Addendum 2: HTTP Status Codes

This section contains reference information for the HTTP protocol that you can use to troubleshoot HTTP messages with Message Analyzer.

HTTP Status Codes

The table that follows describes common HTTP client and server StatusCodes and associated ReasonPhrases that can be returned from HTTP message exchanges between client browsers and web servers. Definitions for these codes and phrases are widely known to most networking audiences; however, they are reproduced here for user convenience, to provide the benefit of having this information readily available when performing various procedures in this documentation.

Table A1. HTTP StatusCode and ReasonPhrase Definitions

StatusCode ReasonPhrase Definition
Common Client Errors
400 Bad Request Indicates a syntax error in the request, which is therefore denied. This is basically an error message from the web server indicating that the web browser incorrectly attempted to access a resource or the request was corrupted.
401 Authorization Required Indicates that the request header did not contain the necessary authentication codes and therefore the requesting client is denied access. This error usually occurs when a website visitor attempts to access a restricted webpage but does not have authorization to do so, often because of a login failure.
403 Forbidden Can indicate that a client is not permitted to view a particular file or has attempted to access a forbidden directory. This StatusCode is also returned when the web server is unable to accommodate more visitors. Note that this error is similar to the 401 authentication error, although in the case of the 403 error, there was no login opportunity available.
404 Not Found Indicates that a requested resource was not found on the server, typically because it does not exist. This error can also be caused by the invalid spelling of a URL, a broken link, or the resource was moved to another location.
405 Method Not Allowed Indicates that the method being used by a requestor to access a resource is not permitted.
406 Not Acceptable Indicates that the requested resource exists but cannot be returned to the client system because of an incompatible format.
407 Proxy Authentication Required Indicates that the request must be authorized before proceeding any further.
408 Request Timed Out Often the result of heavy network traffic, which could indicate that a web server is overburdened.
409 Conflicting Request Might be that there are too many concurrent requests for a resource, which can be indicative of the inability of a server to handle the amount of requests it is receiving.
410 Gone Indicates that a resource previously existed in a particular location, but is no longer present there.
411 Content Length Required Indicates that the request is missing the required Content-Length header.
412 Precondition Failed Indicates that the client does not have the required configuration set up for a resource to be delivered by the web server.
413 Request Entity Too Long Indicates that the requested resource is too large to process.
414 Request URI Too Long Indicates that the entered URI address is too long for the server.
415 Unsupported Media Type Indicates that the file type specified in the request is unsupported.
Common Server Errors
500 Internal Server Error Could indicate an overloaded web server that cannot properly handle the requests it is receiving.
501 Not Implemented Indicates that the request cannot be performed by the web server.
502 Bad Gateway This error usually indicates one or more of the following:

- Improperly configured proxy servers.

- Faulty IP communication between back-end computer nodes.

- The client’s ISP is overloaded.

- A firewall is improperly functioning.

Typically can be resolved by clearing the client cache to force a different proxy server into use to resolve the web server content.
503 Service Unavailable Indicates that the requested service, file, or resource is currently unavailable.
504 Gateway Timeout Indicates that the server gateway has timed out, which could indicate that one or more servers are over-burdened by heavy network traffic. Time-outs can occur when a server in a chain of servers does not receive a timely response from another server, indicating slow communication between upstream computers.
505 HTTP Version Not Supported Indicates that the server does not support the HTTP version in use for the client request.