+extern struct ip_nat_protocol *ip_nat_proto_find_get(u_int8_t protocol);
+extern void ip_nat_proto_put(struct ip_nat_protocol *proto);
+
+/* Built-in protocols. */
+extern struct ip_nat_protocol ip_nat_protocol_tcp;
+extern struct ip_nat_protocol ip_nat_protocol_udp;
+extern struct ip_nat_protocol ip_nat_protocol_icmp;
+extern struct ip_nat_protocol ip_nat_unknown_protocol;
+