When analyzing your log files for data on your visitors, such as how they got to your site and where along with the search terms they used to find you, there’s even more information running around in there then you might think. In this guide, albeit a short and simple one, you will learn what types of server responses there are, the most popular and what to do with the information provided.

What is a Server Response?

If you are running your own website, you probably already know the basics of server responses, 200 good, 404 bad, but what you may not know are all the little ones in between. So let’s change that and learn what each server response does and what to do if you happen to see one in your logs.{mosgoogle}

First up, a quick primer on basic server responses:

1xx

These status codes were introduced for HTTP 1.1 and used at a low level during HTTP transactions.

2xx

200-series status codes indicate that the server understood the request and delivered the appropriate content.

3xx

300-series status codes generally indicate redirection. The request was valid, but the browser should find the content of its request elsewhere. These are mostly used when the naming scheme of a website changes to indicate where a page has gone.

4xx

400-series status codes indicate that there was an error with the request, either the page does not exist or the requesting party is not authorized to view the content of the request.

5xx

500-series status codes indicate there was an error on the server side and had nothing to do with the requesting party. This is usually indicative of a programming or configuration error.

Okay, now that you have the basic sets of server responses, let’s go into a little more detail and find out exactly what each server response means and what to do about it.

Basic 4xx Server Response

• 400 Bad Request: bad syntax used for the request. There is a low-level program bug in the client or the Web server or both, somebody entered a typo in the program code, either on the page or the browser that is requesting the page. The only thing you can do about this is check the page or file that was requested and see if you can replicate the response and try to figure out what went wrong.
• 401 Unauthorized: the request was made with insufficient credentials, either a login is required or the login information provided was incorrect. If you see multiple instances of 401 errors being generated by the same IP address or range of addresses, this could indicate that someone is trying to compromise your site. Or, they just might be bad at remembering passwords. Either way, keep a close eye on this type of error.
• 402 Payment Required: payment parameters for accessing the content of the request has not been met
• 403 Forbidden: the server denies the request regardless of the credentials supplied. This is another server response to watch as it could mean someone is attempting to compromise the server itself.
• 404 Not Found: the most common client error. The page requested can't be found on the server and there is no redirect in place to forward the request to the correct page.

Basic 5xx Server Response

• 500 Internal Error: the server encountered an unexpected condition that prevents if from fulfilling the request. This is usually a problem with the configuration of the server, most likely a file path problem.
• 501 Not Implemented: the server does not support the request made.
• 502 Service Temporarily Overloaded: the server can not process the request due to a high load. Keep an eye on these server responses making note of any reoccurring IP addresses and ranges as it could indicate a DOS (Denial Of Service) attack.
• 503 Gateway Timeout: similar to a 500 error, but where one server is making a request to another server, and the second server did not respond within the allotted timeframe given by the requesting server. Check to ensure that both servers are online and able to communicate.

Basic 3xx Server Response

• 301 Moved: represents a permanent change of the URI requested. These are especially useful when the naming structure of the site or the page has changed and you still want users to find the page their looking for.
• 302 Found: represents that the data requested actually resides at a different URL, and the browser is redirected automatically. Nifty eh?
• 303 Method: similar to the 302, except that a different method, other than GET, may be used to find the different URL.
• 304 Not Modified: Basically, if you request a page based on a set of conditions, and the page does not meet those conditions, then the page is not returned and a 304 response is received.