Windows Server 2003 Is there a limit on number of TCP connections per process?

Question

We are running into issues with BizTalk host instance intermittently going down. One of the things that we are worried about is the number of FTP connections a single host instance is making which could easily reach into the hundreds perhaps sometimes thousands, depending on traffic.

My question is Windows Server 2003 Is there a limit on number of TCP connections per process? If so would putting each application in it's own host instance potentially solve the problem.

Solution

There's a lot of other things that are likely to be exhausted before you run out of TCP connections. An FTP server should not crap out for a few thousand connections.

Read this article and the rest of the series. Plus, just do your normal troubleshooting. Anything in the windows System or Application event logs? Is there an application log that you could review? Do the IIS logs tell you anything (assuming IIS is your FTP server)?

There's a lot of things you need to check on before you start guessing that you've run out of TCP connections.

OK - here's a pretty good link for you to start looking into then. That's a lot of new info for me, and I'm still a little surprised that Mark R hasn't delved into it. Of course, it has little to do with kernal data structures except for the TCB, so maybe he doesn't much care :-)

Comments

[mfinni]

You know, this is something that isn't addressed in Mark R's "pushing the limits" series. blogs.technet.com/b/markrussinovich/archive/2009/09/29/…

[Daniel Dessinger]

The FTP server BizTalk is connecting to is a iSeries Mainframe Unix box that our group has no control over. Also the weird thing is that there is absolutely no errors or warning in the system or application event log, which is what has us scratching our heads. We have also run biztalk health check which has yielded no red flags, though we have not run it long enough for the instance to shut down.

[TomTom]

Stupid question, but do THEY have a connection limit in place? ;)

[mfinni]

I'm not sure I'm understanding you. The BizTalk instance is running on your Windows server, and the mainframe is making FTP connections to your Windows machine? That means that your windows machine is running an FTP server. Unless I've misunderstood you - if the Windows machine is making FTP connections to the mainframe?

[Daniel Dessinger]

The windows server is making connections to (outbound) the mainframe, it is polling directories hosted on the mainframe. Also we have confirmed that they have configured their FTP server for an very large number of concurrent ftp connections, though I am unsure if the max number of TCP connections on that box is an issue. I assume that a windows box would run into problems with an issue like that before a mainframe would.

[Daniel Dessinger]

@mfinni I suspect you are correct, however it would be nice to know if windows did set a limit and what that limit was in order to rule it out, since it was mentioned as a possibility. I think next step is going to be SCOM. I appreciate the help!

[mfinni]

OK - updated my answer for you to look a little further. It's not just TCP connections, it could be TCP-related but in the TCB, paged pool, who knows.