ubuntu:/dev/net$ ls 
tun

#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <sys/types.h>
#include <linux/if_tun.h>
#include<stdlib.h>
#include<stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define IP_VERSION 4
#define IP_HEADER_LENGTH 20 // IPv4頭部長(zhǎng)度，單位為字節(jié)
#define DEST_IP "10.0.0.2"

struct iphdr {
    unsigned char  ihl_version;
    unsigned char  tos;
    unsigned short total_length;
    unsigned short id;
    unsigned short frag_off;
    unsigned char  ttl;
    unsigned char  protocol;
    unsigned short checksum;
    unsigned int   saddr;
    unsigned int   daddr;
};
int tun_alloc(int flags)
{
    struct ifreq ifr;
    int fd, err;
    char *clonedev = "/dev/net/tun";
    if ((fd = open(clonedev, O_RDWR)) < 0) {
        return fd;
    }
    memset(&ifr, 0, sizeof(ifr));
    ifr.ifr_flags = flags;

    if ((err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0) {
        close(fd);
        return err;
    }
    system("sudo ifconfig tun0 10.0.0.1 up");//啟動(dòng)tun虛擬網(wǎng)卡
    system("sudo route add -net 10.0.0.2 netmask 255.255.255.255 dev tun0");//將所有發(fā)送到 10.0.0.2 的數(shù)據(jù)包，通過(guò)網(wǎng)絡(luò)接口 "tun0" 進(jìn)行傳輸，而且這個(gè)目標(biāo)地址被視為一個(gè)單獨(dú)的主機(jī)，而不是一個(gè)整個(gè)網(wǎng)絡(luò)。
    system("sudo route add -net 192.168.6.1 netmask 255.255.255.255 dev tun0");
    printf("Open tun/tap device: %s for reading...\n", ifr.ifr_name);

    return fd;
}

int main()
{

            int tun_fd, nread;
            char buffer[1500];
            char buffer1[IP_HEADER_LENGTH + 100]; // IP頭部長(zhǎng)度 + 應(yīng)用層數(shù)據(jù)長(zhǎng)度        
            tun_fd = tun_alloc(IFF_TUN | IFF_NO_PI);
            if (tun_fd < 0) 
            {
            perror("Allocating interface");
            exit(1);
            }
while (1) {
            //發(fā)送數(shù)據(jù)包到TUN/TAP設(shè)備
            memset(buffer,0,sizeof(buffer));
            //讀取協(xié)議棧發(fā)送來(lái)的信息
            nread = read(tun_fd, buffer, sizeof(buffer));
            if (nread < 0) {
            close(tun_fd);
            exit(1);
            }
            printf("Read %zd bytes from tun/tap device\n", nread);
            // 以十六進(jìn)制格式輸出IP數(shù)據(jù)包
            for (int i = 0; i < nread; i++) {
            printf("%02X ", buffer[i]);
            if ((i + 1) % 16 == 0) {
            printf("\n");
            }
            }
            printf("\n");
            // 構(gòu)造 IP 數(shù)據(jù)包頭部，此處就可以進(jìn)行數(shù)據(jù)加密，具體的功能未完成，可自行加密處理
            struct iphdr *ip_header = (struct iphdr *)buffer1;
            ip_header->ihl_version = (IP_VERSION << 4) | (IP_HEADER_LENGTH / 4);
            ip_header->tos = 0;
            ip_header->total_length = htons(IP_HEADER_LENGTH + 8); // IP 頭部長(zhǎng)度 + ICMP 數(shù)據(jù)長(zhǎng)度
            ip_header->id = 0;
            ip_header->frag_off = 0;
            ip_header->ttl = 64;
            ip_header->protocol = 1;//IPPROTO_ICMPCMP 協(xié)議
            ip_header->checksum = 0; // 留空，內(nèi)核會(huì)自動(dòng)計(jì)算校驗(yàn)和
            ip_header->saddr = inet_addr("10.0.0.1"); // 源 IP 地址
            ip_header->daddr = inet_addr("14.0.0.2"); // 目標(biāo) IP 地址

            // 添加 ICMP 數(shù)據(jù)
            char *icmp_data = buffer1 + IP_HEADER_LENGTH;
            icmp_data[0] = 8; // ICMP 類(lèi)型為 8（Echo Request）
            icmp_data[1] = 0; // ICMP 代碼為 0
            icmp_data[2] = 0; // 校驗(yàn)和高位字節(jié)
            icmp_data[3] = 0; // 校驗(yàn)和低位字節(jié)
            icmp_data[4] = 0x12; // 標(biāo)識(shí)符高位字節(jié)
            icmp_data[5] = 0x34; // 標(biāo)識(shí)符低位字節(jié)
            icmp_data[6] = 0; // 序列號(hào)高位字節(jié)
            icmp_data[7] = 0; // 序列號(hào)低位字節(jié)

            // 計(jì)算 ICMP 校驗(yàn)和
            unsigned short checksum = 0;
            for (int i = 0; i < 8; i += 2) {
            checksum += (icmp_data[i] << 8) | icmp_data[i + 1];
            }
            checksum = (checksum >> 16) + (checksum & 0xFFFF);
            checksum = ~checksum;
            icmp_data[2] = (checksum >> 8) & 0xFF;
            icmp_data[3] = checksum & 0xFF;
            // 將數(shù)據(jù)包寫(xiě)入TUN設(shè)備的設(shè)備節(jié)點(diǎn)
            ssize_t num_bytes_sent = write(tun_fd, buffer1, IP_HEADER_LENGTH + 8);

            if (num_bytes_sent < 0) {
            perror("write");
            close(tun_fd);
            return -1;
            }
            printf("Sent %zd bytes to TUN device.\n", num_bytes_sent);
            }
            close(tun_fd);
            return 0;
}

#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <sys/types.h>
#include <linux/if_tun.h>
#include<stdlib.h>
#include<stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define DEST_IP "10.0.0.2"
#define DEST_IP1 "192.168.6.1"


int main()
{

// 創(chuàng)建套接字
            int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
            if (sockfd < 0) {
            perror("Error creating socket");
            //close(tun_fd);
            exit(1);
            }
            sleep(5);
            // 設(shè)置目標(biāo) IP 地址和端口
            printf("------------start-------------------\n");
            struct sockaddr_in dest_addr;
            memset(&dest_addr, 0, sizeof(dest_addr));
            dest_addr.sin_family = AF_INET;
            dest_addr.sin_port = htons(12345);
            inet_pton(AF_INET, DEST_IP, &(dest_addr.sin_addr));

            // 模擬發(fā)送數(shù)據(jù)到 TUN 設(shè)備
            const char* message = "Hello, TUN device!!!!!";

            int sockfd1 = socket(AF_INET, SOCK_DGRAM, 0);
            if (sockfd1 < 0) {
            perror("Error creating socket");
            //close(tun_fd);
            exit(1);
            }
            sleep(5);
            // 設(shè)置目標(biāo) IP 地址和端口
            printf("------------start-------------------\n");
            struct sockaddr_in dest_addr1;
            memset(&dest_addr1, 0, sizeof(dest_addr1));
            dest_addr1.sin_family = AF_INET;
            dest_addr1.sin_port = htons(1234);
            inet_pton(AF_INET, DEST_IP1, &(dest_addr1.sin_addr));

            // 模擬發(fā)送數(shù)據(jù)到 TUN 設(shè)備
            const char* message1 = "tun tunt tunt!!!!!!";

            while(1)
            {
            sendto(sockfd1, message1, strlen(message1), 0, (struct sockaddr*)&dest_addr1, sizeof(dest_addr1));        
               sleep(5);
               sendto(sockfd, message, strlen(message), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr));
            }
            close(sockfd);
            close(sockfd1);
  
}

sudo ./net_device_user1
RTNETLINK answers: File exists
Open tun/tap device: tun0 for reading...

Read 50 bytes from tun/tap device
45 00 00 32 03 FFFFFF9E 40 00 40 11 23 1B 0A 00 00 01 
0A 00 00 02 FFFFFF86 0D 30 39 00 1E 05 27 48 65 6C 6C 
6F 2C 20 54 55 4E 20 64 65 76 69 63 65 21 21 21 
21 21 
Sent 28 bytes to TUN device.
Read 47 bytes from tun/tap device
45 00 00 2F 03 FFFFFF9F 40 00 40 11 23 1D 0A 00 00 01 
0A 00 00 02 FFFFFFC0 3E 04 FFFFFFD2 00 1B FFFFFFF3 FFFFFFDE 74 75 6E 20 
74 75 6E 74 20 74 75 6E 74 21 21 21 21 21 21 
Sent 28 bytes to TUN device.

sudo ./net_device.o
------------start-------------------

sudo tcpdump -i tun0 -w tcpdump_30.pcap
tcpdump: listening on tun0, link-type RAW (Raw IP), capture size 262144 bytes
tcpdump: pcap_loop: The interface went down
16 packets captured
16 packets received by filter
0 packets dropped by kernel

Read 50 bytes from tun/tap device
45 00 00 32 03 FFFFFF9E 40 00 40 11 23 1B 0A 00 00 01 
0A 00 00 02 FFFFFF86 0D 30 39 00 1E 05 27 48 65 6C 6C 
6F 2C 20 54 55 4E 20 64 65 76 69 63 65 21 21 21 
21 21

Read 47 bytes from tun/tap device
45 00 00 2F 03 FFFFFF9F 40 00 40 11 23 1D 0A 00 00 01 
0A 00 00 02 FFFFFFC0 3E 04 FFFFFFD2 00 1B FFFFFFF3 FFFFFFDE 74 75 6E 20 
74 75 6E 74 20 74 75 6E 74 21 21 21 21 21 21