问IIS服务器上的IDPmetadata url出现问题- ITfoxtec -未知此类主机

EN

System.Net.WebException: No such host is known. No such host is known.
System.Net.Http.HttpRequestException: No such host is known.
System.Net.Sockets.SocketException (11001): No such host is known.
at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken 
cancellationToken)
End of inner exception stack trace ---

at System.Net.HttpWebRequest.GetResponse()
at System.Net.WebClient.GetWebResponse(WebRequest request)
at System.Net.WebClient.DownloadBits(WebRequest request, Stream writeStream)
at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request)
at System.Net.WebClient.DownloadString(Uri address)
at ITfoxtec.Identity.Saml2.Schemas.Metadata.EntityDescriptor.ReadIdPSsoDescriptorFromUrl(Uri 
idPMetadataUrl)