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 *);
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 *);