ping

ping sends ICMP Echo Requests and reports observed replies. It tests one control-message path to an address; it does not prove that TCP, UDP, DNS, authentication, or an application works.

Running a Bounded Test

Send three IPv4 requests with a two-second per-packet timeout on common iputils implementations:

$ ping -4 -c 3 -W 2 example.com

Use -6 to select IPv6. Record the resolved address because a hostname can return several addresses and repeated runs can choose differently.

Sequence and Loss

icmp_seq identifies requests within the run. Missing replies contribute to observed loss, while out-of-order replies can reflect varying delay. Small samples are noisy; compare multiple bounded intervals and the application's own error rate.

Loss can occur in either direction, and ICMP rate limiting can make ping loss differ from application loss.

Round-Trip Time

The time field is round-trip time in milliseconds from sending the request to receiving its reply. It combines outbound delay, remote processing, and return delay. It cannot reveal one-way latency without synchronized endpoint measurements.

TTL or Hop Limit

The displayed IPv4 TTL or IPv6 Hop Limit is the value remaining in the received reply. Without knowing the sender's initial value and return route, subtracting it does not yield an exact hop count. A change can reflect a different responder, initial value, or return path.

Testing the Right Layer

If ping succeeds but a service fails, test the actual port, TLS, protocol, and request. If ping fails, inspect name resolution, ip route get, neighbor state, firewall policy, and captures before declaring the host down.

Summary

You can now use ping as a bounded ICMP measurement with explicit limits.

1. Select the address family and record the resolved address.
2. Bound count and wait time for repeatable tests.
3. Interpret loss without assuming its direction or cause.
4. Treat RTT as two-way and TTL as a remaining value.
5. Test the real application separately.