原因可能有以下几点：
- 1、源站宕机、间歇性卡慢。 请检查源站的存活状态。如何检查源站状态（超链接到某个帮助）。
- 2、源站缓慢响应超时30秒。 超过30秒未响应的请求会被安域断开，显示502。
- 3、请核查在安域DNS设置配置的源站IP是否正确，是否还留存错误的、已经不使用的服务器IP。
- 4、请检查源站防火墙是否拦截安域节点IP
- -如果空间服务商的防火墙拦截安域节点IP， 请与空间商联系解封并加白IP段。
- -如果服务器防火墙（安全狗等）拦截安域节点IP，请将安域的IP段添加到服务器防火墙白名单中。
- -如果您服务器未配置任何防火墙，请与您的机房联系，将安域的IP段添加到机房防火墙白名单中
Using Focus Shield protection, why there will be 502, snapshots?
The reason may have the following:
- 1.The source station downtime, intermittent card is slow.Please check the source station the survival of the state.How to check the source station status(hyperlink to a certain help)
- 2.The source station slow response timeout for 30 seconds.More than 30 seconds did not respond to requests will be Focus Shield disconnect, according to 502.
- 3.Please check stood Focus Shield DNS Settings configuration of the source IP is correct, whether also retained the wrong, has not use server IP.
- 4.Please check whether the source station firewall intercept Focus Shield node IP see the FAQ for details
- -if IP firewall intercept Focus Shield node space service provider, please contact the quotient space unlock and add white IP.
- -if the server IP firewall (security dogs, etc.) interceptor Focus Shield node, please add Focus Shield IP segment to the server firewall in the white list.
- -if you have not any firewall configuration server, please contact with your room, firewalls add Focus Shield IP segment to the room in the white list
