An ICMP echo reply is the unicast diagnostic message a destination host returns after receiving an ICMP echo request. Together, the request and reply enable ping to test reachability between two hosts. section 6.5 section 6.6
A successful ping uses the reply to show that:
- The destination host received the echo request and responded. section 10.1.4
- The path supports two-way communication; ping can also report round-trip time. section 6.5
- Cisco IOS displays an exclamation mark for each request that receives an echo reply. section 6.5
Cisco IOS result
PC1# ping 10.0.0.12 sends five ICMP echo requests. Output such as !!!!! and “Success rate is 100 percent (5/5)” indicates that every request received an echo reply; the reported minimum, average, and maximum values show round-trip time.
PC1# ping 10.0.0.12 #1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.0.0.12, timeout is 2 seconds: !!!!! #2 Success rate is 100 percent (5/5), round-trip min/avg/max = 3/3/4 ms #2 #1 Sends five ICMP echo requests (pings) to the specified IP address #2 Each exclamation mark indicates a successful ping.
Use the annotated Cisco IOS output to connect echo replies with success indicators and round-trip measurements. section 6.5
