The HTTP response consists of the status line, which is the first line of the response to the request and it contains a code along with a human readable phrase. The code is intended to be used by the user agent or the software agent for handling the response. On the other hand the phrase is simply a recommendation, so the human being reading the message can obtain further information about the response. The below post describes the HTTP status codes that are used by IIS 7.0, IIS 7.5, and IIS 8.0 .

1) 1xx - Informational

One of the most prominent status codes is the 1xx.These are considered informational status codes. They are provisional response, so there is a huge chance that they would be changed in the future. The client computer receives one or more 1xx responses which indicates to the user agent that it should carry on with the process of sending request, before the client computer receives a regular response.Once the request is complete, this code is totally ignored by user agent .

Eg. 100 means that the server has received the request headers, and that the client should proceed to send the request body (POST request)

2) 2xx - Success

Indicates that the server successfully accepted the request, implying that the request was received by server and successfully processed.

Eg. 200 means successful HTTP requests

3) 3xx - Redirection

This group of status code indicates that the client browser must take more action to access a particular resource. For example, the client browser may have to request a different page on the server. Generally user agent is automatically redirected to another resource without the interaction of the user.

Eg. 301 means a permanent redirect implying all future requests should be directed to the given URI.

4) 4xx - Client error

Indicates that there is a problem or an error occurred and that the client browser appears to be at fault. It tells the client that they should not send the same request again, but rather fix the error first. For example, the client browser may have requested a page that does not exist.

Eg. 400 means bad request

5) 5xx - Server error

These are all server error messages. They indicate even though the request appeared to be initially valid but was not completed because the server encountered an error.

Eg. 500 means internal server error