http://blogs.technet.com/b/mikelag/archive/2009/08/04/the-case-of-the-mysterious-exchange-server-hang.aspxRecently we had a case in which an Exchange 2003 server would hang and no longer accept any new RPC connections to the Information Store. The rest of the server seemed to be operating just fine, but it was the Store that was ultimately having the problemsen-USTelligent Evolution Platform Developer Build (Build: 5.6.50428.7875)http://blogs.technet.com/b/mikelag/archive/2009/08/04/the-case-of-the-mysterious-exchange-server-hang.aspx#3271255Thu, 06 Aug 2009 21:05:28 GMTd5e57398-b9ef-4490-9955-07cbb4e4a80d:3271255Mike Lagase MSFT<p>cnschindler - It appears to be network related, but setting MaxConcurrentAPI to 5 allows the server to continue operating when and if there are network problems going on. Instead of a 2 lane highway, we have a 5 lane highway now, so if 2 lanes of the highway are backed up, we still can process logon requests from the other lanes.</p> <p>slimwreck - If an authentication request comes in and is not for local auth, we will send the request through a secure channel to the DCs which is controlled via the MaxConcurrentAPI setting. </p> <div style="clear:both;"></div><img src="http://blogs.technet.com/aggbug.aspx?PostID=3271255" width="1" height="1">http://blogs.technet.com/b/mikelag/archive/2009/08/04/the-case-of-the-mysterious-exchange-server-hang.aspx#3271242Thu, 06 Aug 2009 20:46:42 GMTd5e57398-b9ef-4490-9955-07cbb4e4a80d:3271242slimwreck<p>i hear that maxconcurrentapi is reated to ntlm. why is ntlm being used and not kerberos???</p> <div style="clear:both;"></div><img src="http://blogs.technet.com/aggbug.aspx?PostID=3271242" width="1" height="1">http://blogs.technet.com/b/mikelag/archive/2009/08/04/the-case-of-the-mysterious-exchange-server-hang.aspx#3271053Thu, 06 Aug 2009 09:40:22 GMTd5e57398-b9ef-4490-9955-07cbb4e4a80d:3271053cnschindler<p>Very interesting post! Are you allowed to share what the root cause of the problem was(e.g. slow network ling, etc.)? Christian</p> <div style="clear:both;"></div><img src="http://blogs.technet.com/aggbug.aspx?PostID=3271053" width="1" height="1">http://blogs.technet.com/b/mikelag/archive/2009/08/04/the-case-of-the-mysterious-exchange-server-hang.aspx#3271007Thu, 06 Aug 2009 03:38:38 GMTd5e57398-b9ef-4490-9955-07cbb4e4a80d:3271007Jeff Stokes<p>Nice post Mike, way to go on this one.</p> <div style="clear:both;"></div><img src="http://blogs.technet.com/aggbug.aspx?PostID=3271007" width="1" height="1">