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NLB in Unicast mode does not work

    Question

  • Hi,

    we have 4 servers (Windows Server 2012 R2) based on VMware which should be in a Windows NLB-Cluster.

    Each server has only one NIC. An A-record is available in DNS.

    The installation and configuration of NLB worked. But if the NLB bases on Unicast, then no communication is possible between the servers. When we switch NLB to Multicast, then the communication is possible. Microsoft writes, if NLB is in Unicast mode, then a registry record named UnicastInterHostCommSupport should be exist. It exists also on the servers.

    Any idea and solution?

    Best Regards

    Birdal


    • Edited by _Birdal Wednesday, February 08, 2017 3:54 PM
    Wednesday, February 08, 2017 3:38 PM

Answers

  • Hi all,

    we have decided NLB on multicast network and deployed it successful.

    Best Regards

    Birdal

    • Marked as answer by _Birdal Monday, May 08, 2017 8:04 AM
    Monday, May 08, 2017 8:03 AM

All replies

  • Hi Birdal,

    When NLB's model is unicast, adapter did not have its own MAC address, it have virtual address for NLB.

    For more information, please check link below for further understanding:

    Balancing Act – What you really ought to know about Windows Server NLB

    https://blogs.technet.microsoft.com/networking/2008/12/09/balancing-act-what-you-really-ought-to-know-about-windows-server-nlb/

    Best Regards

    John


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    Thursday, February 09, 2017 2:55 AM
  • Hi,

    we have found the problem.

    NLB in multicast mode in a VMware environment ist not possible without ESX host configuration:

     https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1556

    Because of that we deployed NLB in multicast mode.

    The servern defined in NLB can communicate each other, with other servers in the same subnet and in the other subnets..

    The computers from other subnets can also communicate with the servers in NLB.

    PROBLEM?!:

    The computers from other subnets cannot ping / cannot reach A record in DNS for NLB.

    Any idea?

    Best Regards

    Birdal


    • Edited by _Birdal Thursday, February 09, 2017 9:06 AM
    Thursday, February 09, 2017 9:05 AM
  • Hi Birdal,

    >>The computers from other subnets can also communicate with the servers in NLB.

    Did you mean that computers could ping servers in NLB by IP address?

    >>The computers from other subnets cannot ping / cannot reach A record in DNS for NLB.

    Were all of computers occurred the same issue?

    Please check if connection between DNS server, and then please run nslookup command to check if fqdn of NLB is correct.

    Please flush DNS server cache and check again.

    Best Regards

    John


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    Friday, February 10, 2017 7:11 AM
  • Hi Jon,

    I think the problem is multicast in NLB.

    We will first configure a speical vLAN for SCOM servers and make the network for the multicast free.

    After that I will test NLB again.

    Best Regards

    Birdal

    Monday, February 13, 2017 11:52 AM
  • Hi Birdal,

    Please ensure there is ARP entry exist on switch.

    Best Regards

    John


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    Tuesday, February 14, 2017 12:39 PM
  • Hi John,

    yes, I must be sure that ARP lists exist on switches.

    Best Regards

    Birdal

    Wednesday, February 15, 2017 8:52 AM
  • Hi Birdal,

    Have you resolved successfully issue?

    If there is anything we can do for you, please feel free to post it in the forum.

    Best Regards

    John


    Please remember to mark the replies as answers if they help.
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    Wednesday, February 22, 2017 7:06 AM
  • Hi John,

    it will take some time until we have test network environment for it. After that I can say if the problem is solved.

    Best Regards

    Birdal 


    • Edited by _Birdal Thursday, February 23, 2017 9:55 AM
    Thursday, February 23, 2017 9:54 AM
  • Hi Birdal,

    Thanks for your effort and understanding.

    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.

    Friday, February 24, 2017 9:15 AM
  • Hi all,

    we have decided NLB on multicast network and deployed it successful.

    Best Regards

    Birdal

    • Marked as answer by _Birdal Monday, May 08, 2017 8:04 AM
    Monday, May 08, 2017 8:03 AM