Announcement

Collapse
No announcement yet.

Help with DNS for intranet (primary and backup web server)

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Help with DNS for intranet (primary and backup web server)

    I"m hoping some experts can provide some help for an IIS web site novice who has been handed a task that isn't in my normal job function.

    We have 2 intranet web servers, a primary and a backup that we want our users to access. If the primary is down we'd like to auto direct them to the backup. We have a DNS server on our network. All three servers are running 2008 R2

    Server names:
    DNS
    Primary_Web
    Backup_Web

    In the browser we want them to type: Blaze.net and to be directed to Primary_Web, if the primary isn't there we want them to be automatically sent to Backup_Web

    I know the simple thing is to just type the server name in the browser and add bookmarks for both but the boss doesn't want that, he wants to type Blaze.net and let the DNS server figure out where to send them

    Any help and examples would be appreciated!!

  • #2
    Re: Help with DNS for intranet (primary and backup web server)

    Hi Pennyfan01,

    Sorry but DNS can't do this. DNS can sort of do load balancing with round robin and netmask ordering but it doesn't know when a host is down.

    I would look at using NLB.
    http://technet.microsoft.com/en-us/l.../hh831698.aspx
    Regards,
    Jeremy

    Network Consultant/Engineer
    Baltimore - Washington area and beyond
    www.gma-cpa.com

    Comment


    • #3
      Re: Help with DNS for intranet (primary and backup web server)

      Thanks for the info, I Will look at the load balancing.

      Right now I have set two A records in DNS with the identical name and each points to one of the intranet servers. So far when I disconnect the primary web server from the network and a you enter the name I used for the A Records it does bring up the intranet site on the backup server. This seems to work and I think will suffice for our needs, is there something I might be missing where this may not work in the long run?

      Comment


      • #4
        Re: Help with DNS for intranet (primary and backup web server)

        It may seem like it's working but a deeper understanding of DNS is needed. The DNS server will hand out the two records in a round robin.

        e.g.
        DNS server has two A records for blaze.net. One with IP1 and one with IP2

        - client1 asks DNS server for blaze.net
        - DNS server gives client1 record that points to IP address1
        - client2 asks DNS server for blaze.net
        - DNS server gives client2 record that points to IP address2
        - client3 asks DNS server for blaze.net
        - DNS server gives client3 record that points to IP address1
        - client4 asks DNS server for blaze.net
        - DNS server gives client4 record that points to IP address2
        etc, etc.

        So this is done and then one of the servers goes down. Half the clients will be accessing the server that is still up and half will be trying to access the downed server.

        I should also note that there is a TTL value on the records the clients receive. The TTL tells the client when it needs to request a new record. The TTL is usually a few hours so the clients won't ask for a new record until the TTL expires. This means that clients will have the right or wrong record until the TTL expires and then it's the luck of the draw again when it requests a new record from the DNS server.

        This is why DNS does not handle fault tolerance but sort of does load balancing. NLB is fault tolerant because it virtualizes the IP address you connect to and manages the connections without the client having to know which server it is connecting to.

        Hopefully that helps clarify things. Let me know if you have any questions.
        Last edited by JeremyW; 30th November 2012, 03:55. Reason: typos
        Regards,
        Jeremy

        Network Consultant/Engineer
        Baltimore - Washington area and beyond
        www.gma-cpa.com

        Comment


        • #5
          Re: Help with DNS for intranet (primary and backup web server)

          As JeremyW has stated, NLB or another load balancing method is needed. DNS round robin doesn't have the intelligence to know when one of the servers is down and will happily resolve client queries to the down server. NLB, which works at layer 3, knows when one of the servers is down at layer 3 and won't route connections to that server. If you need application layer load balancing awareness then you'll need something that load balances at layer 7.

          Comment


          • #6
            Re: Help with DNS for intranet (primary and backup web server)

            Guys, Thanks for the help, i'm getting a much better understanding of DNS form your responses.

            I was going to try and configure an ARR Server Farm (saw this solution on technet) If I create that on one of the servers and it genrates me a virtual IP to use in my DNS A Record what happens if the server where I created the from is the one that drops? Does this farm replicate onto both?

            Am I on the right pathe with the ARR Server Farm?

            Comment


            • #7
              Re: Help with DNS for intranet (primary and backup web server)

              I've never used ARR but it looks like the health check monitoring component of ARR might do the trick for you.

              Comment


              • #8
                Re: Help with DNS for intranet (primary and backup web server)

                Forget the ARR Server farm... Network Load balancing turned on, both servers in that cluster, one DNS A record pointing to the cluster's IP. All seems to work as desired. Thanks both of you for your help

                Comment


                • #9
                  Re: Help with DNS for intranet (primary and backup web server)

                  Glad to help
                  Regards,
                  Jeremy

                  Network Consultant/Engineer
                  Baltimore - Washington area and beyond
                  www.gma-cpa.com

                  Comment

                  Working...
                  X