在主机上的Dockerfile或ubuntu shell中运行dotnet restore命令时，显示以下错误：
Restoring packages for /src/Customer/Customer.API/Customer.API.csproj...
Restoring packages for /src/Customer/Customer.DTO/Customer.DTOs.csproj...
/usr/share/dotnet/sdk/2.1.302/NuGet.targets(114,5): error : Unable to load the service index for source https://api.nuget.org/v3/index.json. [/src/Customer/Customer.API/Customer.API.csproj]
/usr/share/dotnet/sdk/2.1.302/NuGet.targets(114,5): error : The SSL connection could not be established, see inner exception. [/src/Customer/Customer.API/Customer.API.csproj]
/usr/share/dotnet/sdk/2.1.302/NuGet.targets(114,5): error : Authentication failed because the remote party has closed the transport stream. [/src/Customer/Customer.API/Customer.API.csproj]
我还设置了http_proxy和https_proxy环境变量（企业代理），并且成功下载了docker映像，只有此命令失败。
编辑： 现在的错误是这样的：
/usr/share/dotnet/sdk/2.1.302/NuGet.targets(114,5): error : Unable to load the service index for source https://api.nuget.org/v3/index.json. [/home/dev/Repos/MVPChina/Customer/Customer.API/Customer.API.csproj]
/usr/share/dotnet/sdk/2.1.302/NuGet.targets(114,5): error : An error occurred while sending the request. [/home/dev/Repos/MVPChina/Customer/Customer.API/Customer.API.csproj]
/usr/share/dotnet/sdk/2.1.302/NuGet.targets(114,5): error : SSL connect error [/home/dev/Repos/MVPChina/Customer/Customer.API/Customer.API.csproj]
此外，我无法从此ubuntu服务器ping 8.8.8.8或www.google.com
curl命令也会失败：
$ curl https://api.nuget.org/v3/index.json
curl: (35) gnutls_handshake() failed: The TLS connection was non-properly terminated.