[This is preliminary documentation and subject to change]

About Custom Error Messages

This topic contains conceptual information about default and custom HTTP 1.1 error messages.

HTTP 1.1 Error Messages
Custom Error Messages

HTTP 1.1 Error Messages

HTTP 1.1 error messages are returned to the client browser in the form of an HTML page that contains a generic message. When a user attempts to connect to a Web site and an HTTP error occurs, an error message is sent back to the client browser with a brief description of what happened during the attempt to establish a connection. For example, if a user attempts to connect to a Web site that has reached its maximum connection capacity, an HTTP error is returned to the client that contains the statement "Too many users."

Custom Error Messages

All IIS custom error messages display industry standard HTTP codes, which ensures consistency with HTTP 1.1 error messages. However, you can use the Custom Errors property sheet in IIS to customize generic HTTP error messages.

The following HTTP error messages can be customized with IIS:

Error Code	Error Message
400	Bad request
401.1	Logon failed
401.2	Logon failed due to server configuration
401.3	Unauthorized due to ACL on resource
401.4	Authorization failed by filter
401.5	Authorization failed by ISAPI/CGI application
403.1	Execute access forbidden
403.2	Read access forbidden
403.3	Write access forbidden
403.4	SSL required
403.5	SSL 128 required
403.6	IP address rejected
403.7	Client certificate required
403.8	Site access denied
403.9	Too many users
403.10	Invalid configuration
403.11	Password change
403.12	Mapper denied access
403.13	Client certificate revoked
403.14	Directory listing denied
403.15	Client Access Licenses exceeded
403.16	Client certificate un-trusted or invalid
403.17	Client certificate has expired or is not yet valid
404	Not found
404.1	Site not found
405	Method not allowed
406	Not acceptable
407	Proxy authentication required
412	Precondition Failed
414	Request-URI too long
500	Internal server error
500.12	Application restarting
500.13	Server too busy
500.15	Requests for Global.asa not allowed
500-100.asp	ASP error
501	Not implemented
502	Bad gateway

Notes

Custom error messages appear as a list in the IIS snap-in which is treated as a single property by IIS. For example, when a set of custom error messages is configured at the Web site level, all directories under that server inherit the entire list of custom error messages. That is, the two custom error message lists (for server and directory) are not merged.
A custom error for HTTP Error 503.1 will be sent to clients if a Web server has exceeded its CPU process throttling limits. This error will inform the client that the Web server has either been paused or stopped due to exceeding these set limits. For more information, see Throttling Processes.
The 404.1 error can occur only on computers with multiple IP addresses. If a a specific IP address/port combination receives a client request, and the IP address is not configured to listen on that particular port, IIS returns a 404.1 HTTP error. For example, if a computer has two IP addresses and only one of those IP addresses is configured to listen on port 80, then any requests received on the other IP address with port 80 will result in IIS returning a 404.1 error. This error should be set only at the service level because it will be returned to clients only when multiple IP addresses are used on the server.