Sending and Receiving IP Packet

sindhu4sind · 04-20-2012, 02:06 PM

Hello everyone,

I am new with programming for networking in Linux. I know about the basics of making kernel modules and some of the concepts of related to my work (recently studied). I am working on a project where i don't have any experience but i am trying and looking from forums.

My supervisor asked me to make a program to send IP packet to the other network.

I want to struct a packet and send it from source to destination.

I have no idea about how to do this. any body can suggest me any sample program for this? I searched on internet but may be i am not well known of this field so i couldn't use the proper terms for searching. if you guys can suggest me some links related to this work than this will be great help for me..

As this is my startup in new field, so i would prefer to follow a a complete example that i can get whats going on each step. It would be better for my future work in this project.
thanks

btmiller · 04-21-2012, 12:54 AM

Do you have to do this in kernel mode? It would be simpler to use user mode socket programming. There's lots of good documentation to do it there.

I don't know much about kernel level network programming, so I'd advise checking out the networking chapters of a Linux kernel book -- I've been partial to Robert Love's books, personally.

sindhu4sind · 04-21-2012, 04:29 AM

Thank you btmiller.

and i have found a way to struct ip header and udp header and to send the packet from source to destination, for starting i think it is a good step. but i am facing a problem, after i send packet to loopback i dont receive it using sniffer.c. I am worried that either it is possible to receive sent packets on loop back or not!? if it is possible to send then why i am not receiving packet count there.

////////////////////here is my code///////////////////

Quote:

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/udp.h>

#define PCKT_LEN 8192

//Create the IP header
struct ipheader {
unsigned char iph_ihl:4, iph_ver:4;
unsigned char iph_tos;
unsigned short int iph_len;
unsigned short int iph_ident;
unsigned char iph_flags;
unsigned short int iph_offset;
unsigned char iph_ttl;
unsigned char iph_protocol;
unsigned short int iph_chksum;
unsigned int iph_sourceip;
unsigned int iph_destip;
};

//Create the UDP Header
struct udpheader {
unsigned short int udph_srcport;
unsigned short int udph_destport;
unsigned short int udph_len;
unsigned short int udph_chksum;
}; /* total udp header length: 8 bytes (= 64 bits) */

// Function for checksum calculation
unsigned short csum(unsigned short *buf, int nwords)
{ //
unsigned long sum;
for(sum=0; nwords>0; nwords--)
sum += *buf++;
sum = (sum >> 16) + (sum &0xffff);
sum += (sum >> 16);
return (unsigned short)(~sum);
}

// Source IP, source port, target IP, target port from command line
int main(int argc, char *argv[]){
int sd;
char buffer[PCKT_LEN];
struct ipheader *ip = (struct ipheader *) buffer;
struct udpheader *udp = (struct udpheader *) (buffer + sizeof(struct ipheader));

// Source and destination addresses: IP and port
struct sockaddr_in sin, din;
int one = 1;
const int *val = &one;
memset(buffer, 0, PCKT_LEN);

//
if(argc != 5)
{
printf("- Invalid parameters!!!\n");
printf("- Usage %s <source hostname/IP> <source port> <target hostname/IP> <target port>\n", argv[0]);
exit(-1);
}

// Create a raw socket with UDP protocol
sd = socket (PF_INET, SOCK_RAW, IPPROTO_UDP);

if (sd < 0)
{
perror("socket() error");
exit (-1);
}
else
printf("socket() - UDP and using raw socket is OKAY");

// Address family
sin.sin_family = AF_INET;
din.sin_family = AF_INET;

//port numbers
sin.sin_port = htons(atoi(argv[2]));
din.sin_port = htons(atoi(argv[4]));

// Fabricate the IP header
ip->iph_ihl = 5;
ip->iph_ver = 4;
ip->iph_tos = 16; // Low delay
ip->iph_len = sizeof(struct ipheader) + sizeof(struct udpheader);
ip->iph_ident = htons(54321);
ip->iph_ttl = 64; // hops
ip->iph_protocol = 17; // UDP
ip->iph_sourceip = inet_addr(argv[1]); // source IP address
ip->iph_destip = inet_addr(argv[3]); // destination IP header

// Fabricate the UDP header
udp->udph_srcport=htons (atoi(argv[2]));
udp->udph_destport = htons(atoi(argv[4]));
udp->udph_len = htons(sizeof(struct udpheader));
ip->iph_chksum = csum((unsigned short *)buffer, sizeof(struct ipheader) + sizeof(struct udpheader));

// Inform the kernel do not fill up the packet structure
if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0)
{
perror("socketpot() error");
exit (-1);
}

else
printf("socketpot() is OKAY");

printf("trying...\n");
printf("Using raw socket and UDP protocol\n");
printf("Using Source IP: %s port: %u, Target IP: %s port: %u.\n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));

int count;

for(count = 1; count <=20; count++)
{
if(sendto(sd, buffer, ip->iph_len, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0)
{
perror("sendto() error");// Verify
exit(-1);
}
else
{
printf("Count #%u - sendto() is OK.\n", count);
sleep(2);
}
}
close (sd);
return 0;
}

This is perfectly fine, and sending 20 packets. But unfortunately in monitoring the packet reception i don't receive any packet for loopback.
NOTE: I am using this format for loopback correct me if i am wrong anywhere:

Quote:

# ./myProgram 127.0.0.1 22 127.127.0.0.1 8008

i have also tried give same port number for both also but its not working in that way which i want.

I am newbie if i am making some stupid mistake then please make me correct..