IIS status code reflects the request processing result, 2xx indicates success, such as 200 (OK), 201 (Created), 204 (No Content); 3xx indicates redirection, such as 301 (Moved Permanently), 302 (Moved Temporarily), 304 (Not Modified), 307 (Temporary Redirect); 4xx indicates client error, such as 400 (Bad Request), 401 (Unauthorized), 403 (Forbidden), 404 (Not Found), 405 (Method Not Allowed), 410 (Gone); 5xx indicates server error, such as 500 (Internal Server Error), 501 (Not Implemented), 502 (Bad Gateway), 503 (Service Unavailable), 504 (Gateway Timeout); you can view it through the sc-status field in the IIS log, or you can use the log analysis tool to further troubleshoot problems.

IIS (Internet Information Services) uses various status codes to indicate the server's response to client requests. These status codes are part of the HTTP standard, and IIS returns them when processing requests to help developers and administrators understand whether the request is successful, whether further operations are required, or what problems arise.

Here are some common sc-status (HTTP status) codes and their meanings, suitable for IIS logs and responses:

2xx series: Request successful

These status codes indicate that the client's request has been successfully received, understood and processed by the server.

• 200 OK
  The most common success status code indicates that the request has been successfully completed. For example, when accessing an existing web page, it usually returns 200.

• 201 Created
  Indicates that the request was successful and a new resource was created, usually used after a POST request.

  

• 204 No Content
  The request is successful, but no content is returned in the response, and is often used in API requests.

3xx series: redirection

This type of status code means that the client needs to take further actions to complete the request.

• 301 Moved Permanently
  Indicates that the requested resource has been permanently moved to the new location and the browser or client should update the bookmark.

• 302 Found (Moved Temporarily)
  The resource is temporarily moved to another URI, but will be changed back in the future.

• 304 Not Modified
  Used for caching mechanism, indicating that the content cached by the client is still valid and does not need to be re-downloaded.

• 307 Temporary Redirect
  Similar to 302, but it requires that the original HTTP method (such as POST) be maintained when redirecting the request.

4xx series: Client error

This type of status code indicates that the client may have sent an incorrect request.

• 400 Bad Request
  Indicates that the server cannot understand the client's request, usually due to a malformed request.

• 401 Unauthorized
  Requests require user authentication, which is commonly found in protected resources.

• 403 Forbidden
  The server understands the request, but refuses to execute. For example, access directories or files without permissions.

• 404 Not Found
  The requested resource does not exist. This is one of the most common and easiest to identify errors.

• 405 Method Not Allowed
  Request methods (such as POST, GET) are not allowed, for example, sending POST requests to pages that only GET is allowed.

• 410 Gone
  The requested resource has been permanently deleted and the server knows this.

5xx series: Internal server error

These status codes indicate that an error occurred during the server processing the request.

• 500 Internal Server Error
  The most common server error indicates that IIS encountered an unexpected situation while processing the request.

• 501 Not Implemented
  The server does not support requested features, such as certain HTTP methods.

• 502 Bad Gateway
  This error occurs when IIS acts as a reverse proxy if the backend server returns an invalid response.

• 503 Service Unavailable
  Indicates that the server is temporarily unable to process the request, usually due to overload or maintenance.

• 504 Gateway Timeout
  Returns when the proxy server waits for the backend server to respond to a timeout.

How to view status codes in IIS?

If you are viewing an IIS log file (such as W3C log format), the status code usually appears in the sc-status field. For example:

 #Fields: date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) sc-status ...
2025-04-05 10:12:34 192.168.1.10 GET /index.html - 80 - 192.168.1.20 Mozilla/5.0 200

You can also analyze these status codes by customizing the error page or using log analysis tools such as LogParser, ELK, Splunk.

Basically that's it. Different status codes reflect different problems. During troubleshooting, you can combine sc-substatus and sc-win32-status to further locate.

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