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I am having trouble downloading the Service Index file. I have searched probably the whole internet for a solution, but none of the found ways solved the problem. Well, I have a Nuget repository problem at work:

Unable to load the service index for source https://api.nuget.org/v3/index.json. An error occured while sending the request. The underlying connection was closed: An unexpected error occured on a send".

I can download the file in any browser except Internet Explorer (the error description suggests a problem with invalid TLS/SSL). I found a script to test downloading the file for every encryption protocol supported by the system, but none worked. The problem is occurring on Windows 10, Visual Studio 2019, and Visual Studio 2022 and appeared after a system update last Thursday/Friday.

I have tried:

  • adding a proxy entry to devenv.config in the <system.net> section
  • changed TLS-related settings in the registry (disabling TLS13, enabling TLS12), entries forcing TLS usage on NET
  • deleting in the user directory a file with a list of nuget repositories
  • reinstall visual studio

From a coworker I received a (probably old address) nuget repository (https://nuget.org/api/v2) that works without problems. Anyone have any idea how else to bite the problem with v3?

JohnVanClouds
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1 Answers1

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According to the description, you cannot open it in IE browser. You can try the following steps:

  1. Check if you have proxy variable heep_proxy in your system variables or in the IE browser.
  2. If you have the proxy setting in your PC, you can remove it or add proxy settings into Nuget.config file.
  3. You can refer these links for more info: Nuget Config Section and Nuget Proxy Settings
  4. After confirming that we don't have any proxies in our PC, we should check if our network is limited. We can test it with different networks.

You can also refer to the similar issue:

Nuget connection attempt failed "Unable to load the service index for source"

Visual Studio - Nuget - Unable to load the service index for source

Jingmiao Xu-MSFT
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  • It's only limited to IE and it works last week before last windows update. Others browser open file without problems and only IE show error about problems with tls/ssl configuration. And I do not have any proxy. I tried turn off and on automatic proxy detection in windows settings without change anything. – JohnVanClouds May 21 '22 at 08:53
  • What is the version of IE after your update. [This link](https://learn.microsoft.com/en-us/troubleshoot/developer/browsers/security-privacy/cannot-display-https-site) shows that SSL 2.0 and TLS 1.2 are incompatible with each other in Internet Explorer 9 and later may prevent HTTPS sites from being displayed. – Jingmiao Xu-MSFT May 23 '22 at 05:25