Using Layer 2 Traceroute - Cisco Catalyst 3550 series Software Configuration Manual

Diagnosing Connectivity Problems
This example shows how to perform a traceroute to an IP host:
Switch# traceroute ip 171.9.15.10
Type escape sequence to abort.
Tracing the route to 171.69.115.10
1 172.2.52.1 0 msec 0 msec 4 msec
2 172.2.1.203 12 msec 8 msec 0 msec
3 171.9.16.6 4 msec 0 msec 0 msec
4 171.9.4.5 0 msec 4 msec 0 msec
5 171.9.121.34 0 msec 4 msec 4 msec
6 171.9.15.9 120 msec 132 msec 128 msec
7 171.9.15.10 132 msec 128 msec 128 msec
Switch#
The display shows the hop count, IP address of the router, and the round-trip time in milliseconds for
each of the three probes that are sent.
Table 37-2 Traceroute Output Display Characters
Character
*
?
A
H
N
P
Q
U
To terminate a trace in progress, enter the escape sequence (Ctrl-^ X by default). You enter the default
by simultaneously pressing and releasing the Ctrl, Shift, and 6 keys, and then pressing the X key.

Using Layer 2 Traceroute

This section describes this information:
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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 determines 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.
Catalyst 3550 Multilayer Switch Software Configuration Guide
37-14
Description
The probe timed out.
Unknown packet type.
Administratively unreachable. Usually, this output means that an access list is
blocking traffic.
Host unreachable.
Network unreachable.
Protocol unreachable.
Source quench.
Port unreachable.
Understanding Layer 2 Traceroute, page 37-14
Usage Guidelines, page 37-15
Displaying the Physical Path, page 37-16
Chapter 37 Troubleshooting
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