Executing Ip Traceroute - Cisco Catalyst 3750 Software Configuration Manual

Using IP Traceroute
of 1 or 0, it drops the datagram and sends back an Internet Control Message Protocol (ICMP)
time-to-live-exceeded message to the sender. Traceroute determines the address of the first hop by
examining the source address field of the ICMP time-to-live-exceeded message.
To identify the next hop, traceroute sends a UDP packet with a TTL value of 2. The first router
decrements the TTL field by 1 and sends the datagram to the next router. The second router sees a TTL
value of 1, discards the datagram, and returns the time-to-live-exceeded message to the source. This
process continues until the TTL is incremented to a value large enough for the datagram to reach the
destination host (or until the maximum TTL is reached).
To determine when a datagram reaches its destination, traceroute sets the UDP destination port number
in the datagram to a very large value that the destination host is unlikely to be using. When a host
receives a datagram destined to itself containing a destination port number that is unused locally, it sends
an ICMP port unreachable error to the source. Because all errors except port unreachable errors come
from intermediate hops, the receipt of a port unreachable error means this message was sent by the
destination.

Executing IP Traceroute

Beginning in privileged EXEC mode, follow this step to trace the path packets take through the network:
Command
traceroute ip host
Note Though other protocol keywords are available with the traceroute privileged EXEC command, they are
not supported in this release.
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.
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.
Catalyst 3750 Metro Switch Software Configuration Guide
34-12
Purpose
Trace the path packets take through the network by using IP.
Chapter 34 Troubleshooting
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