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Exchange Team Blog
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Client Connectivity in an Exchange 2013 Coexistence Environment

Ross Smith IV's avatar
Ross Smith IV
Icon for Microsoft rankMicrosoft
Mar 12, 2014
This article is part 3 in a series that discusses namespace planning, load balancing principles, client connectivity, and certificate planning. Over the last several months, we have routinely fie...
Updated Jul 01, 2019
Version 2.0
Client Access
Exchange 2013
on premises
outlook
OWA
Planning and Architecture
Deleted's avatar
Deleted
Mar 28, 2014
I have two questions about how CAS2013 proxies connections to legacy CAS servers (2010 in our case).

1. The article explains that the 2013 CAS server pings the target legacy CAS server to determine if it is available. However, it is not clear what method is being used to select a target. Does it use logic similar to the Exchange Shell where it starts with the first CAS in the legacy CAS array and works its way down, or does it use some sort of load balancing algorithm?

2. How does session affinity come into play with proxied connections to legacy servers? I know CAS2013 is stateless, but CAS2010 is not. If we use a stateless load balancer configuration without session affinity, we know CAS2013 will work just fine with Exchange 2013 mailboxes. However, we are unsure of how CAS2013 handles the non-stateless CAS2010. Will using a stateless load balancer configuration cause problems with Exchange 2010 in a co-existence configuration?