thinkpad:~ # ping news.bbc.co.uk
PING newswww.bbc.net.uk (220.127.116.11): 56 data bytes 64 bytes from 18.104.22.168: icmp_seq=0 ttl=60 time=0.4 ms 64 bytes from 22.214.171.124: icmp_seq=1 ttl=60 time=0.4 ms 64 bytes from 126.96.36.199: icmp_seq=2 ttl=60 time=0.6 ms — newswww.bbc.net.uk ping statistics — 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 0.4/0.4/0.6 ms
Here, you can see the machine thinkpad sending an Internet Control Message Protocol (ICMP) echo request to the machine news.bbc.co.uk. When that host receives this ICMP echo request, it sends back an ICMP echo reply to the machine thinkpad. This back and forth happens until you press Ctrl+C to stop the sequence. After ping has been interrupted, you will be told the amount of packets that were lost (not replied) and an average of the time it took for the response to come back from the machine. On a slow or noisy network, you could well see dropped packets, which is never a good thing.
The ping program and its ICMP packet tell you only if the TCP/IP stack on the remote machine is up. It is not capable of telling you how well the machine is. You should not assume that just because the remote machine is "alive" that all services are running as they should on the machine. The ping program is really used only to test network connectivity.
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