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Chapter 6

Troubleshooting TCP/IP Connectivity

Here is the output of the

ping

command from Router A:

Router_A>

ping 172.16.30.6

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.30.6, timeout is
2 seconds:

.....

Success rate is 0 percent (0/5)

Router_A>

Now that you have seen the output from the

ping

command, look at what

the

traceroute

command gives back as a result:

Router_A#

traceroute 172.16.50.2

Type escape sequence to abort.

Tracing the route to 172.16.50.2

1 172.16.30.6 4 msec 0 msec 4 msec

2 * * *

3 * * *

4 * ^C

Router_A#

Figure 6.5 gives more insight to what happened with the

traceroute

command. The arrows on the diagram represent the sequence and direction
in which the ICMP requests are sent. The first request is sent to Router B.
Router B responds. The third arrow indicates that the ICMP request is sent
to Router C. As you can see, there is no arrow indicating that a response is
sent to Router A. This diagram shows that the ICMP request did get to
Router C, but that a response was not sent back to Router A. This indicates
that Router C does not know how to return the response, indicating that
Router C has not learned the route to Router A, and it has lost its gateway
of last resort.

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