https://blog.yusukeikoma.com/tags/tcp/Recent content in tcp on Ikoma's BlogHugoen-usTue, 01 Sep 2026 20:56:28 +0900https://blog.yusukeikoma.com/posts/two-small-writes-nagle-delayed-ack/Tue, 01 Sep 2026 20:56:28 +0900https://blog.yusukeikoma.com/posts/two-small-writes-nagle-delayed-ack/Send a header and a body as two small write() calls, then wait for a reply, and every round trip can stall for about 40 ms on an idle machine with an idle network. Neither Nagle’s algorithm nor delayed ACK is a bug; together they deadlock until a timer fires. This post predicts the stall, reproduces it with a 50-line script, reads it off a packet trace, and compares the four ways out.https://blog.yusukeikoma.com/posts/tcp-half-open-connection-detection/Sun, 23 Aug 2026 15:09:06 +0900https://blog.yusukeikoma.com/posts/tcp-half-open-connection-detection/TCP never tells you that the peer is gone. A reader blocks forever, a writer keeps retransmitting for a quarter of an hour, and SO_KEEPALIVE does nothing while data is unacknowledged. This post builds a one-file Linux lab with no root, climbs a ladder of mechanisms (nothing, keepalive, TCP_USER_TIMEOUT, an application heartbeat), measures how long each takes to notice, and shows where NAT and the RFCs fit in.