User / Privileged EXECDomain 1.0 / 3.0

ping [ip-address]

The fundamental connectivity testing tool. Ping utilizes the Internet Control Message Protocol (ICMP) to send Echo Requests to a target IP. If the target is alive and routing is functional, it replies with an ICMP Echo Reply.

Reading the Output Characters

Router# ping 8.8.8.8

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:

.!!!!

Success rate is 80 percent (4/5), round-trip min/avg/max = 1/2/4 ms

! Success. The Echo Reply was received.
. Timeout. The router waited 2 seconds but received nothing back. (Common on the first ping due to ARP resolution).
U Unreachable. A router along the path responded with an ICMP "Destination Unreachable" message, meaning it has no route to the target in its routing table.

CCNA Exam Gotchas

[!]

Extended Ping & Source Interfaces

By default, a router uses the IP address of the exit interface closest to the destination as the Source IP of the ping. If a remote router doesn't have a route back to that specific interface, the ping drops.

If you simply type ping and press Enter, the CLI enters "Extended Ping" mode. This interactive wizard allows you to manually override the Source IP (e.g., sourcing the ping from your Loopback interface) to verify comprehensive end-to- natural routing.