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Proxy traffic when internet down

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  • Proxy traffic when internet down

    I'm designing an Exchange 2010 setup for an organization with two sites. Both sites have their own internet connections and are connected via a separate dedicated WAN connection. Each site will have a server hosting all 3 roles and will be a member of two DAGs. There will be two MB databases, each as a member of a separate DAG. The reason for this is to allow normal operation to continue if the WAN link goes down.

    My question is: how can I proxy traffic through the WAN link if the internet connection at one site goes down? From what I've read in this document: I would need to not configure an external URL for one of the sites, however, I want each site to be accessed via it's own internet connection during normal operation.

    Is there a way to have the server in the site that's up proxy traffic through the WAN link to the server that hosts the active database for the connecting mailbox user only when the internet is down for that user's site? Right now I'm thinking perhaps a script that executes every minute or so to determine if the internet is up in that site and if not, runs a PowerShell command to change the external URL of the problematic site to null.

    Any input is appreciated.
    Last edited by agreenbhm; 25th May 2011, 11:22.
    Drew Green
    MCITP:EA & Messaging 2010, MCSE:S, CCENT

  • #2
    Re: Proxy traffic when internet down

    What do you mean by "traffic"? OWA? MAPI?

    Where is the user sitting in this scenario when the link goes down?
    Twitter: @ExchServPro


    • #3
      Re: Proxy traffic when internet down

      The main type of traffic is going to be ActiveSync and Outlook Anywhere, but OWA will probably be used as well. My understanding is that if a user connects to the CAS in site A and their mailbox is in site B they will be redirected to the correct CAS in site B. This is how I want my setup to function normally, but if the internet is down in site B and they are unable to be redirected, I want CAS traffic to proxy from the CAS in site A to the CAS in site B via the WAN link. Please let me know if you need more details. Thanks for the help!
      Drew Green
      MCITP:EA & Messaging 2010, MCSE:S, CCENT


      • #4
        Re: Proxy traffic when Internet down

        There is a flaw in your design to begin with.
        If you want two DAGS, then you will need four servers.
        A server cannot be a member of two different DAG implementations. DAG is a per server setting.

        Therefore you would need two servers in each location, one passive and one active.

        Do you have completely (and I do mean 100% completely) different connections for the Internet and WAN connection? If they share the same cable or provider for the last mile (which is the usual case) then you are over complicating matters, as the chances are that any outage would affect both types of connections.

        However to achieve what you want to do, a script to change the proxy is about the only option. You will also need to run IISRESET for the change to take full effect.

        Simon Butler
        Exchange MVP

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