[The IPv6 feature is in beta phase and not ready for production usage.] For a GET request, this value is either 'null' or contains the LAN's /64 IPv6 CIDR block if this LAN is IPv6-enabled. For POST/PUT/PATCH requests, 'AUTO' will result in enabling this LAN for IPv6 and automatically assign a /64 IPv6 CIDR block to this LAN. If you choose the IPv6 CIDR block on your own, then you must provide a /64 block, which is inside the IPv6 CIDR block of the virtual datacenter and unique inside all LANs from this virtual datacenter. If you enable IPv6 on a LAN with NICs, those NICs will get a /80 IPv6 CIDR block and one IPv6 address assigned to each automatically, unless you specify them explicitly on the NICs. A virtual data center is limited to a maximum of 256 IPv6-enabled LANs.