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High Latency over VPN

avineshp asked
Medium Priority
Last Modified: 2012-06-21

Please could someone help with this,
We have a 10MB internet link at a client in South Africa, from there we have a VPN tunnel up to the Denamrk HQ. We haev really high latency at around 240ms pings. We have just added riverbed stealhead on both sides on the network using it in Out-of-Path mode, however we are not see any difference, on email or any applications.

Is it better to have the emails configured in Exchange Cached Mode or not?

Please could someone assist with a way to increase performance.

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Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Cached Mode allows for having the emails offline. I don't think it makes a difference in regard of speed while having a connected Exchange.

The latency is related to VPN? Did you compare non-VPN and VPN latency yet?
There will be less utilization of bandwidth with Outlook in cached mode.  However, you may want to control Offline Address Book downloads as they can grow to large sizes in large environments.

As for Riverbed, I would suggest disabling any Exchange/MAPI optimization - if it improves your WAN performance, you will need the vendor to correctly configure it for you.  

1.  Are you mentioning Avg RPC Latency?  Or is that just ping?
2.  What version of Exchange and Outlook?


Thanks for the comments,

@Qlemo: Unfortunately we have to connect to Denmark via VPN as we have to connect to the corporate network at HQ.

@infin: 1: Im refering to both RPC latency and the normal pings.
2: Using Exchange and Outlook 2010

When you click on a new email it takes about 30sec or more to just open and during this time Outlook just hangs, with the annoying message the Oulook is trying to retrieve data from the exchange server.

Is there any other means you can recommend that we can try?

Thanks in advance
I've seen quite a few cases of Riverbed accelerators being the root cause of Exchange performance issues over WANs.  If there is low utilization of the WAN link, there's a good chance that this is the case.  It would be important to know what the traffic is like during peak hours.  Also determine if the performance is the same during off peak hours (outside of any backup/maintenance schedules).

I'm not sure what the pings should be from South Africa to Denmark but you should check if you're getting the same without VPN (ping the public CAS interface for OWA and compare to any other Danish web servers)

More things to try
1.  Do a network trace to check for dropped packets over the WAN link or on the LAN.  Packet drops are not good for RPC and even more so for RPC/HTTPS.  
2.  Use PAL (pal.codeplex.com) to investigate performance of the CAS and Mailbox servers in Denmark, after getting a good 1 or 2 days worth of performance data
3.  Disable realtime AV scanning on clients
4.  Check performance of your VPN servers - find out if they are at capacity.  VPN appliances are not all made equal.
5.  Try running Outlook in safe mode (outlook /safe)
6.  Ctrl - Right click on the Outlook icon in the system tray > Connection Status > take note of the results there in particular Req/Fail and Avg Resp.  High fails indicate packet loss somewhere in the network
7.  Turn on advanced RPC logging for Outlook http://support.microsoft.com/kb/2260527, reproduce issue and attach the resulting etl file