c - 套接字应用程序无法接收 tcpreplay 发送的数据包

Question

我的服务器会在工作日的某个时间段接收到 UDP 组播数据包。我编写了一个 c 套接字应用程序来接收这些 UDP 多播数据包。由于我的服务器只能在某个时间段接收数据包，为了测试，我用tcpdump抓包。

tcpdump -i enp0s25 -s 1600 -w /home/user/log/capture.pcap

然后，我使用 tcpreplay 重播捕获的数据包。

tcpreplay -i p1p2 --pktlen /home/user/log/capture.pcap

这是“ifconfig”输出。

 enp0s25: flags=4163<UP,BROADCAST,RUNNING,MULTICAST mtu 1500

    inet 192.168.3.6  netmask 255.255.255.0  broadcast 192.168.3.255
    inet6 2400:2410:2a41:2e00:1d6f:2fde:2436:608f  prefixlen 64  scopeid 0x0<global
    inet6 fe80::555d:f7f2:a114:51df  prefixlen 64  scopeid 0x20<link
    ether 98:90:96:a7:6f:f3  txqueuelen 1000  (Ethernet)
    RX packets 45031  bytes 50053845 (47.7 MiB)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 14129  bytes 1784865 (1.7 MiB)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
    device interrupt 20  memory 0xf9100000-f9120000  

 lo: flags=73<UP,LOOPBACK,RUNNING mtu 65536

    inet 127.0.0.1  netmask 255.0.0.0
    inet6 ::1  prefixlen 128  scopeid 0x10<host
    loop  txqueuelen 1  (Local Loopback)
    RX packets 0  bytes 0 (0.0 B)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 0  bytes 0 (0.0 B)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

 p1p1: flags=4099<UP,BROADCAST,MULTICAST mtu 1500

    ether 00:02:c9:5a:77:62  txqueuelen 1000  (Ethernet)
    RX packets 0  bytes 0 (0.0 B)
    RX errors 218  dropped 207  overruns 0  frame 0
    TX packets 0  bytes 0 (0.0 B)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

 p1p2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST mtu 1500

    inet6 fe80::2acf:23a9:3c1a:89a0  prefixlen 64  scopeid 0x20<link
    ether 00:02:c9:5a:77:63  txqueuelen 1000  (Ethernet)
    RX packets 0  bytes 0 (0.0 B)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 329583  bytes 50655424 (48.3 MiB)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

 p4p1: flags=4099<UP,BROADCAST,MULTICAST mtu 1500

    ether 00:0f:53:29:e9:30  txqueuelen 1000  (Ethernet)
    RX packets 0  bytes 0 (0.0 B)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 0  bytes 0 (0.0 B)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
    device interrupt 26  

 p4p2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST mtu 1500

    ether 00:0f:53:29:e9:31  txqueuelen 1000  (Ethernet)
    RX packets 329583  bytes 51973756 (49.5 MiB)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 0  bytes 0 (0.0 B)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
    device interrupt 35

我的服务器安装了三个网卡。其中两个是光纤 channel 网卡。他们每个人都有两个端口。 p1p1和p1p2是同一个物理网卡，p4p1和p4p2是同一个物理网卡。 我将光缆从 p1p2 连接到 p4p2，因此 tcpreplay 应该将数据包从 p1p2 发送到 p4p2。

然后，我检查了是否有数据包进入 p4p2。

tcpdump -i p4p2 -nnn

部分输出:

18:05:21.062023 IP 10.10.31.31.3131 > 239.239.31.31.3131: UDP, length 97
18:05:21.062035 IP 10.10.31.31.3131 > 239.239.31.31.3131: UDP, length 97

似乎 tcpreplay 确实将捕获的数据包重新发送到 p4p2。但问题是我的 socks 应用程序无法接收这些数据包。以下是我的 C 套接字应用程序的一部分。

 #pragma  pack(1)

 #include <stdio.h>
 #include <string.h>
 #include <float.h>
 #include <stdlib.h>
 #include <ctype.h>
 #include <signal.h>
 #include <unistd.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <net/if.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/ipc.h>
 #include <sys/types.h>
 #include <sys/socket.h>


 #define MAXBUFSIZE 65536 // Max UDP Packet size is 64 Kbyte

 int main() {
     int sock, status, socklen;
     uint8_t buffer[MAXBUFSIZE];
     struct sockaddr_in saddr;
     struct ip_mreq imreq;

     memset(&saddr, 0x00, sizeof(saddr));
     memset(&imreq, 0x00, sizeof(imreq));
     memset(buffer, 0x00, MAXBUFSIZE);

     // open a UDP socket
     sock = socket(PF_INET, SOCK_DGRAM, 0);
     if ( sock < 0 ) {
         perror("Error creating socket"); 
         return(0);
     }

     imreq.imr_multiaddr.s_addr = inet_addr("239.239.31.31");
     imreq.imr_interface.s_addr = htonl(INADDR_ANY); // use DEFAULT interface

     // JOIN multicast group on default interface
     setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (const void *)&imreq, sizeof(struct ip_mreq));

     saddr.sin_family = AF_INET;
     saddr.sin_port = htons(3131); 
     saddr.sin_addr.s_addr = htonl(INADDR_ANY); 
     status = bind(sock, (struct sockaddr *)&saddr, sizeof(struct sockaddr_in));

     if ( status < 0 ) {
         perror("Error binding socket to interface");
         return(0);
     }

     socklen = sizeof(struct sockaddr_in);

     // receive 500 packets from socket
     int m = 0;
     for (; m < 500; m++) {
         status = recvfrom(sock, buffer, MAXBUFSIZE, 0, (struct sockaddr *)&saddr, &socklen);
         if(status < 0) {
             perror("receive error!\n");
         } else if (status > 0) {
             // DO sth usefully here.
         }              
     }

     // shutdown socket
     shutdown(sock, 2);
     // close socket
     close(sock);

     return 0;
 }

当我运行上面的应用程序时，它会在 recvfrom 函数处停止。谁能告诉我为什么我的应用程序无法接收这些数据包？

Answer 1

根据 tcpreplay 文档，不可能在同一台计算机上发送数据包:数据包在 TCP/IP 堆栈和网卡的设备驱动程序之间注入(inject)，因此运行 tcpreplay 的 TCP/IP 堆栈永远看不到数据包。尝试在同一台机器上的虚拟化环境中运行 tcpreplay，然后主机操作系统应该可以看到数据包。

引用:http://tcpreplay.synfin.net/wiki/FAQ