|  | 10.3 | Verifying Address Configuration
| 10.3.2 | The telnet and ping commands

The telnet command is a simple command that you use to see whether you can connect to the router. If you cannot telnet to the router but you can ping the router, you know the problem lies in the upper-layer functionality at the router. At this point, you may want to reboot the router and telnet to it again. The ping command sends ICMP echo packets and is supported in both user and privileged EXEC modes. In this example, one ping timed out, as reported by the dot (.) and four were successfully received, as shown by the exclamation point (!). These are the results that may be returned by the ping test:
Character | Definition
! | successful receipt of an echo reply
. | timed out waiting for datagram reply
U | destination unreachable error
C | congestion-experienced packet
I | ping interrupted (e.g. Ctrl-Shift-6 X)
? | packet type unknown
& | packet TTL exceeded
The extended ping command is supported only from privileged EXEC mode. You can use the extended command mode of the ping command to specify the supported Internet header options. To enter the extended mode, enter ping <return>, then Y at the extended commands prompt.