Transitioning from one ISP to another using a multihomed web serve

Discussion in 'Windows Small Business Server' started by Orlando Bob, Jan 21, 2008.

  1. Orlando Bob

    Orlando Bob Guest

    I am about to change ISP's and would like it to have no impact on my web
    sites. Therefore I want both the new and the old external IP addresses to
    work while the DNS changes are being propagated. I currently have one
    external firewall connected to the old ISP and another connected to the new

    Initially I tried browsing to a web site through one of the new IP addresses
    but I did not get a response. If I change the default gateway address on the
    web server to the new firewall, browsing works from the new IP address but
    not from the old IP address.

    If I add a second NIC to the web server and configure this NIC to use the
    new firewall as the default gateway while leaving the old default gateway
    address on the original NIC, this works. Is this OK to do or is there a
    better solution?

    Microsoft says "It is not recommended to have multiple adapters configured
    on the same network ...If both NICs are on the same contiguous network, this
    should not be a problem as long as the default gateways are valid..."
    Orlando Bob, Jan 21, 2008
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  2. Orlando Bob

    Claus Guest

    When you talk about your "webserver", are you talking about your SBS box or
    is this a web dedicated server in your DMZ?
    Claus, Jan 21, 2008
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  3. Orlando Bob

    Orlando Bob Guest

    The web server is a separate box but it is not in a DMZ. The firewall
    forwards ports to various boxes including the web server and the SBS box
    depending on the external alias and the port.
    Orlando Bob, Jan 23, 2008
  4. Orlando Bob

    Claus Guest

    This is really not a recommended setup. You compromise security by exposing
    a webserver in your LAN and forwarding other ports to computers in your LAN.

    But that set aside, "multi-homing" a server in the same subnet is not
    something that MS will recommend but it will work (with periodic errors
    about duplicate names). That alone will not solve your problem. You also
    need to configure your websites accordingly.

    My real question is why would you want to go through that trouble as most
    registrars have "rapid propagation" in place that will propagate your new IP
    for your A records in less than an hour within the US and a few hours for
    Europe and Asia. Depending on who manages your DNS records there will be
    hardly any downtime.
    Claus, Jan 23, 2008
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