[완료]raw socket 관련문제입니다,,

/*
제가 생각한 방법은 buffer에는 ip+icmp 헤더를 넣어서 전송하고 그전에 nbuffer에 ip헤더(fragmentaion)을 
전송하는 방법입니다. 코드에 나왔있지만 offset은 제대로 맞춘상태고 wireshark로 보았을때 의도한대로
나오네요. 그냥 buffer와 nbuffer는 배열로 선언했습니다,, request도 가지 않는 상황이기에 recvfrom 은 구현해 놓지 않았습니다 
제 허접한 코드입니다*/
 
 
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <errno.h>
#include <unistd.h>
#include <netinet/ip_icmp.h>
unsigned short in_cksum(unsigned short *,int len);
int main(int argc,char **argv){
if(argc!=3){
printf("USAGE %s [dest IP] [source ip]\n",argv[0]);
exit(1);
}
 
	int nsock,clnt_size,size;
	int on=1,i=0,len;
	char buffer[1480];
        struct ip *iphdr;
	struct in_addr ex_addr;
        struct icmp *icmp;
        struct sockaddr_in serv_sock;
	char nbuffer[1480];
 
nsock=socket(AF_INET,SOCK_RAW,IPPROTO_ICMP);
if(nsock<0){
printf("socket connect error\n");
exit(1);
}
 
setsockopt(nsock, IPPROTO_IP, IP_HDRINCL, (char *)&on, sizeof(on) );
 
bzero(&serv_sock,sizeof(serv_sock)); 
serv_sock.sin_family=AF_INET; 
serv_sock.sin_addr.s_addr=inet_addr(argv[1]); 
 
//nbuffer 시작
memset(nbuffer,0x0,1480);
iphdr=(struct ip*)(nbuffer);
iphdr->ip_v=4; 
iphdr->ip_hl=5; 
iphdr->ip_p=IPPROTO_ICMP;//IPPROTO_TCP; 
iphdr->ip_len=htons(1480); 
iphdr->ip_id=20; 
iphdr->ip_ttl=125; 
iphdr->ip_off=htons(IP_MF);
iphdr->ip_sum=0;
iphdr->ip_tos=0x000;
ex_addr.s_addr=inet_addr(argv[2]);
iphdr->ip_src=ex_addr; 
ex_addr.s_addr=inet_addr(argv[1]);
iphdr->ip_dst=ex_addr; 
iphdr->ip_sum=in_cksum((unsigned short *)iphdr,sizeof(struct iphdr)); //ip header end 
//nbuffer 끝
 
//buffer 시작
iphdr=(struct ip*)(buffer);
iphdr->ip_v=4; 
iphdr->ip_hl=5; 
iphdr->ip_p=IPPROTO_ICMP;//IPPROTO_TCP; 
iphdr->ip_len=htons(1480); 
iphdr->ip_id=20; 
iphdr->ip_ttl=125;
iphdr->ip_off=htons(185);
iphdr->ip_sum=0;
iphdr->ip_tos=0x000;
ex_addr.s_addr=inet_addr(argv[2]);
iphdr->ip_src=ex_addr; 
ex_addr.s_addr=inet_addr(argv[1]);
iphdr->ip_dst=ex_addr; 
iphdr->ip_sum=in_cksum((unsigned short *)iphdr,sizeof(struct iphdr)); //ip header end 
 
icmp=(struct icmp*)(buffer+sizeof(struct ip)); 
icmp->icmp_type=ICMP_ECHO;//ICMP_UNREACH; 
icmp->icmp_code=0; 
icmp->icmp_cksum=0; 
icmp->icmp_seq=15; 
icmp->icmp_id=20;   
icmp->icmp_cksum=in_cksum((unsigned short*)icmp,900); 
//buffer 끝
sendto(nsock,nbuffer,sizeof(nbuffer),0x0,(struct sockaddr*)&serv_sock,sizeof(serv_sock));
sendto(nsock,buffer,sizeof(buffer),0x0,(struct sockaddr*)&serv_sock,sizeof(serv_sock));
}
 
unsigned short in_cksum(unsigned short *addr,int len)
{
    register int sum = 0;
    u_short answer = 0;
    register u_short *w = addr;
    register int nleft = len;
 
    /*
    * Our algorithm is simple, using a 32 bit accumulator (sum), we add
    * sequential 16 bit words to it, and at the end, fold back all the
    * carry bits from the top 16 bits into the lower 16 bits.
    */
    while(nleft > 1)  {
        sum += *w++;
        nleft -= 2;
    }
 
    /* mop up an odd byte, if necessary */
    if(nleft == 1) {
        *(u_char *)(&answer) = *(u_char *)w ;
        sum += answer;
    }
 
    /* add back carry outs from top 16 bits to low 16 bits */
    sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
    sum += (sum >> 16);                     /* add carry */
    answer = ~sum;                          /* truncate to 16 bits */
    return(answer);
}