On 04/08/2015 05:32, Daniel Corbe wrote:
If nobody answers this question by the time I get home I'll try and
help; however, in the mean time I do have a couple of suggestions.
Have you tried writing the equivalent program in C using the sockets
API? IE is this a python specific problem or a sockets problem in
general?
The second thing is you may just want to try using raw sockets instead.
I verified before with ktrace, and now, following your suggestion,
rewrote it in C, and result is the same.
When I change SOCK_DGRAM->SOCK_RAW it keeps getting some other packets,
sin_port doesn't seem to matter. Also, UDP is the practically important
case.
Unless there is some reasonable explanation why ip source address can
influence reception, I believe this is a bug in kernel. And pretty
important one, because it can hurt DHCP servers.
Yuri
--- C program exhibiting the problem ---
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#define CK(func, call...) if ((call) < 0) {perror(#func); exit(1);}
int main() {
int sock, one = 1;
ssize_t count;
struct sockaddr_in sa;
char buffer[4096];
struct sockaddr_storage src_addr;
struct iovec iov[1];
iov[0].iov_base=buffer;
iov[0].iov_len=sizeof(buffer);
struct msghdr msg;
msg.msg_name=&src_addr;
msg.msg_namelen=sizeof(src_addr);
msg.msg_iov=iov;
msg.msg_iovlen=1;
msg.msg_control=0;
msg.msg_controllen=0;
CK(socket, sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))
CK(setsockopt, setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &one,
sizeof(one)))
CK(setsockopt, setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &one,
sizeof(one)))
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = htonl(INADDR_ANY);
//sa.sin_port = htons(67);
sa.sin_port = htons(1767);
CK(bind, bind(sock, (const struct sockaddr*)&sa, sizeof(sa)))
printf("Waiting for broadcast\n");
CK(recvmsg, count = recvmsg(sock, &msg, 0))
printf("Received broadcast packet: %zd bytes\n", count);
return 0;
}
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