Addendum 2: HTTP Status Codes


Updated: October 26, 2016

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

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

Common Client Errors
400Bad RequestIndicates 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.
401Authorization RequiredIndicates 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.
403ForbiddenCan 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.
404Not FoundIndicates 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.
405Method Not AllowedIndicates that the method being used by a requestor to access a resource is not permitted.
406Not AcceptableIndicates that the requested resource exists but cannot be returned to the client system because of an incompatible format.
407Proxy Authentication RequiredIndicates that the request must be authorized before proceeding any further.
408Request Timed OutOften the result of heavy network traffic, which could indicate that a web server is overburdened.
409Conflicting RequestMight 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.
410GoneIndicates that a resource previously existed in a particular location, but is no longer present there.
411Content Length RequiredIndicates that the request is missing the required Content-Length header.
412Precondition FailedIndicates that the client does not have the required configuration set up for a resource to be delivered by the web server.
413Request Entity Too LongIndicates that the requested resource is too large to process.
414Request URI Too LongIndicates that the entered URI address is too long for the server.
415Unsupported Media TypeIndicates that the file type specified in the request is unsupported.
Common Server Errors
500Internal Server ErrorCould indicate an overloaded web server that cannot properly handle the requests it is receiving.
501Not ImplementedIndicates that the request cannot be performed by the web server.
502Bad GatewayThis 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.
503Service UnavailableIndicates that the requested service, file, or resource is currently unavailable.
504Gateway TimeoutIndicates 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.
505HTTP Version Not SupportedIndicates that the server does not support the HTTP version in use for the client request.

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