The day my ping took countermeasures

# Summary A developer investigating an unexpected error message from the ping utility discovered that ping detects when the system clock is adjusted backward (before NTP synchronization) and responds by resetting negative round-trip time measurements to zero—a defensive mechanism the developers call "taking countermeasures." The article traces ping's history back to 1983 and examines the source code in iputils/ping/ping_common.c to explain how this error handling works and the difference between ping's legacy wall-clock mode and its newer, more accurate network timestamp mode.