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在同一台Linux機器上從不同接口發送和接收組播

[英]Sending and receiving multicast on the same Linux machine from different interfaces

 原文  2021-12-29 15:37:20  4   1    c/ linux/ sockets/ udp/ multicast

問題描述

當每台計算機都有多個網絡接口和一個目標時，我有一個包含多台計算機的網絡。 我正在開發一個積極使用多播的應用程序。 一般來說，一切都按預期工作。 除了我無法在我通過第二個網絡接口發送的同一台機器上接收多播的那一刻。 網絡上的其他計算機可以通過任何網絡接口接收多播。 是否可以通過一個接口發送多播並通過同一網絡內的另一個接口接收它？ 如果是這樣，我在哪里犯了錯誤：在客戶端代碼、收件人代碼或系統設置中？

典型的機器配置：

$ 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

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

這些組合按預期工作

./sender 239.255.255.251 27335 192.168.88.48
./listener 239.255.255.251 27335 192.168.88.48

或者

./sender 239.255.255.251 27335 192.168.88.229
./listener 239.255.255.251 27335 192.168.88.229

或者

./sender 239.255.255.251 27335 192.168.88.230
./listener 239.255.255.251 27335 192.168.88.230

但這些不起作用：

./sender 239.255.255.251 27335 192.168.88.48
./listener 239.255.255.251 27335 192.168.88.229

或者

./sender 239.255.255.251 27335 192.168.88.48
./listener 239.255.255.251 27335 192.168.88.230

或者

./sender 239.255.255.251 27335 192.168.88.229
./listener 239.255.255.251 27335 192.168.88.230

對於我的任務，我從https://tldp.org/HOWTO/Multicast-HOWTO-6.html的幾個示例中改編了代碼

發件人.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;
}

監聽器.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 適用於所有接口：

$ 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

1 個解決方案

解決方案1
 0  2021-12-29 16:07:45

在您的偵聽器中，不是綁定到多播地址，而是綁定到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);

這將阻止任何基於 IP 的過濾。

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