Associates a target network with a Client VPN endpoint. A target network is a subnet in a VPC. You can associate multiple subnets from the same VPC with a Client VPN endpoint. You can associate only one subnet in each Availability Zone. We recommend that you associate at least two subnets to provide Availability Zone redundancy.

If you specified a VPC when you created the Client VPN endpoint or if you have previous subnet associations, the specified subnet must be in the same VPC. To specify a subnet that's in a different VPC, you must first modify the Client VPN endpoint (ModifyClientVpnEndpoint) and change the VPC that's associated with it.