Properly configured Shadowsocks servers reportedly blocked in China


Authors: Anonymous

中文版: 据报配置正确的 Shadowsocks 服务器在中国遭封锁

Since March 2021, at least three users have reported that their Shadowsocks-libev servers became not pingable (temporarily in some cases) even after following the recommended setup in this tutorial (中文版). The tutorial documented how to setup a Shadowsocks-libev server that could defend against all known active probing attacks from the GFW as well as the partitioning oracle attack.

We document their reports in this post and we are taking immediate actions to investigate the causes.

At the same time, if you ever setup your servers by following our tutorial, we welcome you to report the status of your servers, no matter they are blocked or not. You can choose to:

  1. post under the original Net4People thread;
  2. post in the English comment section or Chinese comment section;
  3. or contact us privately (more contact information can be found at the footer of gfw.report).

Edited on May 5, 2021: add details from additional user report.

The first report says that on the night of March 3, 2021, the server was not responding temporarily and since the morning of March 4, the server had not been pingable from at least two different networks. The server remained not pingable for at least six hours until the user decided to discard the server. It appears that the user had setup the Shadowsocks server as recommended:

  • Used the latest version of Shadowsocks-libev at that time: shadowsocks-libev 3.3.5-1 751 latest/edge max-c-lv -;
  • Used an AEAD cipher: chacha20-ietf-poly1305;
  • Used a strong password generated by openssl rand -base64 18;
  • Used tcp_only mode;
  • Used ufw to only allow traffic to port 22 and the Shadowsocks port 24xxx;

The second report says that the server was not responding for half an hour on March 14, 2021, and has been working properly since then.

The third report says that the server was not pingable for approximately an hour on April 20, 2021, and has been working properly since then.

We were not able to find more reports on the recent blocking of Shadowsocks. Specifically, we looked up the open and closed GitHub issues in the following places:

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