ActiveSync - CAS

I'm not quite sure how ActiveSync works when working with two load balanced CAS servers.
Do they use the same CAS server for a certain lenght of time ? Or do they costantly talk to either server ?

I was doing a test like refreshing my inbox on the mobile device and I can actually see IIS traffic on both CAS servers. So how does it actually work ? I cannot find any material to explain this. Would love to get an insight.

Thanks so much.
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AkhaterSolutions ArchitectCommented:
Depends on your load balancing technology
AkhaterSolutions ArchitectCommented:
If you have a dedicated load balancer it is usually configured to use cookie insert for sticky sessions so one client will connect to one cas server until the cookie expires or the server goes down

If you are using Windows load balancing it is typically random / round robin

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ferraristaAuthor Commented:
We are actually using round robin.
What puzzles me is that I find transactions on both servers at basically the same time, so that got me thinking....

I'm actually trying to resolve a problem where EAS performance has suddenly decreased.
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AkhaterSolutions ArchitectCommented:
No a connection will happen only to one of the servers at a time
Simon Butler (Sembee)ConsultantCommented:
Round Robin isn't load balancing.
If you are seeing problems, then take it out. Ensure all traffic goes to one server.
If you want HA for CAS, then you need a load balancer. Kemp or JetNexus are the most common ones I deploy.
ferraristaAuthor Commented:
Hi, we use NLB,,,very simple load balancer. But I doubt that is the problem.
AkhaterSolutions ArchitectCommented:
I'm sorry Simon but Round Robin is load balancing

All load balancers have a RR mode and even DNS round Robin provides Load Balancing. Maybe not HA in the case of 2010 but definitely load balancing in its most basic form
Simon Butler (Sembee)ConsultantCommented:
No, round robin is not load balancing.
Round robin has no concept of the load.
DNS round robin has no concept of service availability. If a server goes down then DNS keeps sending traffic to that place.

Windows NLB is not recommended by the Exchange product team for use with Exchange. Get a proper load balancer.

Even so, if any kind of load balancer is involved it has to be bypassed to confirm it is not the cause of the problems. Never presume it is not the cause, because in my experience they usually are, or you cannot do anything until you have shown they are not.
AkhaterSolutions ArchitectCommented:
I am aware of all that but since users will be randomly distributed around the servers it is safe to assume that the load will be balanced even though it is a random distribution and not a smart one

The fact that it is not service aware makes it not suitable for high availability (which I said in my previous post)
AkhaterSolutions ArchitectCommented:
Btw I'm not arguing with idea to bypass it or that it might be the source of the issue just debating the sentence that round robin is not load balancing
ferraristaAuthor Commented:
OK....since we use an alias that points to the virtual node of the nlb cluster, is it acceptable to simply change the alias to point to one of the two physical nodes rather than the virtual one ? This way the change is very straight-through.
AkhaterSolutions ArchitectCommented:
Yes off course this is the way to do it
AkhaterSolutions ArchitectCommented:
Should have enough info to answer the request
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