sockets - 无法连接到 VPN 中的本地服务器

Question

我在多个 iOS、MacOS 中尝试过以下代码。
这是服务器代码

void *run_server(void *thread_id) {
    int server_fd, new_socket;
    struct sockaddr_in server, client;
    int opt = 1;
    int addrlen = sizeof(server);
   
    // Creating socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket");
        return NULL;
    }

    // Forcefully attaching socket to the port
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
        perror("setsockopt");
        return NULL;
    }

    server.sin_family = AF_INET;
    server.sin_addr.s_addr = ip("10.10.10.20"); // bind IP
    server.sin_port = htons(27042);
   
    // Forcefully attaching socket to the port
    if (bind(server_fd, (struct sockaddr *)&server, sizeof(server)) < 0) {
        perror("bind");
        return NULL;
    }

    if (listen(server_fd, 3) < 0) {
        perror("listen");
        return NULL;
    }

    printf("Server is running with %u:%d\n", server.sin_addr.s_addr, htons(server.sin_port));
    while (1) {
        if ((new_socket = accept(server_fd, (struct sockaddr *)&client, (socklen_t*)&addrlen))<0) {
            perror("accept");
            return NULL;
        }
    
        printf("Client connected with %u:%d\n", client.sin_addr.s_addr, client.sin_port);
    }
}

这是客户端代码

void scan(unsigned int ip, int port) {
    int sock = 0;
    struct sockaddr_in serv_addr;
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        printf("\nSocket creation error\n");
        return;
    }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(port);
    serv_addr.sin_addr.s_addr = ip;

    printf("IP %u, port %d\n", ip, port);
    int connected = connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
    if (connected != 0) {
        char errorMsg[256];
        strerror_r(errno, errorMsg, 256);
        printf("Error %s\n", errorMsg);
    }

    if (connected < 0) {
        close(sock);
        return;
    }
}

void *run_scan(void *thread_id) {
    while (1) {
        scan(ip("10.10.10.20"), 27042);
        usleep(1000000);
    }

    return NULL;
}

和主要功能

int main(int argc, const char * argv[]) {
    pthread_t thread1;
    if (pthread_create(&thread1, NULL, run_server, (void *)1)) {
        printf("Can't create thread run_server");
    }

    pthread_t thread2;
    if (pthread_create(&thread2, NULL, run_scan, (void *)2)) {
        printf("Can't create thread run_scan");
    }

    while (1) sleep(1);
    return 0;
}

问题描述:
此代码与本地 IP(DHCP 分配的 IP)一起正常工作。但是，当我连接到 VPN 并将服务器 IP 绑定(bind)到 PPP 网络接口(interface) IP 时，它是 10.10.10.20(如上面的示例代码)。我无法打开与该 IP 的连接。错误是“连接超时”。请注意，另一台主机仍然可以连接到 IP 为 10.10.10.20 的服务器。
感谢有关这种情况的任何知识共享。

Answer 1

找到了答案，基本上这是Linux内核强加的限制。
更多信息:https://www.softether.org/4-docs/1-manual/B._Troubleshooting_and_Supplemental/11.1_Troubleshooting