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We recently had a problem with maximum conncurrent connections on a Microsoft NLB cluster, that I got an answer to on stackoverflow:

http://stackoverflow.com/questions/909677/iis-6-0-server-too-busy-http-503-connectiondropped-defaultapppool

What I was wondering in addition was:

  • Is there a limit of 65,534 concurrent connections?
  • Is this limit per server, network card or NLB cluster?
    • Could we increase the number of concurrent connections by adding network cards to the servers?
  • Is this a limit in Microsoft technology or is it in the TCP/IP protocol?

Thanks

Shiraz

EDIT

Just to clarify: Even though all clients are calling the cluster IP address, the number of connections possible will be dependent upon the number of individual IP addresses in the cluster?

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3 Answers

up vote 1 down vote accepted
+100

You are running Server2003, but it still an interesting read even if it applies to Server 2008.

http://support.microsoft.com/kb/951764 http://msdn2.microsoft.com/en-us/library/cc150670(VS.85).aspx

...and since 2008 takes care of this issue and to answer your questions,

  • Yes

  • Per IP address (adding network interfaces would increase the number of IP addresses, so it seems reasonable that this would solve it).

  • This looks like a TCP/IP limitation especially since adding IP addresses "fixes" it.

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You do not need to add network cards to increase the number of ports. A single network card can have more than one associated IP address.

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65534, is the number of ports in use, if you want to configure IIS conncurrent connections follow this,

Increase the connection limit for the Web site. To do this, follow these steps: Click Start, point to All Programs, point to Administrative Tools, and then click Internet Information Services (IIS) Manager. Expand ComputerName, and then expand Web Sites. Right-click the Web site that you want to configure, and then click Properties. Click the Performance tab. Under Web site connections, click Connections limited to, and then type the connection limit that you want to set. Click OK, and then exit IIS Manager. Back to the top

Method 2

Set the connection limit for the Web site to an unlimited number of concurrent connections. To do this, follow these steps: Click Start, point to All Programs, point to Administrative Tools, and then click Internet Information Services (IIS) Manager. Expand ComputerName, and then expand Web Sites. Right-click the Web site that you want to configure, and then click Properties. Click the Performance tab. Under Web site connections, click Unlimited. Click OK, and then exit IIS Manager.

In answer to your other questions

Is there a limit of 65,534 concurrent connections? This is the port list... if you have an IIS server, say listening on port 80 mulitiple transfers from users would happen over this port. the concurrent connections can be configured as above.

Is this limit per server, network card or NLB cluster? limited by license, no max

Could we increase the number of concurrent connections by adding network cards to the servers? in theory no, but would increase the throughput

Is this a limit in Microsoft technology or is it in the TCP/IP protocol? dependent of end server througput, memory etc.. You may be able to get some stats from Microsoft on this.

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