[CentOS] playing with SO_BROADCAST on centos

[Hiep Nguyen]

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.. at .@.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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