Note: SSR Single Port Blocked, A Solution (Not Solved)

My “little airplane” proxy client stopped working. I tried V2Ray today. Same server, but V2Ray worked.
My guess is the port got blocked. I switched to another port, and it worked again.

While browsing Twitter, I found it’s not an isolated case. Others had the same issue.

刚才确认，今年第二次遇到这个情况：某台服务器，单个端口被封。https://t.co/WRsAGMVFVt

— David Frank (@bitinn) October 30, 2019

Someone in the comments provided a solution:
Feel the Bern – China Edition
使用 Fail2ban 封殺主動探測 IP

I haven’t tried it yet. Leaving it here.

Those tutorials are for RedHat. I found another Fail2ban tutorial: Use Fail2ban to Secure Your Server
My first test server failed. The second one seemed to work (but I still couldn’t fix the first one later; I’m too noob).

Tried again and realized I missed filter = ssr.
Also need to create /var/log/ssr.log and set logpath = /var/log/ssr.log.

Summary: add these lines to /etc/fail2ban/jail.local:

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[ssr]
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enabled = true
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filter = ssr
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logpath = /var/log/ssr.log
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port = 0:65535
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maxretry = 1
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bantime = 86400
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findtime = 300

Other parts are similar to the Fail2ban tutorial.

Common commands:

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fail2baj-client status
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fail2baj-client status ssr
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fail2baj-client reload

2019/11/21 update
The port got blocked again, switched to another port.
This fail2ban setup probably still isn’t right… (too little skill)

2019/11/27 update
ssr and v2ray are both unstable. Whether they work depends entirely on the “wall country’s mood”. Cultural confidence, cultural confidence.