, or when multiple neighbors are on a port. Identifying a Layer 2 Path To identify a Layer 2 path, perform one of these tasks in privileged mode: Task Command Trace a Layer 2 path using MAC addresses. l2trace {src-mac-addr} {dest-mac-addr} [vlan] [detail] Trace a Layer 2 path using IP addresses or l2trace {src-ip-addr} {dest-ip-addr} [detail] IP aliases. This example shows the source and destination MAC addresses specified, with no VLAN specified but with the detail option specified. For each Catalyst 4500 series, 5000 family, and 6500 series switch found in the path, the output shows the device type, device name, device IP address, in port name, in port speed, in port duplex mode, out port name, out port speed, and out port duplex mode. 78-15486-01 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 20-11