[英]Sending and receiving multicast on the same Linux machine from different interfaces
I have a network with several computers when each computer has several network interfaces with a single destination.当每台计算机都有多个网络接口和一个目标时,我有一个包含多台计算机的网络。 I'm developing an application that actively uses multicast.
我正在开发一个积极使用多播的应用程序。 In general everything works as expected.
一般来说,一切都按预期工作。 Except for the moment that I cannot receive a multicast on the same machine from which I'm sending via a second network interface.
除了我无法在我通过第二个网络接口发送的同一台机器上接收多播的那一刻。 Other computers on the network can receive multicast through any network interface.
网络上的其他计算机可以通过任何网络接口接收多播。 Is it possible to send a multicast through one interface and receive it through another within the same network?
是否可以通过一个接口发送多播并通过同一网络内的另一个接口接收它? If so, where did I make a mistake: in the client code, in the recipient code, or in the system settings?
如果是这样,我在哪里犯了错误:在客户端代码、收件人代码或系统设置中?
A typical machine configuration:典型的机器配置:
$ ifconfig
enp0s31f6: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.88.230 netmask 255.255.255.0 broadcast 192.168.88.255
enp10s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.88.229 netmask 255.255.255.0 broadcast 192.168.88.255
wlp6s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.88.48 netmask 255.255.255.0 broadcast 192.168.88.255
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
Routing table:路由表:
$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.88.1 0.0.0.0 UG 100 0 0 enp0s31f6
0.0.0.0 192.168.88.1 0.0.0.0 UG 101 0 0 enp10s0
0.0.0.0 192.168.88.1 0.0.0.0 UG 600 0 0 wlp6s0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 enp0s31f6
192.168.88.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s31f6
192.168.88.0 0.0.0.0 255.255.255.0 U 101 0 0 enp10s0
192.168.88.0 0.0.0.0 255.255.255.0 U 600 0 0 wlp6s0
These combinations work as expected这些组合按预期工作
./sender 239.255.255.251 27335 192.168.88.48
./listener 239.255.255.251 27335 192.168.88.48
or或者
./sender 239.255.255.251 27335 192.168.88.229
./listener 239.255.255.251 27335 192.168.88.229
or或者
./sender 239.255.255.251 27335 192.168.88.230
./listener 239.255.255.251 27335 192.168.88.230
But these don't work:但这些不起作用:
./sender 239.255.255.251 27335 192.168.88.48
./listener 239.255.255.251 27335 192.168.88.229
or或者
./sender 239.255.255.251 27335 192.168.88.48
./listener 239.255.255.251 27335 192.168.88.230
or或者
./sender 239.255.255.251 27335 192.168.88.229
./listener 239.255.255.251 27335 192.168.88.230
For my task, I have adapted the code from several examples from https://tldp.org/HOWTO/Multicast-HOWTO-6.html对于我的任务,我从https://tldp.org/HOWTO/Multicast-HOWTO-6.html的几个示例中改编了代码
sender.c发件人.c
//
// Simple sender.c program for UDP
//
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
if (argc < 3) {
printf("Command line args should be multicast group and port\n");
printf("(e.g. for SSDP, `sender 239.255.255.250 1900 [interface_ip]`)\n");
return 1;
}
const char* group = argv[1]; // e.g. 239.255.255.250 for SSDP
const int port = atoi(argv[2]); // 0 if error, which is an invalid port
const char* source_iface = (argc == 4 ? argv[3] : NULL);
//
// create what looks like an ordinary UDP socket
//
const int fd = socket(AF_INET, SOCK_DGRAM, 0);
if (fd < 0) {
perror("socket");
return 1;
}
struct ip_mreq mreq;
memset(&mreq, 0, sizeof(mreq));
mreq.imr_interface.s_addr = source_iface ? inet_addr(source_iface) : htonl(INADDR_ANY);
if (
setsockopt(
fd, IPPROTO_IP, IP_MULTICAST_IF, (char*) &mreq, sizeof(mreq)
) < 0
){
perror("setsockopt");
return 1;
}
//
// set up destination address
//
struct sockaddr_in addr;
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(group);
addr.sin_port = htons(port);
//
// now just sendto() our destination
//
for (unsigned i = 0; ; i++) {
char buffer[64];
memset(buffer, '\0', sizeof(buffer));
snprintf(buffer, sizeof(buffer), "Hello, World! Sequence: %u", i & 0xFF);
const int nbytes = sendto(
fd,
buffer,
sizeof(buffer),
0,
(struct sockaddr*) &addr,
sizeof(addr)
);
if (nbytes < 0) {
perror("sendto");
return 1;
}
const int delay_secs = 1;
sleep(delay_secs);
}
return 0;
}
listener.c监听器.c
//
// Simple listener.c program for UDP multicast
//
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define MSGBUFSIZE 4096
int main(int argc, char *argv[])
{
if (argc < 3) {
printf("Command line args should be multicast group and port and [interface] optional\n");
printf("(e.g. for SSDP, `listener 239.255.255.250 1900 [192.168.1.1]`)\n");
return 1;
}
const char* group = argv[1]; // e.g. 239.255.255.250 for SSDP
const int port = atoi(argv[2]); // 0 if error, which is an invalid port
const char* source_iface = (argc == 4) ? argv[3] : NULL;
//
// create what looks like an ordinary UDP socket
//
const int fd = socket(AF_INET, SOCK_DGRAM, 0);
if (fd < 0) {
perror("socket");
return 1;
}
//
// allow multiple sockets to use the same PORT number
//
const u_int yes = 1;
if (
setsockopt(
fd, SOL_SOCKET, SO_REUSEADDR, (char*) &yes, sizeof(yes)
) < 0
){
perror("Reusing ADDR failed");
return 1;
}
//
// set up destination address
//
struct sockaddr_in addr;
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(group);
addr.sin_port = htons(port);
//
// bind to receive address
//
if (bind(fd, (struct sockaddr*) &addr, sizeof(addr)) < 0) {
perror("bind");
return 1;
}
//
// use setsockopt() to request that the kernel join a multicast group
//
struct ip_mreq mreq;
memset(&mreq, 0, sizeof(mreq));
mreq.imr_multiaddr.s_addr = inet_addr(group);
mreq.imr_interface.s_addr = source_iface ? inet_addr(source_iface) : htonl(INADDR_ANY);
if (
setsockopt(
fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &mreq, sizeof(mreq)
) < 0
){
perror("setsockopt");
return 1;
}
//
// now just enter a read-print loop
//
while (1) {
char msgbuf[MSGBUFSIZE];
unsigned addrlen = sizeof(addr);
int const nbytes = recvfrom(
fd,
msgbuf,
MSGBUFSIZE,
0,
(struct sockaddr *) &addr,
&addrlen
);
if (nbytes < 0) {
perror("recvfrom");
return 1;
}
msgbuf[nbytes] = '\0';
printf("from: %s message: %s\n", inet_ntoa(addr.sin_addr), msgbuf);
}
return 0;
}
tcpdump looks good for all interfaces: tcpdump 适用于所有接口:
$ sudo tcpdump -i wlp6s0 -s0 -vv host 239.255.255.251
tcpdump: listening on wlp6s0, link-type EN10MB (Ethernet), capture size 262144 bytes
18:03:40.547226 IP (tos 0x0, ttl 1, id 55512, offset 0, flags [DF], proto UDP (17),
length 92)
i7-6700k-system.48397 > 239.255.255.251.27335: [udp sum ok] UDP, length 64
18:03:41.547602 IP (tos 0x0, ttl 1, id 55691, offset 0, flags [DF], proto UDP (17),
length 92)
i7-6700k-system.48397 > 239.255.255.251.27335: [udp sum ok] UDP, length 64
$ sudo tcpdump -i enp0s31f6 -s0 -vv host 239.255.255.251
tcpdump: listening on enp0s31f6, link-type EN10MB (Ethernet), capture size 262144 bytes
18:07:42.639153 IP (tos 0x0, ttl 1, id 20849, offset 0, flags [DF], proto UDP (17),
length 92)
i7-6700k-system.48397 > 239.255.255.251.27335: [udp sum ok] UDP, length 64
18:07:43.639911 IP (tos 0x0, ttl 1, id 20997, offset 0, flags [DF], proto UDP (17),
length 92)
i7-6700k-system.48397 > 239.255.255.251.27335: [udp sum ok] UDP, length 64
$ sudo tcpdump -i enp10s0 -s0 -vv host 239.255.255.251
tcpdump: listening on enp10s0, link-type EN10MB (Ethernet), capture size 262144 bytes
18:08:57.666159 IP (tos 0x0, ttl 1, id 30039, offset 0, flags [DF], proto UDP (17),
length 92)
i7-6700k-system.48397 > 239.255.255.251.27335: [udp sum ok] UDP, length 64
18:08:58.666518 IP (tos 0x0, ttl 1, id 30171, offset 0, flags [DF], proto UDP (17),
length 92)
ci7-6700k-system.48397 > 239.255.255.251.27335: [udp sum ok] UDP, length 64
In your listener, rather than binding to the multicast address, bind to INADDR_ANY
:在您的侦听器中,不是绑定到多播地址,而是绑定到
INADDR_ANY
:
struct sockaddr_in addr;
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = htons(port);
This will prevent any filtering based on the IP.这将阻止任何基于 IP 的过滤。
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