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External DNS - Two IPs to same DNS RRS feed

  • Question

  • External DNS-

    1) We had some issue on our primary ISP due to which all the production services were down for ~4-5 hours. We have additional ISP already in place for all the VPN and outgoing traffic from data center. We are also in the process of having additional IP pool from the secondary ISP.

    The question here, is, If we define two IP for the same name, will it work in the event of failure on 1st IP.


    Tuesday, January 31, 2017 12:37 PM

All replies

  • Unless you have some sort of smart DNS load-balancing appliance (such as an F5) in front of any particular set of host names (whether they be DNS servers or otherwise) to which you are connecting and constantly checking on their health status and routing DNS traffic to the healthy one in case the other goes down, then what will happen is, 50% of the time your DNS clients will have a failure connecting to the target name, because they will be given the IP of the down host.  While 50% of the time they will succeed, and connect to the "up" host.  This is because DNS round-robin is a "poor man's" load balancing, in which it simply rotates through a list of IPs assigned to a particular name and randomizes how the IPs assigned are handed out to the requesting DNS clients, not taking into account if one of the hosts is down at that moment in time.  So the answer to your question is no, it will not work properly - it will fail 50% of the time.

    Best Regards, Todd Heron | Active Directory Consultant

    Tuesday, January 31, 2017 9:11 PM
  • Hi Shailc,

    If client has enabled DNS caching, client will query the same address of server, and it will query another address from DNS after caching expired.

    Or you could check NIC teaming for ISP connection, please check link below to understand it:

    Windows Server 2012: Creating a NIC TEAM for Load Balancing and Failover

    https://blogs.technet.microsoft.com/kevinholman/2012/06/02/windows-server-2012-creating-a-nic-team-for-load-balancing-and-failover/

    Best Regards

    John


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    Wednesday, February 1, 2017 2:49 AM
  • Thanks Todd..Apprreciate your help. It would be great help if you can suggest more solution if the

    Geographical distance. if plan to have DR redudecy with DC. I m also planning to have DR in place in case DC is down.

    Note-DR Digaster Data Center

    DC - Data center

    Wednesday, February 1, 2017 12:39 PM
  • Thanks John
    Tuesday, February 7, 2017 12:13 PM
  • Hi Shailc,

    For my test, if one of address is unreachable, it will query next address for client. please check link below to understand process of round robin:

    DNS Round Robin and Destination IP address selection

    https://blogs.technet.microsoft.com/networking/2009/04/17/dns-round-robin-and-destination-ip-address-selection/

    >>if plan to have DR redudecy with DC. I m also planning to have DR in place in case DC is down.

    You could deploy failover for DC, please contact with datacenter supporter to get effect support.

    Best Regards

    John


    Please remember to mark the replies as answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.

    Wednesday, February 8, 2017 9:05 AM