AlwaysOn Multi-Subnet Configuration

There are several ways to configure AlwaysOn, and even more ways to configure networking behind the cluster. A very common configuration I’ve setup and seen in production environment is a Active site and Passive disaster recovery site. In this scenario the cluster configuration needs the ability to bring the AlwaysOn resource online, even if it will never have the need to actually do that. Because of this you will need to assign an IP address from all subnets to the AlwaysOn group. This can potentially cause problems with DNS if all addresses are registered to the CNAME. There are some steps to overcome this here. In summary this is what action I take on my clusters:

  1. Open PowerShell with “Run as Administrator”
  2. Run command to list all clustered resources. We are focused on the AlwaysOn listener name:

  3. Run the following command to unregister the IP address that are not in use:
  4. Restart the Availability Group clustered resource.

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