1 /* vi: set sw=4 ts=4: */
5 * Mostly stolen from: dhcpcd - DHCP client daemon
6 * by Yoichi Hariguchi <yoichi@fore.com>
9 #include <netinet/if_ether.h>
10 #include <net/if_arp.h>
18 uint8_t h_dest[6]; /* 00 destination ether addr */
19 uint8_t h_source[6]; /* 06 source ether addr */
20 uint16_t h_proto; /* 0c packet type ID field */
23 uint16_t htype; /* 0e hardware type (must be ARPHRD_ETHER) */
24 uint16_t ptype; /* 10 protocol type (must be ETH_P_IP) */
25 uint8_t hlen; /* 12 hardware address length (must be 6) */
26 uint8_t plen; /* 13 protocol address length (must be 4) */
27 uint16_t operation; /* 14 ARP opcode */
28 uint8_t sHaddr[6]; /* 16 sender's hardware address */
29 uint8_t sInaddr[4]; /* 1c sender's IP address */
30 uint8_t tHaddr[6]; /* 20 target's hardware address */
31 uint8_t tInaddr[4]; /* 26 target's IP address */
32 uint8_t pad[18]; /* 2a pad for min. ethernet payload (60 bytes) */
40 /* Returns 1 if no reply received */
42 int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface)
46 #define s (pfd[0].fd) /* socket */
47 int rv = 1; /* "no reply received" yet */
48 struct sockaddr addr; /* for interface name */
51 s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
53 bb_perror_msg(bb_msg_can_not_create_raw_socket);
57 if (setsockopt_broadcast(s) == -1) {
58 bb_perror_msg("cannot enable bcast on raw socket");
62 /* send arp request */
63 memset(&arp, 0, sizeof(arp));
64 memset(arp.h_dest, 0xff, 6); /* MAC DA */
65 memcpy(arp.h_source, from_mac, 6); /* MAC SA */
66 arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
67 arp.htype = htons(ARPHRD_ETHER); /* hardware type */
68 arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
69 arp.hlen = 6; /* hardware address length */
70 arp.plen = 4; /* protocol address length */
71 arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
72 memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */
73 memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
74 /* tHaddr is zero-fiiled */ /* target hardware address */
75 memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */
77 memset(&addr, 0, sizeof(addr));
78 safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
79 if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
80 // TODO: error message? caller didn't expect us to fail,
81 // just returning 1 "no reply received" misleads it.
85 /* wait for arp reply, and check it */
89 unsigned prevTime = monotonic_us();
91 pfd[0].events = POLLIN;
92 r = safe_poll(pfd, 1, timeout_ms);
96 r = read(s, &arp, sizeof(arp));
100 && arp.operation == htons(ARPOP_REPLY)
101 /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
102 /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
103 && *((uint32_t *) arp.sInaddr) == test_ip
109 timeout_ms -= (monotonic_us() - prevTime) / 1000;
110 } while (timeout_ms > 0);
114 DEBUG("%srp reply received for this address", rv ? "No a" : "A");