struct ip
{
#if __BYTE_ORDER == __LITTLE_ENDIAN
unsigned int ip_hl:4 /* header length */
unsigned int ip_v:4 /* version */
#endif
#if __BYTE_ORDER == __BIG_ENDIAN
unsigned int ip_v:4 /* version */
unsigned int ip_hl:4 /* header length */
#endif
u_int8_t ip_tos /* type of service */
u_short ip_len /* total length */
u_short ip_id /* identification */
u_short ip_off /* fragment offset field */
#define IP_RF 0x8000 /* reserved fragment flag */
#define IP_DF 0x4000 /* dont fragment flag */
#define IP_MF 0x2000 /* more fragments flag */
#define IP_OFFMASK 0x1fff /* mask for fragmenting bits */
u_int8_t ip_ttl /* time to live */
u_int8_t ip_p /* protocol */
u_short ip_sum /* checksum */
struct in_addr ip_src, ip_dst /* source and dest address */
}
如果你仅仅是想改变某个IP包里面的ttl值，你需要自己创建这个ip结构。如果你是想在创建socket的时候改ttl值，用setsockopt函数
1.首先将标志位设为Non-blocking模式，准备在非阻塞模式下调用connect函数2.调用connect，正常情况下，因为TCP三次握手需要一些时间；而非阻塞调用只要不能立即完成就会返回错误，所以这里会返回EINPROGRESS，表示在建立连接但还没有完成。
3.在读套接口描述符集(fd_set rset)和写套接口描述符集(fd_set wset)中将当前套接口置位（用FD_ZERO()、FD_SET()宏），并设置好超时时间(struct timeval *timeout)
4.调用select( socket, &rset, &wset, NULL, timeout )
返回0表示connect超时
如果你设置的超时时间大于75秒就没有必要这样做了，因为内核中对connect有超时限制就是75秒。
#include<stdio.h>#include<stdlib.h>
#include<signal.h>
#include<unistd.h>
#include<netinet/ip_icmp.h>
#include<netdb.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/time.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<pthread.h>
struct sockaddr_in dst_addr
struct sockaddr_in recv_addr
struct timeval tvrecv
char icmp_pkt[1024] = {0}
char recv_pkt[1024] = {0}
int sockfd = 0, bytes = 56, nsend_pkt = 0, nrecv_pkt = 0
pid_t pid
void statistics()
int in_chksum(unsigned short *buf, int size)
int pack(int send_pkt)
void *send_ping()
int unpack(char *recv_pkt, int size)
void *recv_ping()
void tv_sub(struct timeval *out,struct timeval *in)
int main(int argc, char **argv)
{
int size = 50 * 1024
int errno = -1
int ttl = 64
void *tret
pthread_t send_id,recv_id
struct in_addr ipv4_addr
struct hostent *ipv4_host
struct protoent *protocol = NULL
if (argc < 2)
{
printf("usage: ./ping <host>\n")
return -1
}
if ((protocol = getprotobyname("icmp")) == NULL)
{
printf("unkown protocol\n")
return -1
}
if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0)
{
printf("socket fail\n")
return -1
}
setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size))
setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl))
setsockopt(sockfd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl))
memset(&dst_addr, 0, sizeof(dst_addr))
dst_addr.sin_family = AF_INET
errno = inet_aton(argv[1], &ipv4_addr)
if (errno == 0)
{
ipv4_host = gethostbyname(argv[1])
if (NULL == ipv4_host)
{
printf("connect: Invalid argument\n")
return -1
}
memcpy(&(dst_addr.sin_addr), ipv4_host->h_addr, sizeof(struct in_addr))
}
else
{
memcpy(&(dst_addr.sin_addr), &(ipv4_addr.s_addr), sizeof(struct in_addr))
}
pid = getpid()
printf("PING %s (%s) %d bytes of data.\n",argv[1], inet_ntoa(dst_addr.sin_addr), bytes)
signal(SIGINT, statistics)
errno = pthread_create(&send_id, NULL, send_ping, NULL)
if (errno != 0)
{
printf("send_ping thread fail\n")
return -1
}
errno = pthread_create(&recv_id, NULL, recv_ping, NULL)
if (errno != 0)
{
printf("recv_ping thread fail\n")
return -1
}
pthread_join(send_id, &tret)
pthread_join(recv_id, &tret)
return 0
}
void statistics()
{
printf("\n--- %s ping statistics ---\n", inet_ntoa(dst_addr.sin_addr))
printf("%d packets transmitted, %d received, %.3f%c packet loss\n",
nsend_pkt, nrecv_pkt, (float)100*(nsend_pkt - nrecv_pkt)/nsend_pkt, '%')
close(sockfd)
exit(0)
}
int in_chksum(unsigned short *buf, int size)
{
int nleft = size
int sum = 0
unsigned short *w = buf
unsigned short ans = 0
while(nleft > 1)
{
sum += *w++
nleft -= 2
}
if (nleft == 1)
{
*(unsigned char *) (&ans) = *(unsigned char *)w
sum += ans
}
sum = (sum >> 16) + (sum & 0xFFFF)
sum += (sum >> 16)
ans = ~sum
return ans
}
int pack(int send_pkt)
{
struct icmp *pkt = (struct icmp *)icmp_pkt
struct timeval *time = NULL
pkt->icmp_type = ICMP_ECHO
pkt->icmp_cksum = 0
pkt->icmp_seq = htons(nsend_pkt)
pkt->icmp_id = pid
time = (struct timeval *)pkt->icmp_data
gettimeofday(time, NULL)
pkt->icmp_cksum = in_chksum((unsigned short *)pkt, bytes + 8)
return bytes + 8
}
void *send_ping()
{
int send_bytes = 0
int ret = -1
while(1)
{
nsend_pkt++
send_bytes = pack(nsend_pkt)
ret = sendto(sockfd, icmp_pkt, send_bytes, 0, (struct sockaddr *)&dst_addr, sizeof(dst_addr))
if (ret == -1)
{
printf("send fail\n")
sleep(1)
continue
}
sleep(1)
}
}
void tv_sub(struct timeval *out,struct timeval *in)
{
if ((out->tv_usec-=in->tv_usec) < 0)
{
--out->tv_sec
out->tv_usec += 1000000
}
out->tv_sec -= in->tv_sec
}
int unpack(char *recv_pkt, int size)
{
struct iphdr *ip = NULL
int iphdrlen
struct icmp *icmp
struct timeval *tvsend
double rtt
ip = (struct iphdr *)recv_pkt
iphdrlen = ip->ihl<<2
icmp = (struct icmp *)(recv_pkt + iphdrlen)
size -= iphdrlen
if (size < 8)
{
printf("ICMP size is less than 8\n")
return -1
}
if ((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid))
{
tvsend = (struct timeval *)icmp->icmp_data
tv_sub(&tvrecv, tvsend)
rtt = tvrecv.tv_sec * 1000 + (double)tvrecv.tv_usec / (double)1000
printf("%d byte from %s: icmp_seq = %d ttl=%d rtt=%.3fms\n",
size,inet_ntoa(recv_addr.sin_addr),ntohs(icmp->icmp_seq), ip->ttl, rtt)
}
else
{
return -1
}
return 0
}
void *recv_ping()
{
fd_set rd_set
struct timeval time
time.tv_sec = 5
time.tv_usec = 0
int ret = 0, nread = 0,recv_len = 0
recv_len = sizeof(recv_addr)
while(1)
{
FD_ZERO(&rd_set)
FD_SET(sockfd, &rd_set)
ret = select(sockfd + 1, &rd_set, NULL, NULL, &time)
if (ret <= 0)
{
continue
}
else if (FD_ISSET(sockfd, &rd_set))
{
nread = recvfrom(sockfd, recv_pkt, sizeof(recv_pkt), 0, (struct sockaddr *)&recv_addr,(socklen_t *) &recv_len)
if (nread < 0)
{
continue
}
gettimeofday(&tvrecv, NULL)
if (unpack(recv_pkt, nread) == -1)
{
continue
}
nrecv_pkt++
}
}
}
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