ip_rtaddr
ip_rtaddr(ip->ip_dst, &sro);
ia = ip_rtaddr(ip->ip_dst, ro);
ia = ip_rtaddr(ipaddr.sin_addr, NULL);
(ia = ip_rtaddr(ipaddr.sin_addr, NULL)) == NULL) {
ip_rtaddr(pkt_dst, &fwd_ro);
ip_rtaddr(struct in_addr, struct route *);