title: NetTcpActivator service (Net.Tcp Listener Adapter) stops responding occasionally
body: <p>In my current project we (I mean "project team") use WCF services hosted on IIS.</p>
  
  <p>Here are some technical details which may be important:</p>
  
  <ol>
  <li>We use NET 3.5 for WCF services</li>
  <li>We use NET.TCP communication protocol</li>
  <li>We use both IIS 7 and IIS 7.5 to host these services</li>
  <li>We use multiple IIS worker processes on each server</li>
  </ol>
  
  <p>So, the problem is - sometimes WCF-services become unavailable. When we try to reach these WCF-services we get timeout error. And the only way to restore WCF-service functioning is to restart NetTcpActivator (Net.Tcp Listener Adapter) Windows service.</p>
  
  <p>According to my colleague's theory, this error may be related to the problems described in this KB article:</p>
  
  <blockquote>
    <p>FIX: Smsvchost.exe for the WCF service stops responding when you run a .NET Framework 4-based WCF service <a href="http://support.microsoft.com/kb/2536618" rel="noreferrer">http://support.microsoft.com/kb/2536618</a></p>
  </blockquote>
  
  <p>According to this article, SMSvcHost (container service which hosts NetTcpActivator and Port Sharing Service) hangs up if it can't route a request to w3wp (IIS worker process) in over 60 seconds (non-configurable timeout). Unfortunately, we are unable to find the way to reproduce this error. For example, we limited SMSvcHost to 1 CPU core and 1 thread and extended pending connections limit to 1M and pushing it to 100% CPU load in user mode. And it didn't hang!</p>
  
  <p>Sometimes our load tests lead to strange errors, but when we stop them, all services automatically recover to their normal state. But sometimes not a heavy load may hang NetTcpActivator!</p>
  
  <p>In addition, I would like to say that this is not a new problem. My colleagues already got it 3 years ago (see this thread for additional information <a href="http://forums.iis.net/t/1167668.aspx/1/10" rel="noreferrer">http://forums.iis.net/t/1167668.aspx/1/10</a>). And, unfortunately, they didn't get the answer. The problem just disappeared after some configuration changes! And now it came back on the new server.</p>
  
  <p>I will really appreciate all you thoughts and ideas!</p>