ipAddressType

[Network Load Balancers] The type of IP addresses used by the subnets for your load balancer. The possible values are ipv4 (for IPv4 addresses) and dualstack (for IPv4 and IPv6 addresses). You can’t specify dualstack for a load balancer with a UDP or TCP_UDP listener.

[Gateway Load Balancers] The type of IP addresses used by the subnets for your load balancer. The possible values are ipv4 (for IPv4 addresses) and dualstack (for IPv4 and IPv6 addresses).