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}}
+
extern type host;
{{A hostname; that is, (more or less) an alphanumeric string}}
extern val ip_of_node : node -> ip;
{{Look up the IP address of a node.}}
+extern val ipv6_of_node : node -> ipv6;
+{{Look up the IPv6 address of a node.}}
+
extern type user;
extern type group;
{{UNIX users and groups}}