1.什么是Http 403错误
Http协议中对403错误定义如下
The server understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it SHOULD describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client, the status code 404 (Not Found) can be used instead.
服务端接收用户请求，但是拒绝响应。服务器可以返回拒绝响应的原因，如果不希望返回客户端具体原因，可以使用404（Not Found）来代替。

2.IIS中对Http 403错误的详细分类
403.1 – Execute access forbidden.
服务器禁止执行

403.2 – Read access forbidden.
服务器禁止读

403.3 – Write access forbidden.
服务器禁止写

403.4 – SSL required.
必须使用SSL协议访问服务器

403.5 – SSL 128 required.
必须使用SSL 128协议访问服务器

403.6 – IP address rejected.
IP地址黑名单

403.7 – Client certificate required.
需要客户端证书

403.8 – Site access denied.
拒绝访问服务器

403.9 – Forbidden: Too many clients are trying to connect to the Web server.
连接数太多

403.10 – Forbidden: Web server is configured to deny Execute access.
服务器禁止执行

403.11 – Forbidden: Password has been changed.
服务器访问密码已修改

403.12 – Mapper denied access.

403.13 – Client certificate revoked.
客户端证书不存在

403.14 – Directory listing denied.
不允许访问目录

403.15 – Forbidden: Client access licenses have exceeded limits on the Web server.

403.16 – Client certificate is untrusted or invalid.
客户端证书不被信息

403.17 – Client certificate has expired or is not yet valid.
客户端证书失效

403.18 – Cannot execute requested URL in the current application pool.
不能执行请求地址

403.19 – Cannot execute CGI applications for the client in this application pool.
不能执行相应的CGI应用接口

403.20 – Forbidden: Passport logon failed.
服务器访问密码不对

403.21 – Forbidden: Source access denied.

403.22 – Forbidden: Infinite depth is denied.

403.502 – Forbidden: Too many requests from the same client IP; Dynamic IP Restriction limit reached.
IP访问限制