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ARP reply function

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Dimitri Lozeve 2016-05-26 16:54:48 +02:00
parent 64b99fc6d0
commit d1db809cdf
2 changed files with 85 additions and 0 deletions
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84
arp.c
View file

@ -89,3 +89,87 @@ int send_arp_request(int sockfd, int ifindex, struct sockaddr_in *ipaddr, unsign
return 0;
}
/* Sends an ARP reply
sockfd: file descriptor of the socket
ifindex: index of the network interface
sender_ip: source IP address
sender_mac: source MAC address
target_ip: IP address to which the answer is destined
target_mac: MAC address of the target
The function returns 0 on success, or exits with EXIT_FAILURE.
*/
int send_arp_reply(int sockfd, int ifindex, struct sockaddr_in *sender_ip, unsigned char *sender_mac, struct in_addr target_ip, unsigned char *target_mac)
{
/* DEFINITION OF THE DESTINATION */
/* The destination of the packet is contained in a struct
sockaddr_ll */
struct sockaddr_ll addr;
addr.sll_family = AF_PACKET; /* always AF_PACKET */
addr.sll_protocol = htons(ETH_P_ARP); /* physical-layer protocol */
addr.sll_ifindex = ifindex; /* interface number */
addr.sll_halen = ETHER_ADDR_LEN; /* length of address */
/* physical-layer address: */
memcpy(addr.sll_addr, target_mac, ETHER_ADDR_LEN);
#ifdef DEBUG
printf("[OK] Destination structure (struct sockaddr_ll) "
"constructed successfully\n");
#endif
/* ====================================================================== */
/* CONSTRUCTION OF THE FRAME */
/* We can now build the ARP reply frame, using the structures
defined in <netinet/if_ether.h> (included by
<netinet/ether.h>). */
struct ether_arp reply;
reply.arp_hrd = htons(ARPHRD_ETHER); /* hardware type: Ethernet */
reply.arp_pro = htons(ETH_P_IP); /* Protocol type: IP */
reply.arp_hln = ETHER_ADDR_LEN; /* Hardware address length */
reply.arp_pln = sizeof(in_addr_t); /* Protocol address length */
reply.arp_op = htons(ARPOP_REPLY); /* Operation code */
/* Target hardware address: 0 since this is one we want */
memcpy(&reply.arp_tha, target_mac, sizeof(reply.arp_tha));
/* Target protocol address: we put the IP address for which we want
the layer-2 address */
memcpy(&reply.arp_tpa, &target_ip.s_addr, sizeof(reply.arp_tpa));
/* Sender hardware address */
memcpy(&reply.arp_sha, sender_mac, sizeof(reply.arp_sha));
/* Sender protocol (IP) address */
memcpy(&reply.arp_spa, &sender_ip->sin_addr, sizeof(reply.arp_spa));
#ifdef DEBUG
printf("[OK] ARP reply structure (struct ether_arp) "
"constructed successfully\n");
#endif
/* ====================================================================== */
/* SEND THE FRAME */
int err = sendto(sockfd, &reply, sizeof(reply), 0,
(struct sockaddr *) &addr, sizeof(addr));
if (err == -1) {
perror("[FAIL] sendto()");
exit(EXIT_FAILURE);
}
#ifdef DEBUG
printf("[OK] Frame sent\n");
#endif
return 0;
}

1
arp.h
View file

@ -36,5 +36,6 @@
*/
int send_arp_request(int sockfd, int ifindex, struct sockaddr_in *ipaddr, unsigned char *macaddr, struct in_addr target_ip);
int send_arp_reply(int sockfd, int ifindex, struct sockaddr_in *sender_ip, unsigned char *sender_mac, struct in_addr target_ip, unsigned char *target_mac);
#endif /* ARP_H_ */