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是否有人可以帮助我锻炼为什么我的ICMP序列号不会在每个请求中递增，当它被用作ping程序时，它会增加每个ping的序列号。 也没有人有任何想法为什么我的往返时间显示为负数？当这是一个ping程序时，这也工作得很好。为什么我的ICMP序列号不递增？ （C Socket编程）
请承担所有的代码'作品'，我已经删除了一些更容易阅读。
void
respond (int signum) {
struct sockaddr_storage peer_addr;
socklen_t peer_addrlen;
struct sockaddr_in addr;
struct sockaddr_in dstaddr;
struct iphdr * ip;
struct icmphdr * icmp;
struct timeval * sent;
int skt;
int sequence = 0;
long int length;
fd_set rdfds;
int ready;
int rtt;
char buff [BUF_SIZE];
/* Create and check Socket Number */
skt = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
int ttl = 0;
setsockopt(skt, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl)) < 0;
/* Check Socket */
if (skt < 0) {
perror ("socket()");
exit (1);
}
/* Set IP Addresses */
addr.sin_family = AF_INET;
addr.sin_port = 0;
addr.sin_addr.s_addr = INADDR_ANY;
/* Check Socket Bind */
if (bind (skt, (struct sockaddr *)&addr, sizeof(struct sockaddr_in))) {
perror ("Can't bind socket");
exit (1);
}
/* START SEND LOOP*/
int i;
for (i = 0; i < 7; i++){
ttl+=1;
setsockopt(skt, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
/* IP Buffer */
ip = (struct iphdr *)buff;
peer_addrlen = (socklen_t) sizeof (struct sockaddr_storage);
memset (&dstaddr, 0, sizeof(struct sockaddr_in));
dstaddr.sin_addr.s_addr = inet_addr(HOSTADDR);
dstaddr.sin_family = AF_INET;
/* ICMP Buffer */
memset (buff, 0, sizeof(buff));
icmp = (struct icmphdr *) buff;
icmp->type = ECHO_REQ;
icmp->id = htons(getpid() & 0xffff);
icmp->seqNum = htons(sequence++);
/* Check Send Time */
if (gettimeofday ((struct timeval *)icmp->data, NULL)) {
perror ("Can't establish send time");
exit (1);
}
/*Calculating packet size*/
length = sizeof(struct icmphdr) + sizeof(struct timeval);
icmp->checksum = ~(sum (0, buff, length));
/* Packet too small, ERROR
SEND Request */
if (sendto (skt, buff, length, 0,
(struct sockaddr *) &dstaddr, sizeof(struct sockaddr_in)) <= 0) {
perror ("sendto()");
exit (1);
}
/* Define File Descriptor */
timeout.tv_sec = 1;
timeout.tv_usec = 1;
FD_ZERO(&rdfds);
FD_SET (skt, &rdfds);
/* Select Data from File Descriptor */
ready = select (skt + 1, &rdfds, NULL, NULL, &timeout);
if (ready < 0) {
perror ("Select()");
exit (1);
}
/* Recieve Reply */
memset (buff, 0, sizeof(buff));
if (recvfrom (skt, buff, sizeof(buff), 0,
(struct sockaddr *) &peer_addr, &peer_addrlen) <= 0) exit (1);
/* Check Time Stamp */
if (gettimeofday (&end, NULL)) { // Timestamp reception
perror ("Can't establish time of receipt");
exit (1);
}
/* Check IP Protocol */
if (ip->version != 4 ||
sum (0, buff, sizeof(struct iphdr)) != 0xffff ||
ip->protocol != ICMP)
exit(1);
/* Get IP Payload legth and ICMP Address*/
length = ntohs(ip->length) - ip->hdrlen * 4; // Length of IP payload
icmp = (struct icmphdr *)((uint32_t *)ip + ip->hdrlen); // Find ICMP hdr
/* Check ICMP response type*/
if (icmp->type == 11){
printf("");
}
/* if (icmp->type != ECHO_REPL || sum (0, icmp, length) != 0xffff) {
fprintf (stderr, "Received %s\n", messages[icmp->type]);
//exit (1);
} */
/* Find the difference between sent and end times in 10s of ms */
sent = (struct timeval *)icmp->data;
if ((rtt = (end.tv_usec - sent->tv_usec)/10) < 0)
rtt += 10000; // We've cycled to a new second
rtt += (end.tv_sec - sent->tv_sec) * 10000; // Add any seconds
/* PRINT ICMP REPLY*/
printf ("%ld bytes from %s: icmp_req=%d ttl=%d time= %0.1f ms\n",
length,
iptos(ntohl(ip->srcip)),
ntohs(icmp->seqNum),
ip->ttl,
((float)rtt)/10);
} /*END SEND LOOP
/* 3 Second Probe */
alarm (5);
}
同样的问题仍然存在，它在这个程序的ping版本中工作 –
对于所有7次迭代它是否保持0？您也可以使用您添加的任何修补程序更新代码。 – Eric
哦，我看到发生了什么。您将在循环的每次迭代过程中重新分配“icmp”的值。首先，它是为你的传出数据包，然后重新分配对该变量的响应。 发生了什么是您将序列设置为3，但TTL过期正在被发送回来，将序列重置为0.当您和目标之间存在一些随机路由器时，您无法预期该序列是预期的正在拦截并回复带有错误消息的请求。 – Eric