Monitoring ESNI-related censorship across 14 geographic regions — including Mainland China, Iran, UAE, South Korea, and 10 others — found no blocking of ESNI traffic or interference with ESNIKey retrieval via DNS TXT records as of mid-2019, contradicting a widely circulated report claiming South Korea had already blocked ESNI. Additionally, the GFW's residual censorship window after a triggered RST was measured at 60 seconds (down from the previously reported 90 seconds).
From 2019-chai-importance — On the Importance of Encrypted-SNI (ESNI) to Censorship Circumvention
· §4.4, §6
· 2019
· Free and Open Communications on the Internet
Implications
The absence of ESNI blocking in 2019 (including in China and Iran) provided a narrow deployment window; circumvention infrastructure should be staged to maximize ESNI adoption before censors determine the false-positive cost of blocking it is acceptable.
The shortened GFW residual censorship window (60 s vs. 90 s) must be accounted for in connection retry and port-rotation logic to avoid triggering residual blocks during reconnection attempts.