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The Outlook Connection Error on Steelhead Appliances
Posted On Jan 12, 2009 at at 2:53 PM by Dophi This is a real case I have had in a Microsoft Exchange deployed network; Some clients experienced the connection errors due to the excess of maximum connections. By default, an Exchange server only allow 32 connections from a client (IP address). When the connections from a client are over the limitation, the client can’t connect to the Exchange server and a log is generated in Exchange server as below.
Event Type: ErrorThe reasons of this issue can be cataloged into two major types; with or without Riverbed Steelhead.
Event Source: MSExchangeIS
Event Category: General
Event ID: 9646
Description:
Closing Mapi session "/o=Organization/ou=Administrative Group/cn=Recipients/cn=Recipient" because it exceeded the maximum of 32 objects of type "session".
Without Steelhead:
,An Outlook client opens multiple connections (usually about 6 connections for Outlook 2003 and 10 connections for Outlook 2007) when it tries to communicate with an Exchange server and those connections remains for 1 hour. During the period, if a client loses its connection and tries to connect the same Exchange server (i.e the connection of an unstable wireless network or such), the connection count keeps increasing and consumes available connections. When the connections from the same client (IP address) reach 32, Exchange server refuses them.
With Steelhead:
The default connection keep-alive of LAN side of a Steelhead is 4 hours. When an Outlook losses connections in a branch, the connections remains for 4 hours in both headquarter and branch. If this client loses connection multiple times, these extra connections show up in Steelhead connection list and increase count. Finally, it causes the same issue as above.
Solutions: There are two solutions that we can make changes on either Exchange server or Steelhead.
On Exchange Server:
Refer to Microsoft Knowledge Base ID 842022 and change the maximum connections.
On Steelhead:
1. Disable MAPI Pre-population:
amnesiac (config) # no protocol mapi prepop enable
2. Verify the current connection settings: This is a hidden command. The default keep-alive time is 4 hours (2400 sec * 6 count) amnesiac (config) # show protocol connection internal
LAN:
Send socket buffer size: 81920 bytes
Receive socket buffer size: 32768 bytes
Keep-alive count: 6
Keep-alive interval: 2400 seconds
Keep-alive non-zero bytes: no
Half-closed keep-alive count: 6
Half-closed keep-alive interval: 20
Half-closed keep-alive non-zero: no
Delayed Acks disabled: no
WAN:
Default send socket buffer size: 262140 bytes
Default receive socket buffer size: 262140 bytes
Configured dynamic watermark: 5 milliseconds
Effective dynamic watermark (mxtcp):5 milliseconds
Inner keep-alive count: 6
Inner keep-alive interval: 300 seconds
Inner keep-alive non-zero size: no
OOB keep-alive count: 2
OOB keep-alive interval: 20 seconds
OOB keep-alive non-zero size: no
3. Decrease the LAN side keep-alive to 1 hour or less than it: It’s also a hidden command. In this example, I decrease the keep-alive to 1 hour (600 sec * 6 count)LAN:
Send socket buffer size: 81920 bytes
Receive socket buffer size: 32768 bytes
Keep-alive count: 6
Keep-alive interval: 2400 seconds
Keep-alive non-zero bytes: no
Half-closed keep-alive count: 6
Half-closed keep-alive interval: 20
Half-closed keep-alive non-zero: no
Delayed Acks disabled: no
WAN:
Default send socket buffer size: 262140 bytes
Default receive socket buffer size: 262140 bytes
Configured dynamic watermark: 5 milliseconds
Effective dynamic watermark (mxtcp):5 milliseconds
Inner keep-alive count: 6
Inner keep-alive interval: 300 seconds
Inner keep-alive non-zero size: no
OOB keep-alive count: 2
OOB keep-alive interval: 20 seconds
OOB keep-alive non-zero size: no
amnesiac (config) # protocol connection lan keep-alive interval 600
4. Restart Optimization service:amnesiac (config) # service restart
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