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I have stated that loopback tests do not work for synchronous
PPP connections, and neither do they work for X.25 or frame relay
connections. If, however, the type of communications you're using
allows loopbacks (such as the Cisco HDLC encapsulation), they are a
useful troubleshooting tool. On more complex internetworks, where
connections pass through many router devices, ping tests help you
identify where connectivity fails and, potentially, which link is
introducing errors in communication. To check connectivity, the
ping command
issued in nonprivileged mode sends 5 ICMP ping packets, each of 100
bytes. This is good for checking physical connectivity and ensuring
that routing tables have all the necessary entries. To use the
ping command to
check the integrity of connections, you must be in privileged mode,
which gives you options to set the size, number, and data pattern of
ping packets sent. A typical screen display for pinging in
privileged mode is given in Fig. 8-7. |
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