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I have a system design where I will have a single WFC node using 2 Server 2016 boxes and a SQL Server 2019 Availability Group. I've followed instructions easily found for setting this up, such as these: https://www.sqlrx.com/steps-for-installing-sql-server-alwayson-availability-groups/

In addition I have found others who discuss how to do this with two subnets: https://www.sqlshack.com/simulating-a-multi-subnet-cluster-for-setting-up-sql-server-always-on-availability-groups-lab-setup/

I have been successful in setting the system up for two subnets as described above as it is simple and straight-forward. However, in my case, the node will sit at the nexus of 5 subnets.

I am sure we could debate the necessity (or craziness) of 5 subnets, but that is the network design. Some of these are redundant networks, but not all of them. Also, the WFC as access to the Domain Controller via 3 of these subnets.

The intention is to provide clients across all 5 subnets access to the AG. It seems like I could potentially add networks by extending the instructions for adding a second subnet, but I wanted to make sure that this would be the correct way to do it. Are there any specific things I need to consider or do in order to add more subnets and make the listener available to clients on each of the subnets? Should I do this at build time or after the system is functioning with 1 or 2 subnets configured?

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  • I'm not sure I understand your question. Are you asking if an AG can work with 5 subnets?
    – Sean Gallardy
    Commented Jan 31, 2023 at 19:57
  • Hi Sean, I may not have been clear. I was assuming it would work with 5 subnets, I am really looking for either confirmation on the right way to do it as I'm not confident in the right way to go about it.
    – DaveJM
    Commented Feb 1, 2023 at 3:33

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Are there any specific things I need to consider or do in order to add more subnets and make the listener available to clients on each of the subnets?

No, this should be taken care of by the networking team. If the clients can access whatever addresses are in use on the cluster, then they can access the resources of the cluster, SQL Server included. The AG will need to have an IP in the listener for each subnet that the AG could live on in the cluster, but other than that there isn't anything specific to SQL.

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  • Thanks Sean. I run into an issue when creating the cluster in that the "Access Point for Administering the Cluster" page does not allow me to configure all of the networks I have. It is at this point that I am wondering if I am thinking about this correctly. I really want clients on all 5 subnets to have access to the AG. Does it matter if the clusters' resources lists out all 5 networks?
    – DaveJM
    Commented Feb 6, 2023 at 19:38
  • The CNO (access point for the cluster) is required to have an IP from every subnet. It needs to be able to live on any node. Clients being able to communicate with the cluster is completely different than cluster resources itself.
    – Sean Gallardy
    Commented Feb 6, 2023 at 21:57
  • Thank you! I realized that nearly all of my subnets did not have a gateway IP assigned; once I did that, they appeared correctly. Thank you again!
    – DaveJM
    Commented Feb 7, 2023 at 13:39

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