檢視防火牆狀态，檢視socket監聽，端口鍊路測試
systemctl status firewalld #檢視防火牆狀态
netstat -nltp #檢視socket監聽
端口鍊路測試 #能 ping 通但端口不通時端口可用性探測說明
https://help.aliyun.com/knowledge_detail/40572.html?spm=5176.11065259.1996646101.searchclickresult.570737b5EznKbR能 ping 通但端口不通時端口可用性探測說明
https://help.aliyun.com/knowledge_detail/40572.html?spm=5176.11065259.1996646101.searchclickresult.2c825b9d2RlWIG![高防伺服器、高防IP與高防CDN的差別[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)