CISCO IOS in a Nutshell

Name

trace — command

Synopsis

trace [host]

Description

This command allows you to determine the most likely path to a specified host. It is often useful in troubleshooting, and is similar to the traceroute command on Unix systems or the tracert command on Windows systems. If you omit the hostname, you’ll be prompted for the necessary information. As with the ping command, the prompts differ depending on the mode you are in. The output from the trace command uses the special characters shown in Table 15-22.

Table 17-9. Special characters for trace output

Character	Meaning
xx msec	Round-trip time in milliseconds
*	Packet timeout
?	Unknown packet received
A	Administratively unreachable; possibly means that an access list or equivalent function on another router is blocking the packets
H	Host is unreachable
N	Network is unreachable
P	Protocol is unreachable
Q	Source quench
U	Port unreachable

Example

This example shows what happens when you use the trace command without supplying a hostname. Note that you’re prompted for many values that can’t be specified on the command line. Omitting the hostname therefore gives you more control over the command’s behavior than you would otherwise have.

Router#trace Protocol [ip]: Protocol Target IP address: 10.10.1.2 Can be hostname or network address Source address: The IP address of the interface to use Numeric display [n]: y Numeric display is not the default Timeout in seconds [3]: Seconds to wait for each probe Probe count [3]: ...