+extern type ipv6;
+{{An IPv6 address}}
+
+extern type your_ip;
+extern val your_ip_to_ip : your_ip -> ip;
+{{An IP address that you're authorized to use; e.g., for an SSL web host}}
+
+extern type your_ipv6;
+extern val your_ipv6_to_ipv6 : your_ipv6 -> ipv6;
+{{An IPv6 address that you're authorized to use; e.g., for an SSL web host}}