What is limiting the # of simultaneous connections my ASP.NET application can make to a web service?

Most of the answers provided here address the number of incoming requests to your backend webservice, not the number of outgoing requests you can make from your ASP.net application to your backend service.

It's not your backend webservice that is throttling your request rate here, it is the number of open connections your calling application is willing to establish to the same endpoint (same URL).

You can remove this limitation by adding the following configuration section to your machine.config file:

<configuration>  <system.net>    <connectionManagement>      <add address="*" maxconnection="65535"/>    </connectionManagement>  </system.net></configuration>

You could of course pick a more reasonable number if you'd like such as 50 or 100 concurrent connections. But the above will open it right up to max. You can also specify a specific address for the open limit rule above rather than the '*' which indicates all addresses.

MSDN Documentation for System.Net.connectionManagement

Another Great Resource for understanding ConnectManagement in .NET

Hope this solves your problem!

EDIT: Oops, I do see you have the connection management mentioned in your code above. I will leave my above info as it is relevant for future enquirers with the same problem. However, please note there are currently 4 different machine.config files on most up to date servers!

There is .NET Framework v2 running under both 32-bit and 64-bit as well as .NET Framework v4 also running under both 32-bit and 64-bit. Depending on your chosen settings for your application pool you could be using any one of these 4 different machine.config files! Please check all 4 machine.config files typically located here:

• C:\Windows\Microsoft.NET\Framework\v2.0.50727\CONFIG
• C:\Windows\Microsoft.NET\Framework64\v2.0.50727\CONFIG
• C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config
• C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config

I realize the question might be rather old, but you say the backend is running on the same server. That means on a different port, probably other than the default port 80.

I've read that when you use the "connectionManagement" configuration element, you need to specify the port number if it differs from the default 80.

LINK: maxConnection setting may not work even autoConfig = false in ASP.NET

Secondly, if you choose to use the default configuration (address="*") extended with your own backend specific value, you might consider putting the specific value first! Otherwise, if a request is made, the * matches first and the default of 2 connections is taken. Just like when you use the section in web.config.

LINK: <remove> Element for connectionManagement (Network Settings)

Hope it helps someone.

Might it be possible that you're using a WCF-based web service reference? By default, the ServiceThrottlingBehavior.MaxConcurrentCalls is 16.

You could try updating your service reference behavior's <serviceThrottling> element

<serviceThrottling    maxConcurrentCalls="999"     maxConcurrentSessions="999"     maxConcurrentInstances="999" />

(Note that I'd recommend the settings above.) See MSDN for more information how to configure an appropriate <behavior> element.