执行1000多个HTTP请求任务失败

我正在尝试对API进行负载测试。我同时执行一个任务，每个任务执行一个HTTP请求。我Task.WhenAll(mytasks)用于等待所有任务完成。请求如下所示：

using (var response = await client.SendAsync(request).ConfigureAwait(false))
{
    using (var jsonResponse = await response.Content.ReadAsStreamAsync().ConfigureAwait(false))
    {
        var jsonSerializer = new DataContractJsonSerializer(typeof(Borders));
        var borders = (Borders)jsonSerializer.ReadObject(jsonResponse);
        return borders;
    }
}

至少可以处理多达数千个任务。但是，如果我开始更多，那么就会遇到几千个任务HttpRequestExceptions：

System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
   --- End of inner exception stack trace ---
   at System.Net.ConnectStream.WriteHeadersCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
   at System.Net.Http.HttpClientHandler.GetResponseCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at BusinessLogic.<GetBorder>d__6d.MoveNext() in c:\BusinessLogic.cs:line 757

所以我的问题是：为什么会发生这种情况（有1000多个任务）？我该如何预防？我显然可以将任务块切成小于1000的块，但我想将其留给底层系统...