Question

我正在为学校写一个traceroute程序。它适用于某些网站（如www.google.fr），程序无法到达目的地：它在第9跳后停止。

Domain: www.google.fr
Address: 173.194.40.159

 1  172.29.255.253  172.29.255.253
 2  130.79.209.197  routeur-espla-rc1-130-79-209-197.u-strasbg.fr
 3  * * * 
 4  193.51.189.85   te1-2-nancy-rtr-021.noc.renater.fr
 5  193.51.189.161  te0-0-0-2-paris1-rtr-001.noc.renater.fr
 6  193.51.189.6    te0-0-0-0-paris2-rtr-001.noc.renater.fr
 7  * * * 
 8  193.51.182.197  193.51.182.197
 9  72.14.238.228   72.14.238.228
 10 * * * 
 11 * * * 
 ...
 30 * * *

真正的traceroute没有问题：

traceroute to www.google.fr (173.194.40.223), 30 hops max, 60 byte packets
 1  172.29.255.253 (172.29.255.253)  3.575 ms  3.588 ms  4.119 ms
 2  routeur-espla-rc1-130-79-209-197.u-strasbg.fr (130.79.209.197)  4.321 ms  4.273 ms  5.032 ms
 3  * * *
 4  te1-2-nancy-rtr-021.noc.renater.fr (193.51.189.85)  11.216 ms  11.662 ms  12.960 ms
 5  te0-0-0-2-paris1-rtr-001.noc.renater.fr (193.51.189.161)  14.655 ms  14.637 ms  14.615 ms
 6  te0-0-0-0-paris2-rtr-001.noc.renater.fr (193.51.189.6)  14.588 ms  213.011 ms  18.148 ms
 7  * * *
 8  193.51.182.197 (193.51.182.197)  11.062 ms  11.084 ms  11.243 ms
 9  72.14.238.228 (72.14.238.228)  12.217 ms  12.765 ms  17.578 ms
10  209.85.243.51 (209.85.243.51)  13.511 ms  17.515 ms  17.493 ms
11  par10s12-in-f31.1e100.net (173.194.40.223)  13.183 ms  14.091 ms  14.054 ms

以下是循环和更改TTL值的函数的代码：

void LoopUDP(int rcvt, int sndt, int ttl_t[3],
             struct sockaddr_in server, struct sockaddr_in my_addr)
{
    struct timeval r_timeout = { rcvt, 0 };
    struct timeval s_timeout = { sndt, 0 };

    Socket send_socket, receive_socket;
    socklen_t addrlen = sizeof (struct sockaddr_in);

    struct sockaddr_in recept = { 0 };

    char recvbuf[MAX_PACKET];
    char *host = NULL, *rsaddr = NULL;

    char dest[MAX_ADDRESS];
    strcpy(dest, inet_ntoa(server.sin_addr));

    int reach_dest = 0;

    int tent, tentative = 3;

    int ttl, min_ttl = ttl_t[0], max_ttl = ttl_t[1], hops = ttl_t[2];

    for (ttl = min_ttl; ttl <= max_ttl; ttl += hops)
    {
        send_socket    = OpenDgramSocket('U');
        receive_socket = OpenRawSocket('I');

        if (bind(receive_socket, (struct sockaddr*)&my_addr, addrlen) == -1)
        {
            perror("bind receive socket");
            exit(-1);
        }

        if ( ! SetTTL(send_socket, ttl))                 exit(-1);
        if ( ! SetSNDTimeOut(send_socket, s_timeout))    exit(-1);
        if ( ! SetRCVTimeOut(receive_socket, r_timeout)) exit(-1);

        if (sendto(send_socket, "hello", 4, 0, (struct sockaddr*) &server, addrlen) == -1)
        {
            perror("sendto()");
        }
        else
        {
            printf(" %-2d ", ttl);
            for (tent = 0; tent < tentative; tent++)
            {
                if (recvfrom(receive_socket, recvbuf, MAX_PACKET, 0, (struct sockaddr*)&recept, &addrlen) == -1)
                {
                    printf("* ");
                }
                else
                {
                    rsaddr = inet_ntoa(recept.sin_addr);
                    host = GetHostNameFromIP(rsaddr);
                    printf("%-15s %s", rsaddr, host);
                    if (strcmp(dest, rsaddr)==0)
                    {
                        reach_dest = 1;
                    }
                    break;
                }
            }
            printf("\n");
        }

        close(send_socket);
        close(receive_socket);

        if (reach_dest) return;
    }
}

你知道为什么它没有到达目的地吗？国旗问题？

我的traceroute无法到达目的地

0 个答案: