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Window NLB in Exchange 2013 DR site

    Question

  • My company has Exchange 2013 in 2 sites, a primary site and also a DR site. In the primary site we have 2 MB servers and 3 CAS servers. We are using WNLB to load balance the CAS servers in the primary site. They don't have money for a hardware LB right now but we need to complete the DR plan. In the DR site there is 1 MB server and 2 CAS servers. I tried adding the DR CAS server to the NLB but I don't believe that the NLB will communicate across subnets. So, my next though is to create another WNLB in the DR site and in the event we lose our primary site we would simply change external translation and internal DNS to point to the NLB in the DR site. I know this is a poor man's fix but all I have with no hardware NLB. I guess my question is will this work?  Any responses appreciated. 
    Tuesday, April 17, 2018 2:41 PM

Answers

  • Windows Network Load Balancing (WNLB) is a common software load balancer used for Exchange servers. There are several limitations associated with deploying WNLB with Microsoft Exchange.

    • WNLB can't be used on Exchange servers where mailbox DAGs are also being used because WNLB is incompatible with Windows failover clustering. If you're using an Exchange 2013 DAG and you want to use WNLB, you need to have the Client Access server role and the Mailbox server role running on separate servers.

    • WNLB doesn't detect service outages. WNLB only detects server outages by IP address. This means that if a particular web service, such as Outlook Web App, fails, but the server is still functioning, WNLB won’t detect the failure and will still route requests to that Client Access server. Manual intervention is required to remove the Client Access server experiencing the outage from the load balancing pool.

    • Using WNLB can result in port flooding, which can overwhelm networks.

    • Because WNLB only performs client affinity using the source IP address, it's not an effective solution when the source IP pool is small. This can occur when the source IP pool is from a remote network subnet or when your organization is using network address translation.

    Please check you have all prereq above before implementing NLB.


    Please mark as helpful if you find my contribution useful or as an answer if it does answer your question. That will encourage me - and others - to take time out to help you. Thank you! Off2work

    Tuesday, April 17, 2018 5:00 PM

All replies

  • Windows Network Load Balancing (WNLB) is a common software load balancer used for Exchange servers. There are several limitations associated with deploying WNLB with Microsoft Exchange.

    • WNLB can't be used on Exchange servers where mailbox DAGs are also being used because WNLB is incompatible with Windows failover clustering. If you're using an Exchange 2013 DAG and you want to use WNLB, you need to have the Client Access server role and the Mailbox server role running on separate servers.

    • WNLB doesn't detect service outages. WNLB only detects server outages by IP address. This means that if a particular web service, such as Outlook Web App, fails, but the server is still functioning, WNLB won’t detect the failure and will still route requests to that Client Access server. Manual intervention is required to remove the Client Access server experiencing the outage from the load balancing pool.

    • Using WNLB can result in port flooding, which can overwhelm networks.

    • Because WNLB only performs client affinity using the source IP address, it's not an effective solution when the source IP pool is small. This can occur when the source IP pool is from a remote network subnet or when your organization is using network address translation.

    Please check you have all prereq above before implementing NLB.


    Please mark as helpful if you find my contribution useful or as an answer if it does answer your question. That will encourage me - and others - to take time out to help you. Thank you! Off2work

    Tuesday, April 17, 2018 5:00 PM
  • Hi,

    Just checking in to see if above information was helpful. Please let us know if you would like further assistance.

    Regards,

    Manu Meng


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

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Thursday, April 19, 2018 2:18 AM
    Moderator
  • Hi,

    It has been a long time since you made the last post on this thread. If you could get any help from the above posts, please be free to mark them as answers, it will be helpful to troubleshoot the similar issue and provide convenience for others to find the answers.

    Regards,

    Manu Meng


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

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Saturday, April 28, 2018 1:13 PM
    Moderator