Which Cumulative Updates are these Exchange 2013 servers at?

I would concur with Li's recommendation to upgrade the .NET to 4.5.2. While that fixes issues with Garbage Collection and performance issues and alleviate some of your issues, I still think you may have a different underlying cause for requests queuing up.

Also check the TcpKeepAlive and TCP Time Outs on devices between the clients and Exchange CAS server. The default value on Windows is 2 hours. It is always recommended that Exchange is the one with the least value (typically 15 mins) and then devices in front of Exchange going all way to the Client is higher than the value set on Exchange. This way Exchange (Server) is the one responsible for closing or leaving the session open.

Also to answer your question if Recycling the App Pool will be advisable: You can certainly do that which will provide temporary relief but if you don't address the root cause, the issue might still return after a while.  

• Edited by Sainath Vijayaraghavan Tuesday, August 11, 2015 4:49 AM

We are at CU7 and have .NET 4.5.2 installed, but probably do not have the latest patches. Off to verify.

I have two CAS only role servers providing access to 6 MB servers supporting roughly 18,000 mailboxes.

Occasionally I have issues with users losing their connection to their mailbox. In researching this I found that on the CAS servers I see the MSExchangeRpcProxyFrontEndAppPool IIS worker using over 8GB memory. Looking for any Perfmon counters that may relate, I found the MSExchange HttpProxy / Outstanding Proxy Requests for instance rpchttp has over 20,000 outstanding requests.

Both the 8GB usage and the 20,000 outstanding requests sound very high to me. Is this out of line?
Would recycling the IIS App Pool for MSExchangeRpcProxyFrontEndAppPool be advisable?

Any other ideas?

Thanks!
Tom

My suggestion would be,

• Upgrade .Net Framework to 4.5.2 with the latest hotfix rollup
• Patch the OS with the latest critical and security patches
• Upgrade Exchange with the latest CU if your current one is CU5 or earlier

Which Cumulative Updates are these Exchange 2013 servers at?

I would concur with Li's recommendation to upgrade the .NET to 4.5.2. While that fixes issues with Garbage Collection and performance issues and alleviate some of your issues, I still think you may have a different underlying cause for requests queuing up.

Also check the TcpKeepAlive and TCP Time Outs on devices between the clients and Exchange CAS server. The default value on Windows is 2 hours. It is always recommended that Exchange is the one with the least value (typically 15 mins) and then devices in front of Exchange going all way to the Client is higher than the value set on Exchange. This way Exchange (Server) is the one responsible for closing or leaving the session open.

Also to answer your question if Recycling the App Pool will be advisable: You can certainly do that which will provide temporary relief but if you don't address the root cause, the issue might still return after a while.  

• Edited by Sainath Vijayaraghavan 2 hours 37 minutes ago

Hi,

Cumulative Update 9 for Microsoft Exchange Server 2013 was released on June 16, 2015, please upgrade to latest version for testing.

If this issue persists, we can change the recycling setting for MSExchangeRpcProxyFrontEndAppPool:
1. Open IIS manager and switch to Application Pool.
2. Select MSExchangeRpcProxyFrontEndAppPool and click Advanced Settings.
3. Scroll down to Recycling to set the value for memory and request.

Hope it will help.