getnetbyaddr
struct netent *getnetbyaddr(uint32_t, int);
np = getnetbyaddr(ipa.s_addr, AF_INET);
np = getnetbyaddr(i, AF_INET);
np = getnetbyaddr((long)in.s_addr,
ne = getnetbyaddr(net, AF_INET);
np = getnetbyaddr(i >> NSHIFT(ntohl(mask)), AF_INET);