TCP Keep-Alive
TCP keep-alive sends probe packets periodically while a connection is idle, detecting whether the peer is alive so half-open connections can be reclaimed promptly.
Purpose
It detects peer crashes or network failures on long-lived connections, preventing connection leaks and useless waiting.
Mechanism
After the idle timeout, a data-less ACK probe is sent; an ACK back means alive, an RST closes the connection, and silence triggers retries until the probe count runs out, at which point the connection is declared dead. Parameters: interval, probe count, timeout.
Use cases
- Liveness checks on long-lived connections
- Connection pool maintenance
- NAT keep-alive
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