TraceRoute实现

网络课上老师布置了第二个作业，写一个TraceRoute的程序。

Traceroute的工作原理：
Traceroute程序的设计是利用ICMP及IP header的TTL（Time To Live）栏位（field）。首先，traceroute送出一个TTL是1的IP datagram（其实，每次送出的为3个40字节的包，包括源地址，目的地址和包发出的时间标签）到目的地，当路径上的第一个路由器（router）收到这个datagram时，它将TTL减1。此时，TTL变为0了，所以该路由器会将此datagram丢掉，并送回一个ICMP time exceeded消息（包括发IP包的源地址，IP包的所有内容及路由器的IP地址），traceroute 收到这个消息后，便知道这个路由器存在于这个路径上，接着traceroute 再送出另一个TTL是2 的datagram，发现第2 个路由器...... traceroute 每次将送出的datagram的TTL 加1来发现另一个路由器，这个重复的动作一直持续到某个datagram 抵达目的地。当datagram到达目的地后，该主机并不会送回ICMP time exceeded消息，因为它已是目的地了，那么traceroute如何得知目的地到达了呢？
Traceroute在送出UDP datagrams到目的地时，它所选择送达的port number 是一个一般应用程序都不会用的号码（30000 以上），所以当此UDP datagram 到达目的地后该主机会送回一个「ICMP port unreachable」的消息，而当traceroute 收到这个消息时，便知道目的地已经到达了。所以traceroute 在Server端也是没有所谓的Daemon 程式。
Traceroute提取发 ICMP TTL到期消息设备的IP地址并作域名解析。每次，Traceroute都打印出一系列数据,包括所经过的路由设备的域名及 IP地址,三个包每次来回所花时间。
Traceroute 有一个固定的时间等待响应(ICMP TTL到期消息)。如果这个时间过了，它将打印出一系列的*号表明：在这个路径上，这个设备不能在给定的时间内发出ICMP TTL到期消息的响应。然后，Traceroute给TTL记数器加1，继续进行。

TraceRoute.h如下：

#ifndef _ITRACERT_H_
#define _ITRACERT_H_
#pragma pack(1)
//IP数据报头
typedef struct
{unsigned char hdr_len :4;  // length of the headerunsigned char version :4;  // version of IPunsigned char tos;   // type of serviceunsigned short total_len;  // total length of the packetunsigned short identifier;  // unique identifierunsigned short frag_and_flags; // flagsunsigned char ttl;   // time to liveunsigned char protocol;  // protocol (TCP, UDP etc)unsigned short checksum;  // IP checksumunsigned long sourceIP;  // source IP addressunsigned long destIP;   // destination IP address
} IP_HEADER;
//ICMP数据报头
typedef struct
{BYTE type;  //8位类型BYTE code;  //8位代码USHORT cksum;  //16位校验和USHORT id;   //16位标识符USHORT seq;  //16位序列号
} ICMP_HEADER;
//解码结果
typedef struct
{USHORT usSeqNo;   //包序列号DWORD dwRoundTripTime; //往返时间in_addr dwIPaddr;  //对端IP地址
} DECODE_RESULT;
#pragma pack()
//ICMP类型字段
const BYTE ICMP_ECHO_REQUEST = 8; //请求回显
const BYTE ICMP_ECHO_REPLY  = 0; //回显应答
const BYTE ICMP_TIMEOUT   = 11; //传输超时
const DWORD DEF_ICMP_TIMEOUT = 3000; //默认超时时间，单位ms
const int DEF_ICMP_DATA_SIZE = 32; //默认ICMP数据部分长度
const int MAX_ICMP_PACKET_SIZE = 1024; //最大ICMP数据报的大小
const int DEF_MAX_HOP = 30;    //最大跳站数
USHORT GenerateChecksum(USHORT* pBuf, int iSize);
BOOL DecodeIcmpResponse(char* pBuf, int iPacketSize, DECODE_RESULT& stDecodeResult);
#endif // _ITRACERT_H_

TraceRoute.cpp如下：

#include <iostream>
#include <iomanip>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include "TraceRoute.h"
#pragma comment(lib,"ws2_32")
using namespace std;
int main(int argc, char* argv[])
{//检查命令行参数if (argc != 2){cerr << "\nUsage: itracert ip_or_hostname\n";return -1;}//初始化winsock2环境WSADATA wsa;if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0){cerr << "\nFailed to initialize the WinSock2 DLL\n"<< "error code: " << WSAGetLastError() << endl;return -1;}//将命令行参数转换为IP地址u_long ulDestIP = inet_addr(argv[1]);if (ulDestIP == INADDR_NONE){//转换不成功时按域名解析hostent* pHostent = gethostbyname(argv[1]);if (pHostent){ulDestIP = (*(in_addr*)pHostent->h_addr).s_addr;//输出屏幕信息cout << "\nTracing route to " << argv[1] << " [" << inet_ntoa(*(in_addr*)(&ulDestIP)) << "]"<< " with a maximum of " << DEF_MAX_HOP << " hops.\n" << endl;}else //解析主机名失败{cerr << "\nCould not resolve the host name " << argv[1] << '\n'<< "error code: " << WSAGetLastError() << endl;WSACleanup();return -1;}}else{//输出屏幕信息cout << "\nTracing route to " << argv[1] << " with a maximum of " << DEF_MAX_HOP << " hops.\n" << endl;}//填充目的Socket地址sockaddr_in destSockAddr;ZeroMemory(&destSockAddr, sizeof(sockaddr_in));destSockAddr.sin_family = AF_INET;destSockAddr.sin_addr.s_addr = ulDestIP;//使用ICMP协议创建Raw SocketSOCKET sockRaw = WSASocket(AF_INET, SOCK_RAW, IPPROTO_ICMP, NULL, 0, WSA_FLAG_OVERLAPPED);if (sockRaw == INVALID_SOCKET){cerr << "\nFailed to create a raw socket\n"<< "error code: " << WSAGetLastError() << endl;WSACleanup();return -1;}//设置端口属性int iTimeout = DEF_ICMP_TIMEOUT;if (setsockopt(sockRaw, SOL_SOCKET, SO_RCVTIMEO, (char*)&iTimeout, sizeof(iTimeout)) == SOCKET_ERROR){cerr << "\nFailed to set recv timeout\n"<< "error code: " << WSAGetLastError() << endl;closesocket(sockRaw);WSACleanup();return -1;}//创建ICMP包发送缓冲区和接收缓冲区char IcmpSendBuf[sizeof(ICMP_HEADER)+DEF_ICMP_DATA_SIZE];memset(IcmpSendBuf, 0, sizeof(IcmpSendBuf));char IcmpRecvBuf[MAX_ICMP_PACKET_SIZE];memset(IcmpRecvBuf, 0, sizeof(IcmpRecvBuf));//填充待发送的ICMP包ICMP_HEADER* pIcmpHeader = (ICMP_HEADER*)IcmpSendBuf;pIcmpHeader->type = ICMP_ECHO_REQUEST;pIcmpHeader->code = 0;pIcmpHeader->id = (USHORT)GetCurrentProcessId();memset(IcmpSendBuf+sizeof(ICMP_HEADER), 'E', DEF_ICMP_DATA_SIZE);//开始探测路由DECODE_RESULT stDecodeResult;BOOL bReachDestHost = FALSE;USHORT usSeqNo = 0;int iTTL = 1;int iMaxHop = DEF_MAX_HOP;while (!bReachDestHost && iMaxHop--){//设置IP数据报头的ttl字段setsockopt(sockRaw, IPPROTO_IP, IP_TTL, (char*)&iTTL, sizeof(iTTL));//输出当前跳站数作为路由信息序号cout << setw(3) << iTTL << flush;//填充ICMP数据报剩余字段((ICMP_HEADER*)IcmpSendBuf)->cksum = 0;((ICMP_HEADER*)IcmpSendBuf)->seq = htons(usSeqNo++);((ICMP_HEADER*)IcmpSendBuf)->cksum = GenerateChecksum((USHORT*)IcmpSendBuf, sizeof(ICMP_HEADER)+DEF_ICMP_DATA_SIZE);//记录序列号和当前时间stDecodeResult.usSeqNo = ((ICMP_HEADER*)IcmpSendBuf)->seq;stDecodeResult.dwRoundTripTime = GetTickCount();//发送ICMP的EchoRequest数据报if (sendto(sockRaw, IcmpSendBuf, sizeof(IcmpSendBuf), 0, (sockaddr*)&destSockAddr, sizeof(destSockAddr)) == SOCKET_ERROR){//如果目的主机不可达则直接退出if (WSAGetLastError() == WSAEHOSTUNREACH)cout << '\t'<< "Destination host unreachable.\n"<< "\nTrace complete.\n" << endl;closesocket(sockRaw);WSACleanup();return 0;}//接收ICMP的EchoReply数据报//因为收到的可能并非程序所期待的数据报，所以需要循环接收直到收到所要数据或超时sockaddr_in from;int iFromLen = sizeof(from);int iReadDataLen;while (1){//等待数据到达iReadDataLen = recvfrom(sockRaw, IcmpRecvBuf, MAX_ICMP_PACKET_SIZE, 0, (sockaddr*)&from, &iFromLen);if (iReadDataLen != SOCKET_ERROR) //有数据包到达{//解码得到的数据包，如果解码正确则跳出接收循环发送下一个EchoRequest包if (DecodeIcmpResponse(IcmpRecvBuf, iReadDataLen, stDecodeResult)){if (stDecodeResult.dwIPaddr.s_addr == destSockAddr.sin_addr.s_addr)bReachDestHost = TRUE;cout << '\t' << inet_ntoa(stDecodeResult.dwIPaddr) << endl;break;}}else if (WSAGetLastError() == WSAETIMEDOUT) //接收超时，打印星号{cout << setw(9) << '*' << '\t' << "Request timed out." << endl;break;}else{cerr << "\nFailed to call recvfrom\n"<< "error code: " << WSAGetLastError() << endl;closesocket(sockRaw);WSACleanup();return -1;}}//TTL值加1iTTL++;}//输出屏幕信息cout << "\nTrace complete.\n" << endl;closesocket(sockRaw);WSACleanup();return 0;
}
//产生网际校验和
USHORT GenerateChecksum(USHORT* pBuf, int iSize) 
{unsigned long cksum = 0;while (iSize>1) {cksum += *pBuf++;iSize -= sizeof(USHORT);}if (iSize) cksum += *(UCHAR*)pBuf;cksum = (cksum >> 16) + (cksum & 0xffff);cksum += (cksum >> 16);return (USHORT)(~cksum);
}
//解码得到的数据报
BOOL DecodeIcmpResponse(char* pBuf, int iPacketSize, DECODE_RESULT& stDecodeResult)
{//检查数据报大小的合法性IP_HEADER* pIpHdr = (IP_HEADER*)pBuf;int iIpHdrLen = pIpHdr->hdr_len * 4;if (iPacketSize < (int)(iIpHdrLen+sizeof(ICMP_HEADER)))return FALSE;//按照ICMP包类型检查id字段和序列号以确定是否是程序应接收的Icmp包ICMP_HEADER* pIcmpHdr = (ICMP_HEADER*)(pBuf+iIpHdrLen);USHORT usID, usSquNo;if (pIcmpHdr->type == ICMP_ECHO_REPLY){usID = pIcmpHdr->id;usSquNo = pIcmpHdr->seq;}else if(pIcmpHdr->type == ICMP_TIMEOUT){char* pInnerIpHdr = pBuf+iIpHdrLen+sizeof(ICMP_HEADER);  //载荷中的IP头int iInnerIPHdrLen = ((IP_HEADER*)pInnerIpHdr)->hdr_len * 4;//载荷中的IP头长ICMP_HEADER* pInnerIcmpHdr = (ICMP_HEADER*)(pInnerIpHdr+iInnerIPHdrLen);//载荷中的ICMP头usID = pInnerIcmpHdr->id;usSquNo = pInnerIcmpHdr->seq;}elsereturn FALSE;if (usID != (USHORT)GetCurrentProcessId() || usSquNo !=stDecodeResult.usSeqNo) return FALSE;//处理正确收到的ICMP数据报if (pIcmpHdr->type == ICMP_ECHO_REPLY ||pIcmpHdr->type == ICMP_TIMEOUT){//返回解码结果stDecodeResult.dwIPaddr.s_addr = pIpHdr->sourceIP;stDecodeResult.dwRoundTripTime = GetTickCount()-stDecodeResult.dwRoundTripTime;//打印屏幕信息if (stDecodeResult.dwRoundTripTime)cout << setw(6) << stDecodeResult.dwRoundTripTime << " ms" << flush;elsecout << setw(6) << "<1" << " ms" << flush;return TRUE;}return FALSE;
}

运行截图1（查看本机到华科网络实验室的路由信息）如下：