Using load balancing router causes problems with Exchange Server

Posted on 2011-04-18
Last Modified: 2012-05-11
We just set up a load balancing router (Cisco RV042) which joins two 4 Mbps DSL lines coming into our office. We can actually get 8 Mbps downloads at a computer if the rest are fairly idle (which was unexpected; I expected it would allow simultaneous 4 Mbps downloads but not this. Client is thrilled). Anyway, the constant switching of IPs at each computer is causing a lot of issues with our third party Exchange server. By the time it has authenticated in Outlook or OWA, the IP of the computer changes and boom, it needs to reconnect. It actually often completely prevents successful login to OWA and causes Outlook crashes.

What is the best way to fix this? I see an option to limit bandwidth to certain IPs. I think I could tell it to only send traffic to the servers (I have all the IPs) through one of the DSL lines, but that seems like it would make all the computers have the same IP all the time or not be able to connect at all.
I also could assign computers to pools for the lines, but that defeats the purpose. How do I allow each computer to maximize speed while still being able to get email?
I have initiated dialog with the support team of the Exchange host, but if you give a better or faster solution; you get points!

Currently, I just disabled one of the lines, so we're back to one until this is fixed.
Question by:TommySzalapski
    LVL 26

    Expert Comment

    My experience with dual WAN over the RV042 is that it breaks LOTS of things.  For example, try logging in to your account at ....  Your Exchange problems are just scratching the surface.

    It's not the RV042's fault; there are lots of sites out there that expect to see every packet in a particular transaction coming from the same IP address, and object if they don't.

    I think before you spend a lot of time trying to solve the Exchange problem, you should see how many other problems you'll also have to solve if you retain the dual-WAN setup.

    Depending on how your loads are, you might want to try sending all HTTP traffic through one of the two lines, and compensate by sending everything else through the other... if you look at your logs, you might find that your traffic could be divided approximately 50/50, most of the time, by allocating some services to one WAN port and other services to the other.
    LVL 44

    Accepted Solution

    Any HTTPS traffic will experience this problem.  Each HTTPS session will be logged by source IP, and if your traffic comes from another source IP (the other line) you will be asked to re-authenticate again.

    You can try fixing HTTPS to one line only using a route-map.
    LVL 37

    Assisted Solution

    Ah, that makes sense. HTTPS should fix most of the places that have issues (I had already seen that logmein was an issue, ironically, but the client doesn't use it so I was working on the email first). That's also a relatively light load. I guess the router doesn't understand the idea of a session and can't be taught.
    LVL 37

    Author Closing Comment

    I added my last comment as part of the solution because I wasted about an hour on the bandwidth management tab before I figured it out. Hope this can save someone else from the same fate.

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