C# Web - localhost:port works, 127.0.0.1:port doesn't work

Question

I just finished adding C# Web API components (Web API Models & Controllers) to a localhost copy of an existing project.

This Web API's GET-methods should be called from an Android app. In this link it's explained I should use 10.0.2.2 on the Android Emulator to get the computer's 127.0.0.1.

When I did this, it didn't work for my HttpRequest in the Android app. So I went to the Android browser and typed it directly, and it also didn't work.

Then I tried using 127.0.0.1 instead of localhost in my computer's browser, and for some unknown reason it also doesn't work.. Is there a different between localhost and 127.0.0.1? I always thought they were one and the same.

Here is the 400 error I get when using 127.0.0.1:

And with localhost everything works fine.

So, my question: How can I use localhost on the Emulator (or, how can I fix the error I get when using 127.0.0.1 instead of localhost)? Also, I would like to know the difference between localhost and 127.0.0.1, since I always thought they were the same.

Thanks in advance for the responses.

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Edit 1:

In this stackoverflow question they mention the host file in System32 of Windows. I opened this file with Notepad++ (as Administrator) and uncommented the lines with 127.0.0.1 localhost and ::1 localhost. But unfortunally this didn't fixed the problem and I still can't use 127.0.0.1 on my computer as a replacement for localhost. Probably because my problem is the reversed (I can access localhost, but not 127.0.0.1, instead of the other way around.)

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Edit 2:

In this stackoverflow answer it's explained that the differences between localhost and 127.0.0.1 are:

• 127.0.0.1 will be more easily recognized as an IP in some programming languages.
• localhost can be changed to another IP in the computer's host-file (the file mentioned in my Edit 1).
• There are some differences between IPv4 and IPv6.

All and all I kinda understand the differences now, I just don't get why my localhost is working, but 127.0.0.1 isn't..

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Edit 3:

Does it have to do something with the port (I use 54408 as port)? I've opened cmd and did the following tests:

• ping localhost: I'm getting a response with 4 times Reply from ::1: time<1ms.
• ping 127.0.0.1: I'm getting a response with 4 times Reply from 127.0.0.1: bytes=32 time<1ms TIL=128
• ping localhost:54408: I'm getting an error Ping request could not find localhost:54408. Please check the name and try again.
• ping 127.0.0.1:54408: I'm getting an error Ping request could not find 127.0.0.1:54408. Please check the name and try again.

And like I've said before: 127.0.0.1:54408 in the browser gives the error seen in the image above. And localhost:54408 works just fine..

Still no one with an idea on how to fix this?

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Edit 4:

Copy of my hosts-file, located in C:\Windows\System32\drivers\etc.

# Copyright (c) 1993-2009 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
#      102.54.94.97     rhino.acme.com          # source server
#       38.25.63.10     x.acme.com              # x client host

# localhost name resolution is handled within DNS itself.
127.0.0.1   localhost
::1         localhost

The last two lines used to be:

#      127.0.0.1     localhost
#      ::1           localhost

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Edit 5 / Semi-Solution:

After Jake C's suggestion I went looking for Visual Studio port configuration and found the following site. At the section "To specify a port for a Web application project that uses the Visual Studio Development Server" I followed the instructions and changed the Web option in the Project Properties to Use Visual Studio Development Server with my 54408 port.

This was a great step in the right direction, since 127.0.0.1:54408 homepage now works. However, once I try to log in with the Google OAuth on the C# website, I was getting the following error:

One of my ex-colleagues who worked on the C# web project told me once about this stackoverflow post. In the answer of this post is stated that I should add the redirect-urls (in my case 127.0.0.1) to the Google APIs Console. Right now I don't have access to this Console for my localhost project however, since it's obtained through SVN. I will ask to one of my supervisors for permission to view the Google APIs Console of this C# web project and perhaps edit the redirect-urls to include 127.0.0.1.

Once I've got it completely working I'll accept Jake C's answer, since his explanation of the Http port configurations did indeed help me find the answer.

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Edit 6:

Ok, I've used my own Google APIs Console and created a new Project with a new Client ID. I've added both the http://localhost:54408/Account/ExternalLoginCallback and http:127.0.0.1:54408/Account/ExternalLoginCallback to the redirect-urls. Then in my C# web project's App_Start/AuthConfig.cs I've changed the Client settings to use this new client.

Once again thanks Jake C for your suggestion to change the http port configurations in Visual Studio. This did the trick for me.

Answer 1

If you are using Visual Studio's built in web server (IIS Express), localhost is mapped by default; to enable 127.0.0.1:

1) At path: %USERPROFILE%\Documents\IISExpress\config

2) Locate config file: applicationhost.config

3) - open config file in editor (I use notepad++)

4) Search for the site port, for example if the url is typically localhost:57578, search "57578" and you should find:

<binding protocol="http" bindingInformation="*:57578:localhost" />

5) Change this entry to:

<binding protocol="http" bindingInformation="*:57578:*" />

6) Save and exit, restart website.

Note: You will want to repeat this process any time you create a new virtual directory (changing the port number Project/Properties/Web/Project Url), which creates a new entry in the applicationhost.config file.