我在阿里的服务器上ping CDN的IPping不通。

[dmartin1]

I am not seeing a 521 error on this domain, it appears as a 200.

You should checks this servers settings if you are on unable to ping on this.

More for information on fixing error 521:

Troubleshooting Cloudflare 5XX errors | Cloudflare Support docs

Community Tip - Fixing Error 521: Web server is down

Error Try the suggestions in this Community Tip to help you fix Error 521: Web server is down. Background A 521 error happens when we are unable to make a TCP connection to your origin server. Specifically, Cloudflare tried to connect to your origin server on port 80 or 443, but received a connection refused error. This is often caused by security or firewall software and happens if the origin server has directly refused Cloudflare’s proxy request. [Banner in tip catalog] Quick Fix Ideas …