路由跟踪技术

用来确定路由器的IP地址，也就是在网络上到达特定主机所经过的计算机。

程序需要两个套接字：

1 一个用于接收ICMP封包的原始套接字sRaw

2 用于发送TTL不断增加UDP封包的套接字sSend。

实现代码如下：

void main()
{
    char *szDestIp = "10.16.115.178"; // 210.181.18.12910.16.115.25 61.55.66.30

    char recvBuf[1024] = { 0 };

    // 创建用于接收ICMP封包的原始套节字，绑定到本地端口
    SOCKET sRaw = ::socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    sockaddr_in in;
    in.sin_family = AF_INET;
    in.sin_port = 0;
    in.sin_addr.S_un.S_addr = INADDR_ANY;
    if(::bind(sRaw, (sockaddr*)&in, sizeof(in)) == SOCKET_ERROR)
    {
        printf(" bind() failed \n");
        return;
    }

    SetTimeout(sRaw, 5*1000);

    // 创建用于发送UDP封包的套节字
    SOCKET sSend = ::socket(AF_INET, SOCK_DGRAM, 0);    
    
    SOCKADDR_IN destAddr;
    destAddr.sin_family = AF_INET;
    destAddr.sin_port = ::htons(22);
    destAddr.sin_addr.S_un.S_addr = ::inet_addr(szDestIp);


    int nTTL = 1;
    int nRet;
    ICMP_HDR *pICMPHdr;
    int nTick;    
    SOCKADDR_IN recvAddr;
    do
    {
        // 设置UDP封包的TTL值
        SetTTL(sSend, nTTL);
        nTick = ::GetTickCount();

        // 发送这个UDP封包
        nRet = ::sendto(sSend, "hello", 5, 0, (sockaddr*)&destAddr, sizeof(destAddr));
        if(nRet == SOCKET_ERROR)
        {
            printf(" sendto() failed \n");
            break;
        }


        // 等待接收路由器返回的ICMP报文
        int nLen = sizeof(recvAddr);
        nRet = ::recvfrom(sRaw, recvBuf, 1024, 0, (sockaddr*)&recvAddr, &nLen);
        if(nRet == SOCKET_ERROR)
        {
            if(::WSAGetLastError() == WSAETIMEDOUT)
            {
                printf(" time out \n");
                break;
            }
            else
            {
                printf(" recvfrom() failed \n");
                break;
            }
        }

        // 解析接收到的ICMP数据
        pICMPHdr = (ICMP_HDR*)&recvBuf[20]; // sizeof(IPHeader)

        if(pICMPHdr->icmp_type != 11 && pICMPHdr->icmp_type != 3 && pICMPHdr->icmp_code != 3)
        {
            printf(" Unexpected Type: %d , code: %d \n",
                pICMPHdr->icmp_type, pICMPHdr->icmp_code);
        }
        else
        {
            char *szIP = ::inet_ntoa(recvAddr.sin_addr);
            
            printf(" 第%d个路由器，IP地址：%s \n", nTTL, szIP);
            printf("      用时：%d毫秒 \n", ::GetTickCount() - nTick);
        }
        
        if(destAddr.sin_addr.S_un.S_addr == recvAddr.sin_addr.S_un.S_addr)
        {    
            printf("目标可达 \n");
            break;
        }

        printf("//------------------------------------// \n");

    }while(nTTL++ < 20);

    ::closesocket(sRaw);
    ::closesocket(sSend);
}