ifa_ifwithnet
struct ifaddr *ifa_ifwithnet(struct sockaddr *);
if ((ifa = ifa_ifwithnet(gateway)) == NULL) {
ifa = ifa_ifwithnet(gateway);
ifa = ifa_ifwithnet(ifpaddr);
ia = ifatoia(ifa_ifwithnet(sintosa(sin)));
ia = (INA)ifa_ifwithnet((SA)&ipaddr);
(ia = ifatoia(ifa_ifwithnet(sintosa(dst)))) == NULL) {