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Load Balancing Email across 2 internet Links

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  • Load Balancing Email across 2 internet Links

    Hello
    Not sure if this falls into the Exchange category but since it was related to email I thought I would post it here.

    Would be grateful if anyone could help me out in this matter.

    I currently have two internet links. Email is currently configured to come and go on the one internet link (link1). I would like to load balance it across link1 and link2 in other words if either of the links fail there should be no disruption in email flow.

    Currently the MX records point to a public IP provided by the ISP of link1 and natted internally to our SMTP gateway which in turn talks to our Exchange server.

    Can I Nat a public IP provided by the ISP of link2 to the same internal IP belonging to the SMTP gateway and then set an MX record with the same priority to the link2 public IP?

    Any suggestions or working configs are most welcome

    -Thanks in Advance
    Raj

  • #2
    Re: Load Balancing Email across 2 internet Links

    Inbound email doesn't matter. Exchange couldn't care less where the email came in. Therefore you could put the IP address of the second connection in as an extra MX record and email would continue to come in.

    Outbound email will be a little more complicated.

    Where do your links come in? Are they terminating on the Exchange server itself (so it has two NICs) or does a router terminate the links and everything inside has a single gateway?

    If you are using the single gateway method, and are not using a smart host, then you shouldn't have too much of a problem. Make sure that the second IP address has a reverse DNS record. The only issue will be that the SMTP banner from the Exchange server when sending will be different when using the "other" link, but there isn't really much you can do about that. The Exchange server cannot have two identity's, Exchange routes email based on destination, nothing more.

    If you are using two NICs on the Exchange server then I recommend that you switch to a router that supports dual WAN connections and let the router sort it out.

    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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    • #3
      Re: Load Balancing Email across 2 internet Links

      Hiya, Thanks for the response.

      I have both the links terminating on a Cisco router with the LAN pointing to a single default gateway which is nothing but the ethernet address giving to the router.

      I would assume the MX record priority will be the same as the other one.

      Comment


      • #4
        Re: Load Balancing Email across 2 internet Links

        Priority on the MX records is up to you.
        You have them the same, you could adjust their weight.
        If you have a connection that is under-utilised then you could use that for inbound email.
        As long as you have both servers in the MX records the internet will use both.

        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.

        Comment


        • #5
          Re: Load Balancing Email across 2 internet Links

          Okie Doke..Sounds good. Thanks a lot

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