it seems coming from wherever you broadcasting, 127.0.0.1.
On Mon, 12 Feb 2007, Jerry Geis wrote:
I have a small program that I am broadcasting out on port 36 and attempting to receive information back.
Using "tcpdump port 36" I can see 2 devices responding to me but I get no data.
The response my program gets is:
Size IP Address Subnet MAC Address ID 20 0.0.0.0 0.0.0.0 00-00-00-00-00-00
Does someone know what I might not be doing correct? Running the same program under windows works, running it under wine on linux works it just doesnt work on linux.
I have iptables disabled at this time.
Thanks for nay suggestions.
Jerry
tcpdump -x port 36
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 08:42:49.286701 IP devcentos64.msgnet.com.36 > 255.255.255.255.36: UDP, length 20 0x0000: 4500 0030 0000 4000 4011 790b c0a8 010a E..0..@.@.y..... 0x0010: ffff ffff 0024 0024 001c ca61 4321 3039 .....$.$...aC!09 0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 08:42:49.286976 IP ecov132.msgnet.com.36 > devcentos64.msgnet.com.36: UDP, length 20 0x0000: 4500 0030 03c2 0000 8011 b2f2 c0a8 01ae E..0............ 0x0010: c0a8 010a 0024 0024 001c a0e2 4321 3039 .....$.$....C!09 0x0020: c0a8 01ae ffff 0000 0001 3cd0 67ff 0001 ..........<.g... 08:42:49.286990 IP ecov432_testing.msgnet.com.36 > devcentos64.msgnet.com.36: UDP, length 20 0x0000: 4500 0030 091a 0000 8011 ad8f c0a8 01b9 E..0............ 0x0010: c0a8 010a 0024 0024 001c b581 4321 3039 .....$.$....C!09 0x0020: c0a8 01b9 ffff ff00 0001 3cd0 5449 0001 ..........<.TI..
My program is:
int main(int argc, char *argv[]) { int error; int total = 0; int socket_handle;
enum { NMP_PORT = 36, NMP_MAGIC = 0x4321, NMP_LIST = 12345, NMP_SET_IP, NMP_SET_MASK };
typedef union { unsigned char b[4]; uint32_t v; } IPADDR;
typedef struct { unsigned char b[6]; } MACADDR;
typedef struct { unsigned short magic; unsigned short code; IPADDR ip; IPADDR mask; MACADDR mac; ushort Deviceid; } HD_NMP;
HD_NMP nmp;
struct sockaddr_in broadcast_address;
bzero((char *) &broadcast_address, sizeof(broadcast_address)); broadcast_address.sin_family = AF_INET; broadcast_address.sin_port = htons(NMP_PORT); broadcast_address.sin_addr.s_addr = inet_addr("255.255.255.255");
socket_handle = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if(socket_handle >= 0) { int byes = 1;
fd_set read_set;
struct timeval tm;
if(setsockopt(socket_handle, SOL_SOCKET, SO_BROADCAST, &byes, sizeof(byes)) >= 0) { if(bind(socket_handle, (struct sockaddr *) &broadcast_address, sizeof(broadcast_address)) < 0) { printf("bind error\n"); }
memset(&nmp, 0, sizeof(nmp)); nmp.magic = IWord(NMP_MAGIC); nmp.code = IWord(NMP_LIST); sendto(socket_handle, &nmp, sizeof(nmp), 0, (struct sockaddr*) &broadcast_address, sizeof(broadcast_address)); printf("%-4s %-15s %-15s %-17s %6s\n", "Size", "IP Address", "Subnet", "MAC Address", "ID"); while(1) { tm.tv_sec = 0; tm.tv_usec = 500000; FD_ZERO(&read_set); FD_SET(socket_handle, &read_set); error = select(socket_handle + 1, &read_set, NULL, NULL, &tm); if(error <= 0) { break; } else { char ip_str[100]; char mac_str[100]; char mask_str[100];
error = recvfrom(socket_handle, &nmp,sizeof(nmp), 0, NULL, 0);
if(error < 0) { printf("errno=%d %s\n", errno,strerror(errno)); continue; } else if(nmp.code != IWord(NMP_LIST)) { printf("unknown return\n"); continue; } else { sprintf(ip_str, "%d.%d.%d.%d ", nmp.ip.b[0], nmp.ip.b[1], nmp.ip.b[2], nmp.ip.b[3]); sprintf(mask_str, "%d.%d.%d.%d ", nmp.mask.b[0], nmp.mask.b[1], nmp.mask.b[2], nmp.mask.b[3]); sprintf(mac_str, "%02X-%02X-%02X-%02X-%02X-%02X", nmp.mac.b[0], nmp.mac.b[1], nmp.mac.b[2], nmp.mac.b[3], nmp.mac.b[4], nmp.mac.b[5]); printf(" %2d %-15s %-15s %-15s\n", error, ip_str, mask_str, mac_str);
total++; } } } }close(socket_handle); }
return(0); }
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