c - C Linux 的数据包路由器。设置发送到()

Question

我正在尝试制作一个数据包路由器来接收数据包、读取其目的地并在途中发送它。它接收数据包很好，问题是当我尝试执行 sendto() 时，我总是收到错误

sendto() failed: No such device or address

我正在从接收到的数据包的以太网 header 中获取目标 MAC 地址，将其加载到 struct sockaddr_ll 并将其传递给 sendto() 但它不是不工作。

此外，当我将一台主机 ping 到另一台主机时，我的打印语句输出的源 ip 为 40.41.42.43，目标 ip 为 44.45.46.47，并且这些设备都不存在。我是否正确读取了以太网和 IP header ？或者套接字可能以某种方式弄乱了？

无论如何，这是代码。

int main(int argc, char *argv[])
{
int sock1, sock2, sock3;
int status = 0;
fd_set readfds;
int buffer[256];
int socknum = 0;




// Create 3 sockets
if ((sock1 = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0){
    perror("socket() failed");
    exit(1);
}
if ((sock2 = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0){
    perror("socket() failed");
    exit(1);
}
if ((sock3 = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0){
    perror("socket() failed");
    exit(1);
}
// Bind sockets to interfaces
struct ifreq ifr;
memset(&ifr, 0, sizeof(ifr));
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "r0-eth1");
if (setsockopt(sock1, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0) {
perror("setsockopt() inf config failed");
exit(1);
}
memset(&ifr, 0, sizeof(ifr));
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "r0-eth2");
if (setsockopt(sock2, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0) {
perror("setsockopt() inf config failed");
exit(1);
}
memset(&ifr, 0, sizeof(ifr));
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "r0-eth3");
if (setsockopt(sock3, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0) {
perror("setsockopt() inf config failed");
exit(1);
}

printf("All sockets bound to interfaces.\n");


while(1)
{
    //Setup select
    FD_ZERO(&readfds);
    FD_SET(sock1, &readfds);
    FD_SET(sock2, &readfds);
    FD_SET(sock3, &readfds);
    printf("Sockets set to read.\n");

    struct timeval tv = {2, 0};

    printf("Starting select.\n");
    status = select( sock3 + 1, &readfds , NULL , NULL , &tv );
    printf("status = %d\n", status);

    struct sockaddr_in sockAddr;
    socklen_t sockLen = sizeof(sockAddr);
    memset(&sockAddr, 0, sockLen);
    sockAddr.sin_family = AF_INET;
    sockAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    int bufLen = 0;


    // Check select
    if (status > 0) {
        printf("status = %d, preparing to read.\n", status);
        // Read IP datagram (d) 
        if (FD_ISSET(sock1, &readfds)) {
            printf("Socket 1 ready to receive.\n");
            printf("Attempting to receive packet.\n");
            bufLen = recvfrom(sock1, buffer, 65535, 0, (struct sockaddr *) &sockAddr, (socklen_t *)&sockLen);
            printf("Received packet.\n");
            socknum = 1;
        }
        else if (FD_ISSET(sock2, &readfds)) {
            printf("Socket 2 ready to receive.\n");
            printf("Attempting to receive packet.\n");
            bufLen = recvfrom(sock2, buffer, 65535, 0, (struct sockaddr *) &sockAddr, (socklen_t *)&sockLen);
            printf("Received packet.\n");
            socknum = 2;
        }
        else if (FD_ISSET(sock3, &readfds)) {
            printf("Socket 3 ready to receive.\n");
            printf("Attempting to receive packet.\n");
            bufLen = recvfrom(sock3, buffer, 65535, 0, (struct sockaddr *) &sockAddr, (socklen_t *)&sockLen);
            printf("Received packet.\n");
            socknum = 3;
        }
        printf("Testing Packet.\n");

        struct ethhdr *eth = (struct ethhdr *)(buffer);
        printf("\nEthernet Header\n");
        printf("\t|-Source Address : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X\n",eth->h_source[0],eth->h_source[1],eth->h_source[2],eth->h_source[3],eth->h_source[4],eth->h_source[5]);
        printf("\t|-Destination Address : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X\n",eth->h_dest[0],eth->h_dest[1],eth->h_dest[2],eth->h_dest[3],eth->h_dest[4],eth->h_dest[5]);
        printf("\t|-Protocol : %d\n",eth->h_proto);


        // Inspect IP (e)
        unsigned short iphdrlen;
        struct sockaddr_in source;
        struct sockaddr_in dest;
        struct iphdr *ip = (struct iphdr*)(buffer + sizeof(struct ethhdr));
        memset(&source, 0, sizeof(source));
        source.sin_addr.s_addr = ip->saddr;
        memset(&dest, 0, sizeof(dest));
        dest.sin_addr.s_addr = ip->daddr;

        printf("\t|-Version : %d\n",(unsigned int)ip->version);
        printf("\t|-Internet Header Length : %d DWORDS or %d Bytes\n",(unsigned int)ip->ihl,((unsigned int)(ip->ihl))*4);
        printf("\t|-Type Of Service : %d\n",(unsigned int)ip->tos);
        printf("\t|-Total Length : %d Bytes\n",ntohs(ip->tot_len));
        printf("\t|-Identification : %d\n",ntohs(ip->id));
        printf("\t|-Time To Live : %d\n",(unsigned int)ip->ttl);
        printf("\t|-Protocol : %d\n",(unsigned int)ip->protocol);
        printf("\t|-Header Checksum : %d\n",ntohs(ip->check));
        printf("\t|-Source IP : %s\n", inet_ntoa(source.sin_addr));
        printf("\t|-Destination IP : %s\n",inet_ntoa(dest.sin_addr));


        printf("index=%d\n",ifreq_i.ifr_ifindex);

        // Pull the address from the ethernet header.
        struct sockaddr_ll addr;
        memset(&addr, 0, sizeof(struct sockaddr_ll));
        addr.sll_family = AF_PACKET;
        addr.sll_ifindex = ifr.ifr_ifindex;
        addr.sll_halen = ETHER_ADDR_LEN;
        addr.sll_protocol = htons(0x0800);
        addr.sll_addr[0] = eth->h_dest[0];
        addr.sll_addr[1] = eth->h_dest[1];
        addr.sll_addr[2] = eth->h_dest[2];
        addr.sll_addr[3] = eth->h_dest[3];
        addr.sll_addr[4] = eth->h_dest[4];
        addr.sll_addr[5] = eth->h_dest[5];

        if(sendto(sock1, buffer, bufLen, 0, (struct sockaddr *) &addr, sizeof(addr)) < bufLen){
            perror("sendto() failed");
            exit(1);
        }
    }

感谢任何帮助。

Answer 1

我立即找到了答案，但我会保留它以防其他人遇到类似问题。在底部，当我设置 struct sockaddr_ll addr; 时。这一行:

addr.sll_ifindex = ifr.ifr_ifindex;

应该是这样的:

addr.sll_ifindex = ifreq_i.ifr_ifindex;

套接字和套接字的索引不同，因此 sendto() 无法找到适合这些参数的设备。