Understanding Web Error Messages

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More correctly known as HTTP Status Codes (HTTP version 1.1 status codes)


400 Series Codes

The 400 series of Status Codes are known as "Client Errors" and are given the number range of 400-499. Currently there are 17 in this category:

400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Request Entity Too Large
414 Request-URI Too Long
415 Unsupported Media Type
416 Requested Range Not Suitable
417 Expectation Failed

500 Series Codes

The 500 series of Status Codes are known as "Server Errors" - their number range is 500-599. The 500 series contains 6 Status Codes.

500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
505 HTTP Version Not Supported

Some of these errors will never be seen by the average web surfer (hopefully) so we will be going over a few of the more frequently seen by web users.

Client Errors

Let's take a look at the "Client Errors" first as they are the most commonly encountered.

400 - BAD REQUEST

Sometimes followed by the text "The syntax of the request was not understood by the server."

There's something wrong with the address you entered. There may be a space where there shouldn't be or even a mispelled extension; i.e. "page.cig " instead of "page.cgi" - or "page.htlm" instead of "page.html". Sometimes you may have the "slashes" going the wrong direction - slashes in web addresses will always be "forward" in direction. Check that all the names are properly spelled. Web addresses can be case sensitive, especially when directories are included in the url.

Bottom line: You probably mis-typed or mis-spelled something.

401 - UNAUTHORISED

Sometimes followed by the text "The request needs user authentication"

You can't access the website because you're not on the guest list, your password is invalid or you have entered your password incorrectly.

Bottom Line: The site and/or directory you are trying to access is password protected. You must have the correct information (username/password) to access it.

403 - FORBIDDEN

Essentially the same as a 401. The site or directory is not allowing access without the proper authorisation.

404 - NOT FOUND

This probably the most commonly seen of all of the Status Codes... the dreaded "Page Not Found" error. Either the web page no longer exists on the server or it can not be found by the server.Check the address carefully and try entering it again. You might also see if the site has a search engine. If so, use it to hunt for the document. (It's not uncommon for pages to change their addresses when a website is redesigned.) To get to the home page of the site, delete everything after the domain name and hit the Enter or Return key.

Server Errors

Now we will look at some of the 500 series of "Server Errors".

501 - Not Implemented

Sometimes followed by the text "The request was unsuccessful because the server can not support the functionality needed to fulfill the request." Or similar mumbo jumbo.... This one is complicated and hard to understand by the lay web surfer but here goes:

Your Web server does not understand or does not support the HTTP method it finds in the HTTP data stream sent to it by the client.

Any client (e.g. your Web browser) goes through the following cycle when it communicates with your Web server:

  • Obtain an IP address from the IP name of your site (your site URL without the leading 'http://'). This lookup (conversion of IP name to IP address) is provided by domain name servers (DNSs).
  • Open an IP socket connection to that IP address.
  • Write an HTTP data stream through that socket.
  • Receive an HTTP data stream back from your Web server in response. This data stream contains status codes whose values are determined by the HTTP protocol. Parse this data stream for status codes and other useful information.

This error occurs in the final step above when the client receives an HTTP status code that it recognises as '501'.

Source: www.checkupdown.com

Bottom Line: There is nothing you can do about these errors when you encounter them. The server's support department needs to be contacted and informed when this occurs. Always have as much detail, concerning your actions when you received the error,

503 - SERVICE UNAVAILABLE

Sometimes followed by the text "The request was unsuccessful to the server being down or overloaded." Your Internet service provider (ISP) or your Internet connection may be down. IT could also mean that your host is down, performing maintainance or repairs. Bottom Line: The request for that URL is not going through. Usually just wait a while and try again. If it continues beyond a tolerable period of time you should contact your host or ISP for additional information.


Other Errors

There are some other other messages you may encounter other than the standard HTTP Status Codes. I have listed a few below.

BAD FILE REQUEST

Problem: Your browser supports forms complete with data-entry fields and drop-down lists, but not the form you're trying to access. Perhaps there's an error or unsupported feature in the form and your web browser may not be able to decipher the this feature's structure. There may also be a technical error in the form. Bottom Line: There is not a great deal you can do about this other than trying a different browser. You might consider sending a message to the site's webmaster, providing any technical information you can, such as the browser and version you use.

CONNECTION REFUSED BY HOST

The server is probably too busy to handle one more user, but it's not configured to generate its own message, so this generic message shows up instead. Bottom Line: This another one of those "Try again later" issues. At some point, usually fairly soon, the browser will "catch up" and you will be able to connect.

FAILED DNS LOOKUP

DNS stands for the Domain Name System, which is the system that looks up the name of a website, finds a corresponding number (similar to a phone number), then directs your request to the appropriate web server on the Internet. When the lookup fails, the host server can't be located. This is either a harmless glitch or the result of a mistyped URL (specifically, a mistyped host name) Bottom Line: Glitches in DNS lookup are common, and often you can rectify this by clicking the Reload button. If that doesn't work, check your typing of the URL carefully. If the problem persists, try again after an hour or so.

FILE CONTAINS NO DATA

The site you've accessed is the right one, but there are no Web page documents on it. You may have stumbled upon this site just as updated versions are being uploaded. Bottom Line: Check the address and enter it again. If you get the same error message, try again later.

HOST UNAVAILABLE

The machine that hosts this site is probably down for maintenance, repairs or upgrades. Bottom Line: Yet another "Try again later" situation... give it a little time and reload the page or enter the address again.

HOST UNKNOWN or UNABLE TO LOCATE HOST

The server may be down for maintenance, or you may have lost the connection (your modem/cable or DSL has become disconnected). Bottom Line: Yet another "Try again later" situation... give it a little time and reload the page or enter the address again.

NETWORK CONNECTION REFUSED BY SERVER

Explanation: Similar to the "Connection Refused..." error above. The server is probably too busy to handle one more user, but it's not configured to generate its own message, so this generic message shows up instead. Bottom Line: Try again in a while. :)

UNABLE TO LOCATE SERVER

The web server is out-of-business, offline or you have entered the url incorrectly. Bottom Line: Check the address and try typing it again. Do a search on a search engine for the source name. It's possible that the party you are looking for may have changed their domain name or address.

FINAL NOTE

We hope this helps you to better understand the nature and reasoning behind these web errors.

If you find a descrepancy within the above "How To" or would like to make an addition please u2u me with the details and I will make the necessary corrections or addtions after a review of the information.

Thanks
Daf