Why Windows 11 Update 24H2 Causes TCP Timeout Errors
Windows 11 Update 24H2 introduced a change to the TCP/IP stack’s default initial congestion window (IW, initial window). The update increased the default IW from 10 to 30, which allows Windows to send more data in the initial TCP burst. While this improves performance for most connections, it can cause timeout errors on CDN edge nodes that implement rate limiting based on the initial burst size — the CDN may interpret the larger initial burst as a DDoS attack and drop the connection before the TCP handshake completes.
Update 24H2 also changed the default setting for TCP Auto Tuning Level from Normal to Experimental, which can cause unstable TCP behavior on certain network adapter configurations, resulting in premature connection timeouts.
Resolving Post-Update 24H2 TCP Timeouts
Resetting TCP Auto Tuning to Normal Level
Open Command Prompt as Administrator and run:
netsh int tcp set global autotuninglevel=normal
Restart the PC. This resets the TCP auto tuning to the pre-24H2 default, eliminating the experimental behavior that may be causing connection timeouts.
Disabling TCP Fast Open
Open Command Prompt as Administrator and run:
netsh int tcp set global fastopenlevel=disabled
Restart the PC. TCP Fast Open (TFO) uses cookie-based authentication to accelerate the TCP handshake, but 24H2’s TFO implementation can conflict with certain CDN configurations, causing the handshake to timeout before TFO cookies are validated.
Rolling Back Windows 11 Update 24H2
If the above fixes do not resolve the timeout errors, rollback the update: open Settings → Windows Update → Update history → Uninstall updates. Find KB5044380 (the 24H2 cumulative update) and uninstall it. Restart the PC and test Chrome. Note that rolling back updates is a temporary measure — Microsoft will eventually re-offer the update, and the above fixes should be applied before re-installing.
Call to Action
Use the webs.ninja gateway to test TCP handshake latency after applying the TCP auto tuning and Fast Open reset. If timeouts persist after the resets, the issue may be the 24H2 update itself — in this case, use the rollback procedure above and monitor for a Microsoft fix in a subsequent update.