What causes Error 400?

Question

When I connect to a 4G network, I keep getting an intermittent Error 400.

My ISP claims one of the following:

• A machine problem (I tell them it happens on all machines)
• A router issue (I tell them it happens when I connect directly to the dongle I'm using)
• Geographical coverage! It happens in many places, but not as recurring as it is in my current location

Questions:

• How true is that?
• Can location cause this specific Error 400?
• What can I do to fix that locally if at all possible?
• What can I tell my ISP technical care to help them figure it out (When they tried the dongle on their machine, it did not fire any errors!)

Note: I get that error on all browsers, and I got it on all systems (Windows 8, Windows 10, Android's Chrome), but I cannot confirm yet if I get any of that on Skype, WhatsApp, or other services that use the internet).

Also note: I have other providers, when I switch to those other providers, I get no issues.

I use no proxy servers.

Extra:

Here is an example of what I get on fiddler: 326 The Server did not return properly formatted HTTP Headers. HTTP headers should be terminated with CRLFCRLF. These were terminated with LFLF.

Extra:

One website was generous to give me the following error message upon a 400 error, does it mean anything?

Solution

When I connect to 4g network I keep getting an intermittent Error 400

There are a number of different causes for a "400 Bad Request Error"

See below for some troubleshooting steps you can follow to try and resolve the issue.

Notes:

• Most of these are clients side issues.
• The ones that aren't are issues with the web server
• They are unlikely to be caused by your ISP (but anything is possible).

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How To Fix a 400 Bad Request Error

The 400 Bad Request error is an HTTP status code that means that the request you sent to the website server, often something simple like a request to load a webpage, was somehow incorrect or corrupted and so the server couldn't understand it.

400 Bad Request errors appear differently on different websites so you may see something from the short list below instead of just "400" or another simple variant like that:

How You Might See the 400 Error

• "400 Bad Request"
• "Bad Request. Your browser sent a request that this server could not understand."
• "Bad Request - Invalid URL"
• "HTTP Error 400 - Bad Request"
• "Bad Request: Error 400"
• "HTTP Error 400. The request hostname is invalid."
• "400 - Bad request. The request could not be understood by the server due to malformed syntax. The client should not repeat the request without modifications."

The 400 Bad Request error displays inside the Internet browser window, just as web pages do. 400 Bad Request errors, like all errors of this type, could be seen in any operating system and in any browser.

In Internet Explorer, a "The webpage cannot be found message" indicates a 400 Bad Request error. The IE title bar will say "HTTP 400 Bad Request" or something very similar to that.

Windows Update can also report HTTP 400 errors but they display as error code 0x80244016 or with the following message:

WU_E_PT_HTTP_STATUS_BAD_REQUEST.

A 400 error that's reported for a link within a Microsoft Office application will often appear as "The remote server returned an error: (400) Bad Request." message within a small pop-up window.

Cause of 400 Bad Request Errors

The 400 Bad Request error is oftentimes caused by entering or pasting the wrong URL in the address window but there are some other relatively common causes as well.

Note: Web servers running Microsoft IIS often give more specific information about the cause of a 400 Bad Request error by suffixing a number after the 400 as in HTTP Error 400.1 - Bad Request, which means Invalid Destination Header. You can see a complete list here.

How To Fix the 400 Bad Request Error

1. Check for errors in the URL.

   The most common reason for a 400 Bad Request error is because the URL was typed wrong or the link that was clicked on points to a URL with a specific kind of mistake in it, like a syntax problem.

   Important: This is most likely the problem if you get a 400 Bad Request error. Specifically, check for extra, typically non-allowed, characters in the URL like a percentage character. While there are perfectly valid uses for something like a % character, you won't often find one in a standard URL.

2. Clear your browser's cookies, especially if you're getting a Bad Request error with a Google service.

   Many sites report a 400 error when a cookie it's reading is corrupt or too old.

3. Clear your DNS cache, which should fix the 400 Bad Request error if it's being caused by outdated DNS records that your computer is storing.

   Do this in Windows by executing ipconfig /flushdns from a Command Prompt window.

   Important: This is not the same as clearing your browser's cache (next thing to try below).

4. Clear your browser's cache.

   A cached, but corrupt copy of the web page you're trying to access, but are getting the 400 error on, could be the root of the problem.

   Clearing your cache is unlikely the fix for the majority of 400 bad Request issues, but it's quick and easy, and so worth trying.

5. While this is not a common fix, try troubleshooting the problem as a 504 Gateway Timeout issue instead, even though the problem is being reported as a 400 Bad Request.

   In some relatively rare situations, two servers may take too long to communicate (a gateway timeout issue) but will incorrectly, or at least unhelpfully, report the problem to you as a 400 Bad Request.

6. Contact the website directly that hosts the page.

   It's possible that the 400 Bad Request error actually isn't anything wrong on your end and it's something they need to fix, in which case letting them know about it would be very helpful.

   Tip: If an entire site is down with a 400 Bad Request error, searching Twitter for #websitedown, as in #facebookdown or #gmaildown is often helpful. It certainly won't contribute anything to fixing the issue, but at least you'll know you're not alone!

Source How To Fix a 400 Bad Request Error

Comments

[ReinstateMonica3167040]

Accept his answer if it was helpful to you.

[Ayyash]

Sorry but there is no answer, I simply dumped my ISP for a new one, I no longer get the 400, it is definitely an ISP issue

[Ayyash]

I tried most of that, the problem occurs when i'm on this specific ISP, I have other providers, I do not get 400s when I am connected to any of them, so it cannot be the website's problem, it is either ISP, or a combination of ISP-device.

[NotAdmin Dave]

@Ayyash I know you mentioned that you aren't running a proxy. But can you confirm that your ISP isnt running a transparent proxy of some sort? I do know some ISP's run them so they can provide NetNanny type services to their end users.

[Ayyash]

So you are saying, one of the questions i should ask them if they are running a proxy? Or is it something i can confirm myself?

[NotAdmin Dave]

You will not be able to determine if they are running one if it's transparent. But they perhaps may be running one to save on costs by caching content, you should call them and verify.

[Ayyash]

I went through almost all the steps provided, none of it seems to have an effect, it is caused by the provider because it never occurs on other connections. I just don't know how to report the problem to them lazy customer service!

[Ayyash]

I changed my ISP eventually, I no longer see the problem, so it was the ISP for sure

[ReinstateMonica3167040]

Doesn’t the picture show there’s a proxy? Proxy IP: ###.##.###.38