-extern char *net2str(subnet_t *);
-extern subnet_t *str2net(char *);
-extern int subnet_compare(subnet_t *, subnet_t *);
-extern subnet_t *lookup_subnet(struct node_t *, subnet_t *);
-extern subnet_t *lookup_subnet_mac(mac_t *);
-extern subnet_t *lookup_subnet_ipv4(ipv4_t *);
-extern subnet_t *lookup_subnet_ipv6(ipv6_t *);
+extern char *net2str(const subnet_t *);
+extern subnet_t *str2net(const char *);
+extern subnet_t *lookup_subnet(const struct node_t *, const subnet_t *);
+extern subnet_t *lookup_subnet_mac(const mac_t *);
+extern subnet_t *lookup_subnet_ipv4(const ipv4_t *);
+extern subnet_t *lookup_subnet_ipv6(const ipv6_t *);