我正在尝试在系统中的所有接口上侦听多播,但只响应我已收到多播数据包的情况。
我所做的是为每个接口创建一个套接字,这里就会出现问题。
当我将接口绑定到INADDR_ANY
时,它将接收所有接口的数据包并发送默认接口。如果我将端口绑定到特定接口,它将不会接收多播数据包(但它将能够在正确的接口上发送)。
我已尝试设置IP_ADD_MEMBERSHIP
或IP_MULTICAST_IF
等选项但未成功。
我认为其他选项可能是创建一个套接字来接收所有接口的所有ifs和发送器套接字,但是在这种方法中我不知道输入哪个ifs数据包...
代码示例(简化,无错误处理和内容):
创建套接字:
//here i am looping over all interfaces from getifaddrs
struct sockaddr_in *pAddr = (struct sockaddr_in *)tmp->ifa_addr;
sockets[i] = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
setsockopt(sockets[i], SOL_SOCKET, SO_REUSEADDR, &optval, sizeof optval);
mreq.imr_multiaddr.s_addr=inet_addr(MDNS_ADDRESS);
mreq.imr_interface.s_addr=pAddr->sin_addr.s_addr;
setsockopt(sockets[i], IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
setsockopt(sockets[i], IPPROTO_IP, IP_MULTICAST_IF, &pAddr, sizeof(struct in_addr));
memset(&my_addr, 0, sizeof(struct sockaddr_in));
my_addr.sin_family = AF_INET;
my_addr.sin_addr.s_addr = INADDR_ANY; //or pAddr->sin_addr.s_addr;
my_addr.sin_port = htons(port);
bind(sockets[i], (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1);
接收和发送:
recvfrom(sockfd, buf, MAXBUFLEN-1 , 0, (struct sockaddr *)&their_addr, &addr_len);
//do some magic and response (response should be a multicast too)
destination.sin_addr.s_addr = inet_addr(MULTICAST_ADDRESS);
destination.sin_family = AF_INET;
destination.sin_port = htons( port );
sendto(sockfd, buffer, len, 0, (struct sockaddr *)&destination, sizeof destination);
我想在mDNS的工作中创建类似的东西,所以当在特定接口程序上输入的数据包应该回答相同的情况,如果有关于此的一些数据if。它不应该在其他ifs上发送,因为它可能与它们无关,但它应该以多播方式发送,因此同一网络中的任何其他主机都将收到响应。
答案 0 :(得分:3)
你应该只需要一个插座。
首先绑定到INADDR_ANY
和您选择的端口。然后在要接收多播的每个接口上使用setsockopt
调用IP_ADD_MEMBERSHIP
。最后,在要发送多播的接口上使用setsockopt
调用IP_MULTICAST_IF
。请务必检查每次通话时的错误。
int socket s;
struct sockaddr_in sin;
struct ip_mreq mreq;
struct in_addr out_addr;
bzero(&sin,sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr=htonl(INADDR_ANY);
sin.sin_port = htons(1044); // or whatever port you listen on
if ((s = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("socket failed");
exit(1);
}
if (bind(s, (struct sockaddr *)&sin, sizeof(sin))==-1) {
perror("bind failed");
exit(1);
}
// Do this in a loop for each interface
mreq.imr_multiaddr = inet_addr("230.4.4.1"); // your multicast address
mreq.imr_interface = inet_addr("192.168.1.1"); // your incoming interface IP
if (setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&mreq, sizeof(mreq)) == -1) {
perror("Error joining multicast group");
exit(1);
}
out_addr.s_addr = inet_addr("192.168.1.1"); // your outgoing interface IP
if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, (char *)&out_addr,sizeof(out_addr))== -1) {
perror("Error setting outgoing interface");
exit(1);
}
使用多播时,应始终绑定到INADDR_ANY地址。如果不这样做会破坏Linux系统上的多播。
答案 1 :(得分:2)
最初,我接受了@dbush的答案,因为它让我能够走上正轨。为了完整起见,我发布了更详细的答案,并且按照他的建议,我接受了我自己的答案。
部分代码可在此处找到:Setting the source IP for a UDP socket
我能够通过单插槽并设置IP_PKTINFO来完成所有这些操作。
代码示例(简化,无错误处理和内容):
创建套接字:
if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP)) == -1) {
perror("socket");
exit(1);
}
if(setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof optval) < 0) {
perror("setsockopt");
exit(1);
}
optval2 = 1;
if(setsockopt(sockfd, IPPROTO_IP, IP_PKTINFO, &optval2, sizeof(optval2)) < 0) {
perror("setsockopt");
exit(1);
}
memset(&my_addr, 0, sizeof(struct sockaddr_in));
my_addr.sin_family = AF_INET;
my_addr.sin_addr.s_addr = INADDR_ANY;
my_addr.sin_port = htons(5353);
if (bind(sockfd, (struct sockaddr *)&my_addr,
sizeof(struct sockaddr)) == -1) {
perror("bind");
exit(1);
}
接收和回复:
char buf[MAXBUFLEN];
char cmsgbuf[MAXBUFLEN];
struct iovec iov[1];
iov[0].iov_base=buf;
iov[0].iov_len=sizeof(buf);
struct cmsghdr *cmsg;
struct msghdr message;
message.msg_name=&their_addr;
message.msg_namelen=sizeof(their_addr);
message.msg_iov=iov;
message.msg_iovlen=1;
message.msg_control=cmsgbuf;
message.msg_controllen=MAXBUFLEN;
if ((numbytes = recvmsg(sockfd, &message, 0)) == -1) {
perror("recvfrom");
exit(1);
}
for (cmsg = CMSG_FIRSTHDR(&message); cmsg != NULL; cmsg = CMSG_NXTHDR(&message, cmsg)) {
// ignore the control headers that don't match what we want
if (cmsg->cmsg_level != IPPROTO_IP ||
cmsg->cmsg_type != IP_PKTINFO)
{
continue;
}
struct in_pktinfo *pi = CMSG_DATA(cmsg);
addr = pi->ipi_spec_dst.s_addr;
}
//DO SOME MAGIC
//HERE WE ARE SETTING ADDR - INTERFACE WITH THIS ADDR WILL SEND MULTICAST
sock_opt_addr.s_addr = addr;
setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_IF, &sock_opt_addr, sizeof(sock_opt_addr));
sendto(sockfd, buffer, len, 0, (struct sockaddr *)&destination, sizeof destination);