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Load Balancing CAS Array and OA Question - Exchange 2010

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  • Load Balancing CAS Array and OA Question - Exchange 2010

    I am getting ready to deploy a failover exchange 2010 server. Currently the setup we have is using 2 NICs. A private and public IP are assigned to the 2 NIC's. We have our CAS array setup using the private IP and outlook anywhere uses the public IP.

    I've read through and setup test environments load balancing the cas array with no issues but this is only using the private IP with a smart host smtp relay. For the public IP would I configure it the same way as the CAS array?

    My thinking is this, I will need 3 public IP's and 3 private IP's. 3 private for the CAS array load balancing and 3 publics for the OA load balancing. Does OA ultimately use the CAS array? Can I set both CAS and OA up the same in NLB and if one server dies, OA will failover to the same server that the CAS Array has now failed over to?

  • #2
    Re: Load Balancing CAS Array and OA Question - Exchange 2010

    A CAS array is an Exchange object that is used by the Outlook Clients to connect. It's just that the DNS record you create for the CAS array name points to the VIP address assigned to the load balancer. For example, Windows NLB. Generally, you would ensure that you rename all Exchange URLs to be the same External DNS name and ensure that internally those external DNS names point to the internal VIP address of the CA servers via split DNS configuration with only the autodiscover internal URI starting with autodiscover.External.Domain as oppose to something like mail.External.Domain.

    Your services, such as OWA, OA etc. would then share the same internal VIP address and one External IP. Each web service ends with /uniquename, so for example, https://mail.External.Domain/owa and a different one for other services; https://mail.External.Domain/etc.

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    • #3
      Re: Load Balancing CAS Array and OA Question - Exchange 2010

      OK. I'm still slightly confused.

      Let me explain this in my words and tell me if this is what you were saying.

      So I setup my NLB for the cas array as usual. 1 VIP talking to the private ips of each server. I change all the URL's in exchange to my cas array URL. I keep those DNS entries for all the replaced URL's and change the IP's to match the VIP. I create an entry for the cas array dns name on the public nameserver and point it to the public IP giving me split DNS. That way someone from outside the organization will get directed to the public.

      Do I still need 3 public IP's and setup a 2nd NLB cluster using those? It would seem that I do as if the NIC with the public IP assigned to it were to die, then DNS would not resolve.

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      • #4
        Re: Load Balancing CAS Array and OA Question - Exchange 2010

        And as a follow up, my next question would be, is that not going to force internal clients to use OA instead of MAPI? Is there any issues doing that? I know thats how 2013 works anyway. Almost seems like it would be best to just keep them separate dns names and load balance them without using split dns.

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        • #5
          Re: Load Balancing CAS Array and OA Question - Exchange 2010

          The CAS Array is used internally only. It should not be used for anything else, such as Outlook Anywhere etc.

          You can use the same IP address, just use another host name.
          Doing that will not force the clients to use Outlook Anywhere.

          Although if you want reliable failover and performance, don't use WNLB, use a proper load balancer.

          Simon.
          --
          Simon Butler
          Exchange MVP

          Blog: http://blog.sembee.co.uk/
          More Exchange Content: http://exchange.sembee.info/
          Exchange Resources List: http://exbpa.com/
          In the UK? Hire me: http://www.sembee.co.uk/

          Sembee is a registered trademark, used here with permission.

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          • #6
            Re: Load Balancing CAS Array and OA Question - Exchange 2010

            Thank you for your help guys.

            OK so I keep a different host for OA. That's fine and I have no issues there. But as far as load balancing OA vs CAS Array, would I just set them up the same?

            Virtual Public IP with a public assigned to each server NIC talking to each other with NLB for OA and Virtual private IP with a private assigned to each servers 2nd NIC using NLB for CAS Array?

            My issue is that if load balancing the cas array is setup and OA uses a different hostname with a public IP assigned to that host, if a server fails users outside the organization wont get the failover benefit. If I can load balance OA the same way I load balance CAS Array then I'm good.

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            • #7
              Re: Load Balancing CAS Array and OA Question - Exchange 2010

              A load balancer is just load balancing the IP address, not the host name.
              Therefore if you have a host name for Outlook Anywhere just point that at the virtual IP address of the load balancer. If you are using an internal IP address, then NAT the external IP address to the internal virtual IP address.

              Simon.
              --
              Simon Butler
              Exchange MVP

              Blog: http://blog.sembee.co.uk/
              More Exchange Content: http://exchange.sembee.info/
              Exchange Resources List: http://exbpa.com/
              In the UK? Hire me: http://www.sembee.co.uk/

              Sembee is a registered trademark, used here with permission.

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