traceroute 通过逐渐变更的TTL值发送UDP包（我见busybox 也有icmp 类型的），然后等待ttl 值变为0的那一跳回复icmp time exceeded 包来测试网络的连通性。首先，traceroute送出一个TTL是1的IP数据包到目的地，当路径上的第一个路由器收到IP数据包时，将TTL减1。此时，TTL变为0，所以将该路由器会将此IP数据包丢掉，并返回一个ICMP time exceeded数据包，当traceroute收到这个消息后，接着继续发生TTL为2的IP数据包给第二个路由器。以此类推，直到IP数据包达到最后一台路由器时，会返回一个ICMP echo reply 或者 地址不可达的数据包。我们通过建立原始套接字来接收返回的icmp 数据包，然后通过解析数据包的字段，析出地址，然后给出连通性的信息。
以下代码存储测试，写完可以跑了就没理了，没考虑过释放内存，关闭套接字等一系列细节，就一测试程序，跑完就结束了。
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#include <stdio.h> #include <stdlib.h> #include <sys/param.h> #include <sys/file.h> #include <sys/ioctl.h> #include <sys/socket.h> #include <sys/time.h> #include <netinet/in_systm.h> #include <netinet/in.h> #include <netinet/ip.h> #include <netinet/ip_icmp.h> #include <netinet/udp.h> #include <arpa/inet.h> #include <ctype.h> #include <errno.h> #include <fcntl.h> #include <malloc.h> #include <memory.h> #include <netdb.h> #include <string.h> #include <unistd.h> //udp packet data payload struct outdata{ u_char seq; u_char ttl; struct timeval tv; }; typedef struct traceInfo{ char host[128]; int min_ttl; int max_ttl; int waittime; int queries; int packsize; int port; }traceInfo_t; typedef struct globalInfo{ struct sockaddr_in haddr; struct sockaddr_in loc_addr; int sendsock; int recvsock; int min_ttl; int max_ttl; int waittime; int queries; int packlen; int port; int ident; int packet[1024]; }globalInfo_t; struct sockaddr_in *outip; struct udphdr *outudp; struct outdata *outdata; globalInfo_t g_info; void tvsub(struct timeval *out, struct timeval *in) { if((out->tv_usec -= in->tv_usec) < 0) { out->tv_sec = out->tv_sec -1; out->tv_usec += 1000000; } out->tv_sec = out->tv_sec - in->tv_sec; } double deltaT(struct timeval *t1p, struct timeval *t2p) { double dt; dt = (double)(t2p->tv_sec - t1p->tv_sec)*1000.0 + (double)(t2p->tv_usec - t1p->tv_usec)/1000.0; return dt; } int getsockaddr_by_host(struct sockaddr_in *sin, char *host) { struct hostent *hent; struct in_addr addr; if(!inet_aton(host,&addr)) { if(!(hent = gethostbyname(host))) { printf("gethostbyname error!\n"); return -1; } addr = *(struct in_addr *)hent->h_addr; } memset(&(sin->sin_addr),0x00,sizeof(sin->sin_addr)); sin->sin_addr = addr; } void init_globalinfo(globalInfo_t *ptr, traceInfo_t *traceInfo) { if(ptr == NULL || traceInfo == NULL) return ; memset(ptr,0,sizeof(*ptr)); ptr->min_ttl = traceInfo->min_ttl; ptr->max_ttl = traceInfo->max_ttl; ptr->waittime = traceInfo->waittime; ptr->queries = traceInfo->queries; ptr->packlen = traceInfo->packsize; ptr->port = traceInfo->port; ptr->ident = (getpid() & 0xffff)|0x8000; //ptr->haddr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in)); //memset(ptr->haddr, 0x00, sizeof(struct sockaddr_in)); getsockaddr_by_host(&(ptr->haddr), traceInfo->host); ptr->haddr.sin_family = AF_INET; ptr->haddr.sin_port = ptr->port; } void send_probe(globalInfo_t *ptr, int seq, int ttl, struct timeval *tp) { int cc; outdata = (struct outdata *)malloc(sizeof(ptr->packlen)); memset(outdata,0,sizeof(ptr->packlen)); ptr->haddr.sin_port = htons(ptr->port+seq); outdata->seq = seq; outdata->ttl = ttl; outdata->tv = *tp; if(setsockopt(ptr->sendsock, IPPROTO_IP, IP_TTL,(char *)&ttl,sizeof(ttl)) < 0) { printf("set ttl error!\n"); return ; } cc = sendto(ptr->sendsock, (char *)outdata, ptr->packlen,0,(struct sockaddr *)&(ptr->haddr),sizeof(ptr->haddr)); if(cc < 0 || cc != ptr->packlen) { printf("send packlen error!\n"); fflush(NULL); return ; } } int wait_for_reply(globalInfo_t *ptr, struct sockaddr_in *from, struct timeval *tp) { fd_set fds; struct timeval now,wait; struct timezone tz; int cc = 0; int sock = ptr->recvsock; int fromlen = sizeof(*from); FD_ZERO(&fds); FD_SET(sock, &fds); wait.tv_sec = tp->tv_sec + ptr->waittime; wait.tv_usec = tp->tv_usec; gettimeofday(&now,&tz); tvsub(&wait,&now); if(select(sock+1, &fds, NULL, NULL,&wait) > 0) cc = recvfrom(sock, (char *)ptr->packet,sizeof(ptr->packet),0,(struct sockaddr *)from, &fromlen); return cc; } int packet_ok(globalInfo_t *ptr,char *buf, int cc, struct sockaddr_in *from,int seq) { struct icmp *icmp; char type, code; int hlen; struct ip *ip; ip = (struct ip *)buf; hlen = ip->ip_hl << 2; if(cc < hlen + ICMP_MINLEN) { printf("packet too short!!\n"); return -1; } cc = cc -hlen; icmp = (struct icmp *)(buf+hlen); type = icmp->icmp_type; code = icmp->icmp_code; if((type == ICMP_TIMXCEED && code == ICMP_TIMXCEED_INTRANS) || type == ICMP_UNREACH || type == ICMP_ECHOREPLY) { struct ip *hip; struct udphdr *hudp; struct icmp *hicmp; hip = &(icmp->icmp_ip); hlen = hip->ip_hl<<2; hudp = (struct udphdr *)((char *)hip + hlen); #if 0 printf("this is init!" ); printf("hlen=%d--->cc=%d\n",hlen,cc); printf("hip->ip_p=%d---->IPPROTO_UDP=%d\n",hip->ip_p,IPPROTO_UDP); printf("hudp->dest=%d---->htons(ptr->port+seq)=%d\n", hudp->dest,htons(ptr->port + seq)); #endif if(hlen +12 <= cc && hip->ip_p == IPPROTO_UDP && /*hudp->source == htons(ptr->ident) &&*/ hudp->dest == htons(ptr->port + seq)) return (type == ICMP_TIMXCEED?-1:code+1); } return 0; } void print(char *buf, int cc, struct sockaddr_in *from ) { struct ip *ip; int hlen; ip = (struct ip *)buf; hlen = ip->ip_hl << 2; cc -= hlen; printf(" %s", inet_ntoa(from->sin_addr)); } int getByDefaultValue(int value,int min,int max) { if( min<value && value < max) return value; else if(value > max) return max; else if(value < min) return min; else return min; } void trace(traceInfo_t *traceInfo) { int on = 1; int ttl,probe; struct sockaddr_in *from; int seq = 0; int code; int i=0; int minipacket,packlen; if(traceInfo == NULL) return ; init_globalinfo(&g_info,traceInfo); minipacket = sizeof(*outip) + sizeof(outdata); packlen = minipacket + sizeof(*outudp); g_info.packlen = getByDefaultValue(g_info.packlen,minipacket,32*1024); from = malloc(sizeof(struct sockaddr_in)); memset(from,0x00,sizeof(struct sockaddr_in)); //setlinebuf(stdout); #if 0 outip = (struct ip *)malloc((unsigned)packlen); if(outip == NULL) { printf("outip is null!\n"); return ; } memset((char *)outip,0,packlen); outip->ip_v = IPVERSION; outip->ip_len = packlen; outip->ip_off = 0; outp #endif if((g_info.sendsock=socket(AF_INET, SOCK_DGRAM, 0)) < 0) { printf("create sendsock error!\n"); return ; } if((g_info.recvsock = socket(AF_INET,SOCK_RAW,IPPROTO_ICMP)) < 0) { printf("create recvsock error!\n"); return ; } #if 0 if(setsockopt(g_info.sendsock, IPPROTO_IP, IP_HDRINCL,(char *)&on,sizeof(on)) < 0) { printf("setopt error!\n"); return ; } #endif printf("traceroute to %s (%s)\n",traceInfo->host,inet_ntoa(g_info.haddr.sin_addr)); fflush(NULL); for(ttl=g_info.min_ttl; ttl < g_info.max_ttl; ++ttl) { u_int32_t lastaddr = 0; int gotlastaddr = 0; int got_there = 0; int unreachable = 0; int sentfirst = 0; printf("%2d\t",ttl); for(probe = 0; probe<g_info.queries; ++probe) { int cc; struct timeval t1,t2; struct timezone tz; struct ip *ip; gettimeofday(&t1,&tz); send_probe(&g_info,++seq,ttl,&t1); ++sentfirst; while((cc = wait_for_reply(&g_info,from,&t1)) != 0) { gettimeofday(&t2,&tz); i = packet_ok(&g_info,(char *)g_info.packet,cc,from,seq); if(i == 0) continue; if(!gotlastaddr || from->sin_addr.s_addr != lastaddr) { print((char *)g_info.packet,cc,from); lastaddr = from->sin_addr.s_addr; ++gotlastaddr; } printf(" %.3f ms",deltaT(&t1,&t2)); if(i == -1) break; code = i -1; switch(code) { case ICMP_UNREACH_PORT: ++got_there; break; case ICMP_UNREACH_NET: ++unreachable; printf(" !N"); break; case ICMP_UNREACH_HOST: ++unreachable; printf(" !H"); break; case ICMP_UNREACH_PROTOCOL: ++got_there; printf(" !P"); default: ++unreachable; printf("!<%d>",code); break; } break; } if(cc == 0) printf(" *"); fflush(NULL); } printf("\n"); if(got_there || unreachable > 0 && (unreachable >= g_info.queries -1)) { break; } } } int main(void) { traceInfo_t traceInfo; strcpy(traceInfo.host,"www.baidu.com"); traceInfo.min_ttl = 1; traceInfo.max_ttl = 30; traceInfo.waittime = 5; traceInfo.queries = 3; traceInfo.packsize = 50; traceInfo.port = 32758 + 666; trace(&traceInfo); return 0; } |