TCP Ruled for 40 Years. Why Did HTTP/3 “Dump” It?

Sat, 18 Jul 2026 19:40:00 +0800

TL;DR

Let’s fact-check the title first: TCP has not been abandoned — file downloads, video, email, and SSH still run on it today. But the Web really did change drivers: in June 2022, HTTP/3 became an official standard (RFC 9114), and it no longer uses TCP — web traffic is handed to QUIC, running over UDP.

TCP got “replaced” because of three incurable midlife conditions:

Head-of-line blocking: TCP is a byte stream that must be delivered in order — lose one parcel, and every parcel behind it stands at attention;

Expensive handshakes: before any data flows, 2-3 round trips of “small talk” (TCP handshake + TLS handshake) — half a second gone on intercontinental links;

A protocol welded shut: TCP lives inside the OS kernel, and middleboxes only recognize the “classic model” — improving it is nearly impossible.

QUIC’s fix is beautifully blunt: rebuild all of TCP’s wisdom on top of UDP, where nobody interferes. This is the finale of our networking trilogy — part one covered how to use the network, part two why TCP/IP was designed so well, and this one how even the mighty TCP got replaced by its own heirs. All screenshots come from real systems; IPs and hostnames are masked.

Connection Migration on Margrop Blog

TCP Ruled for 40 Years. Why Did HTTP/3 “Dump” It?