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Derek den Haas
6313b1570d
Ephemeral ports were drawn at random from the 16384-port dynamic range on every dial. Under connection-per-request churn the birthday paradox reuses a recently-released port after only a few dozen dials (~1% per dial at 200 outstanding-in-teardown), and a reused 4-tuple lands on whatever state the previous conversation left along the path, such as the peer's TIME-WAIT socket or a NAT's flow-table entry, which silently swallows the new SYN. Measured end to end: an HTTP client with keep-alives off against a macOS peer hit a dead dial after ~286 connections and stayed dark for ~30 seconds, exactly one 2MSL TIME-WAIT expiry. Allocate sequentially from a per-stack random starting offset instead: a port is only revisited after the full 16384-port cycle, and the random start keeps a rebooted node off the ports its previous life just used. TestEphemeralPortSequence pins the full-cycle-no-reuse property. Co-authored-by: Derek den Haas <d.haas@directcode.com>