arp_op
ah->arp_op = htons(ARPOP_REQUEST);
if (ah->arp_op == htons(ARPOP_REQUEST)) {
if (ah->arp_op != htons(ARPOP_REPLY)) {
if (arp->arp_op != htons(ARPOP_REQUEST)) {
arp->arp_op = htons(ARPOP_REPLY);
if (ap->arp_op != htons(ARPOP_REVREPLY)) {
printf("bad op=0x%x\n", ntohs(ap->arp_op));
ap->arp_op = htons(ARPOP_REVREQUEST);
ntohs(ap->arp_op) != REVARP_REQUEST ||
ap->arp_op = htons(REVARP_REPLY);