I'm having a hard time finding conclusive evidence on this: did MS put any kind of maximum concurrent TCP connection limit in Windows Server 2003 and/or 2008? (The equivalent of the XP SP2 "feature" they added...)

We're relooking at part of our architecture which is currently based on other technologies with using NetBIOS, but we'd need to be able to have 50-100 hosts connecting to 20-30 other hosts all over NetBIOS directly. Obviously a 10-connection limit (as it is in XP) will put a quick end to that particular plan.

  • Did you look for any evidence in the Event Viewer? – Gleb Nov 5 '09 at 14:28

AFAIK, the TCP concurrent connection limit in XP is not limited to 10 concurrent TCP connections, it's limited to 10 concurrent outgoing TCP connection attempts per second. This limit counts the number of NEW connections being established per second, not the number of ESTABLISHED connections. Will the hosts in question be making more than 10 outgoing TCP connections per second? You can quickly check to see if this is an issue by looking for Event ID 4226 in the Event log on one of the hosts.

  • Also, don't confuse this issue with client access limits. In XP there is a 10 client limit for clients accessing file and print services on an XP host. Windows Server has no such limit. – joeqwerty Nov 5 '09 at 13:04
  • Is half-open tcp connection really the same as concurrent tcp connection? – Sajuuk Jan 9 at 3:22

My understanding is that the limit does not exist in any of the server operating systems. However, if you are using this method than Microsoft licensing may dictate that you buy CALs for each of those connections (although there is no technical mechanism for preventing more connections than CALs).

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