struct route_t {

        struct in_addr dest_addr;
        struct in_addr gateway;
        struct in_addr mask;
        char interface[iface_len]; // #define IFNAMSIZ 8
};


// HWADDR=, 其中 以AA:BB:CC:DD:EE:FF形式的以太网设备的硬件地址
struct device_t // 记录mac地址
{

        char interface[iface_len];
        unsigned char hwaddr [ETH_ALEN]; // define ETH_ALEN 6 {AA : BB : CC : DD : EE :FF }
};

struct arp_t  // 记录主机ip地址和mac地址的对应关系
{

    struct in_addr ip_addr;
    unsigned char hwaddr[ETH_ALEN];
};

int sockfd = socket(AF_PACKET,SOCK_RAW,htons(ETH_P_ALL));

        struct sockaddr_ll addr;
        socklen_t addr_len = sizeof(addr);
        int rev_result = recvfrom(sockfd,buffer,BUF_LEN,0,(struct sockaddr *) &addr,& addr_len);

       // 获得下一跳的IP地址 ,遍历arp_table
        struct in_addr next_addr;
        next_addr.s_addr = ip_head->daddr;
        //
        //next_addr = 
        int arp_i;
        for( arp_i = 0; arp_i < arp_tbl_len;arp_i++)
        {
            if(arp_tbl[arp_i].ip_addr.s_addr == next_addr.s_addr)
                break;

        }
        if(arp_i == 2)
            arp_i = 1;
       	 printf("arp_i : %d\n",arp_i);
      //  struct in_addr temp_addr
     //   next_addr = route_tbl[index].gateway;
        //修改报头，准备重新发送数据
        memcpy(eth_head->h_source, eth_head->h_dest,ETH_ALEN);
        memcpy(eth_head->h_dest,arp_tbl[arp_i].hwaddr,ETH_ALEN);

        int sockf_inter = socket(AF_PACKET,SOCK_DGRAM,htons(ETH_P_IP));
        struct ifreq req;
        memset(&req,0,sizeof(req));
        strncpy(req.ifr_name,route_tbl[index].interface,IFNAMSIZ - 1);
        ioctl(sockf_inter,SIOCGIFINDEX,&req);
        int if_index = req.ifr_ifindex;
        printf("index name : %d \n",if_index);
        //重新发送数据
        int sock2send = socket(AF_PACKET, SOCK_DGRAM,htons(ETH_P_IP));
        struct sockaddr_ll dest2addr = {
            .sll_family = AF_PACKET,
            .sll_protocol = htons(ETH_P_IP),
            .sll_halen = ETH_ALEN,
            .sll_ifindex = if_index,
        };
        ioctl(sockf_inter,SIOCGIFHWADDR,&req);
        memcpy(dest2addr.sll_addr,arp_tbl[arp_i].hwaddr,ETH_ALEN);
        int result = sendto(sockfd,buffer,rev_result,0,(struct sockaddr *)&dest2addr,sizeof(dest2addr));

sockfd = Socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

    struct ifreq ifreq_i;
    memset(&ifreq_i,0,sizeof(ifreq_i));
    //giving name of Interface
    strncpy(ifreq_i.ifr_name, IFACE_NAME, IFNAMSIZ-1); 
    //getting Interface Index 
    Ioctl(sockfd, SIOCGIFINDEX, &ifreq_i); 
    sadr_ll.sll_ifindex = ifreq_i.ifr_ifindex; // index of interface

    sadr_ll.sll_halen = ETH_ALEN;
    sadr_ll.sll_family = AF_PACKET;
    memcpy(sadr_ll.sll_addr, NEXT_HWADDR, ETH_ALEN);

    struct ethhdr *eth_head = (struct ethhdr *)(send_buffer);
    memcpy(eth_head->h_source,PC_HWADDR,ETH_ALEN);
    memcpy(eth_head->h_dest,NEXT_HWADDR,ETH_ALEN);
    eth_head->h_proto = htons(ETH_P_IP);

    struct iphdr *ip_head = (struct iphdr *)(send_buffer + sizeof(ethhdr));
    ip_head->version = 4;
    ip_head->ihl = 5;
    ip_head->ttl = 64;
    ip_head->protocol = 1;	// ICMP
    ip_head->saddr = inet_addr(LOCAL_IP);
    ip_head->daddr = inet_addr(DST_IP);
    ip_head->tot_len = htons(sizeof(struct iphdr) + ICMP_PACKET_LEN);
    ip_head->check = cal_chksum((void *)ip_head, sizeof(struct iphdr));

    struct icmphdr *icmp_head = (struct icmphdr *)(send_buffer + sizeof(ethhdr) + sizeof(iphdr));

    icmp_head->type  = ICMP_ECHO; //8 – Echo Request
    icmp_head->code  = 0;
    // icmp_hdr->checksum = 0;
    //icmp_head->un.echo.id = htons(getpid());
    icmp_head->icmp_id = uid;
    icmp_head->un.echo.sequence = htons(sequence);

    gettimeofday((struct timeval *)((char *)icmp_head+sizeof(struct icmphdr)),NULL);
    icmp_head->checksum =cal_chksum((unsigned short*)icmp_head, ICMP_PACKET_LEN);

    /* Send Ethernet frame */
    int total_len = sizeof(struct ethhdr) + sizeof(struct iphdr) + ICMP_PACKET_LEN;

    int send_end = sendto(sockfd, sendbuf, total_len, 0,
    (const struct sockaddr*)&sadr_ll,sizeof(struct sockaddr_ll)

    sock_r = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));

    int  result = recvfrom(sock_r,buffer,BUFFSIZ,0, NULL, NULL);

    struct ethhdr *eth = (struct ethhdr *)(buffer);
    if (strncmp((char *)eth->h_source, (char *)LOCAL_HWADDR, ETH_ALEN) &&
    strncmp((char *)eth->h_source, (char *)BROADCAST_HWADDR, ETH_ALEN))
    continue;
    printf("Ethernet header checked\n");


    // Extracting the IP header
    struct iphdr *ip = (struct iphdr*)(buffer + sizeof(struct ethhdr));
    struct in_addr local_in_addr, dst_in_addr;
    inet_aton(LOCAL_IP, &local_in_addr);
    dst_in_addr.s_addr = ip->daddr;
    if (local_in_addr.s_addr != dst_in_addr.s_addr || ip->protocol != 1)
    continue;
    printf("IP header checked\n");

    // Extracting the ICMP header
    struct icmphdr *icmp_hdr = 
    (struct icmphdr *)(buffer + sizeof(struct ethhdr) + sizeof(struct iphdr));
    if (icmp_hdr->type  != ICMP_ECHO)
        continue;
    printf("ICMP header checked\n");

​    memcpy(eth->h_source, eth->h_dest, ETH_ALEN);
    memcpy(eth->h_dest, NEXT_HOP_HWADDR, ETH_ALEN);

​    // Change the source and destination IP address
    ip->daddr = ip->saddr;
    ip->saddr = inet_addr(LOCAL_IP);

​    ip->check = 0;
    ip->check = cal_chksum((unsigned short *)ip, sizeof(struct iphdr));

​    // Change ICMP header
    icmp_hdr->type = ICMP_ECHOREPLY;
    icmp_hdr->checksum = 0;
    icmp_hdr->checksum = cal_chksum((unsigned short *)icmp_hdr, 
    sizeof(struct icmphdr) + sizeof(struct timeval));

int result_send = sendto(sock_r, buffer, buflen, 0,
    (const struct sockaddr*)&sadr_ll,sizeof(struct sockad

    const char *arp_ip2 = "192.168.2.2";
    const char arp_hw2[ETH_ALEN] = {0x00,0x0c,0x29,0x3f,0x3b,0x15};

    strncpy(arp_tbl[0].hwaddr,arp_hw1,ETH_ALEN);
    strncpy(arp_tbl[1].hwaddr,arp_hw2,ETH_ALEN);