Creating ip network packets

Question

I have to create my own network packets manually Using any Protocol.i should send it to the client and parse or analyse the packet.Can any1 help me out with where and hpw to start ??? I have idea about socket programming..

Answer 1

你可以使用<linux/ip.h>它包含的结构来指向ip包.你也可以使用socket.

这里是一个例子.此示例发送ICMP ECHO数据包并等待响应

/* send icmp packet example */
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <linux/ip.h>
#include <linux/icmp.h>

int main(int argc, char* argv[])
{
    struct iphdr *ip, *ip_reply;
    struct icmphdr* icmp;
    struct sockaddr_in connection;
    char *dst_addr="192.168.1.33";
    char *src_addr="192.168.1.34";
    char *packet, *buffer;
    int sockfd, optval, addrlen;

    packet = malloc(sizeof(struct iphdr) + sizeof(struct icmphdr));
    buffer = malloc(sizeof(struct iphdr) + sizeof(struct icmphdr));
    ip = (struct iphdr*) packet;
    icmp = (struct icmphdr*) (packet + sizeof(struct iphdr));

    ip->ihl         = 5;
    ip->version     = 4;
    ip->tot_len     = sizeof(struct iphdr) + sizeof(struct icmphdr);
    ip->protocol    = IPPROTO_ICMP;
    ip->saddr       = inet_addr(src_addr);
    ip->daddr       = inet_addr(dst_addr);
    ip->check = in_cksum((unsigned short *)ip, sizeof(struct iphdr)); 

    icmp->type      = ICMP_ECHO;
    icmp->checksum = in_cksum((unsigned short *)icmp, sizeof(struct icmphdr));

    /* open ICMP socket */
    if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1) {
        perror("socket");
        exit(EXIT_FAILURE);
    }
     /* IP_HDRINCL must be set on the socket so that the kernel does not attempt 
     *  to automatically add a default ip header to the packet*/
    setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &optval, sizeof(int));

    connection.sin_family       = AF_INET;
    connection.sin_addr.s_addr  = ip->daddr;
    sendto(sockfd, packet, ip->tot_len, 0, (struct sockaddr *)&connection, sizeof(struct sockaddr));
    printf("Sent %d byte packet to %s\n", ip->tot_len, dst_addr);

    addrlen = sizeof(connection);
    if (recvfrom(sockfd, buffer, sizeof(struct iphdr) + sizeof(struct icmphdr), 0, (struct sockaddr *)&connection, &addrlen) == -1)
        {
        perror("recv");
        }
    else
        {
        char *cp;
        ip_reply = (struct iphdr*) buffer;
        cp = (char *)&ip_reply->saddr;
        printf("Received %d byte reply from %u.%u.%u.%u:\n", ntohs(ip_reply->tot_len), cp[0]&0xff,cp[1]&0xff,cp[2]&0xff,cp[3]&0xff);
        printf("ID: %d\n", ntohs(ip_reply->id));
        printf("TTL: %d\n", ip_reply->ttl);
        }

}

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);
}