Get WebException on compatible S3 storage - vb.net

Question

I develop an application that connects with a compatible S3 server located in an internal network. For that reason, the server where this app is going to run does not have internet connectivity.
I am using the amazon web service sdk (AWSSDK.S3) to connect with the server and it provides all the necessary functionality.
When I try to connect with the server, it seems that the SDK tries to connect with a real amazon webservice server and it fails.
This is the code I am trying
Dim config As AmazonS3Config = New AmazonS3Config With {
.ForcePathStyle = True,
.ServiceURL = cloudEndpoint,
.RegionEndpoint = Amazon.RegionEndpoint.GetBySystemName(region)
}
config.Validate()
s3Client = New AmazonS3Client(cloudAccessKey, cloudSecretKey, config)
Dim listBuckets As ListBucketsResponse = s3Client.ListBuckets()
The S3Client is generated correctly but when I tried to get the buckets, I get the following exception:
Error creating s3. Exception: Amazon.Runtime.AmazonServiceException: A WebException with status ConnectFailure was thrown. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond ** 52.216.143.230:80 **
at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception)
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.GetResponse()
at Amazon.Runtime.Internal.HttpRequest.GetResponse()
at Amazon.Runtime.Internal.HttpHandler`1.InvokeSync(IExecutionContext executionContext)
at Amazon.Runtime.Internal.RedirectHandler.InvokeSync(IExecutionContext executionContext)
at Amazon.Runtime.Internal.Unmarshaller.InvokeSync(IExecutionContext executionContext)
at Amazon.S3.Internal.AmazonS3ResponseHandler.InvokeSync(IExecutionContext executionContext)
at Amazon.Runtime.Internal.ErrorHandler.InvokeSync(IExecutionContext executionContext)
--- End of inner exception stack trace ---
at TestS3.S3CDM..ctor(String endpoint, String accessKey, String secretKey, String region, String bucketName)
at TestS3.Form1.btn_CreateConnector_Click(Object sender, EventArgs e)
The server (52.216.143.230:80) that appears in the exception is not my s3 server, searching I find that it´s an amazon server.
Is it necessary connectivity to internet to use this SDK? Or I forget any additional configuration?
Thank you in advance.