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Chapter 6
Troubleshooting TCP/IP Connectivity
This information indicates that there is a problem with the link between
Router A and Router B. Figure 6.2 shows that the link between the two rout-
ers is down. If only ping were used, the fact that the link between Routers A
and B was down would take much longer to isolate.
F I G U R E 6 . 2
Link failure detected by using the traceroute utility
It is important to use ping and traceroute commands in conjunction when you
troubleshoot network problems. Relying on only one of the utilities can mis-
lead you.
Although
ping
and
traceroute
are designed to provide detailed feed-
back, this doesn't always work. A perfect example is when
ping
or
traceroute
packets have been administratively denied. If the receiving host
is configured to not send a deny response,
ping
and
traceroute
indicate
that the attempt timed out. There are times when one type or the other will
be denied, but not both. Therefore, if you make sure to use both utilities, you
are more likely to get usable information.
The previous examples are only two of many. The
ping
and
traceroute
utilities may be used on Cisco routers to aid in diagnosing routing problems
as well as reachability problems.
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