Hi,
I want to build a packet with a source IP address and dest ip address (
usual case ) given by me and the protocol field in the IP hdr is a
unassigned protocol number ( i used 140 ). I built the IP header by
opening a RAW socket and by setting the IP_HDRINCL option. The source IP
address i gave is not the IP address in any of the interfaces of my
machine. ( I gave 1.2.3.4 ). I bind the raw socket to a local interface
( my ip address is 192.168.100.242 ) and sent the packet using sendto.
Now in my same machine, i did another program to collect and display the
packet sent my me to my interface itself. This program will also open a
ra socket with protocol field as IPPROTO_RAW and i used recvfrom to
receive the message. But i am not receiving the message. I am missing
somewhere. I could not figure it out. I pasted the code here. Kindly
have a look into it and tell me where am missing. I will be very much
thankful. here is the code.
=====================================================
This program is the one am building the IP packet.
====================================================
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <errno.h>
#define PORT 0
#define PROTOCOL 140
#define LOCAL_IP_ADDR "192.168.100.242"
#define DEST_IP_ADDR "192.168.100.242"
#define MESSAGE "This is the packet from 1.2.3.4 IP address" /*this
message is encapsulated by my IP hdr */
extern uint16_t checksum(uint16_t *,uint32_t );
extern int build_iphdr(void *,uint32_t );
main() {
int raw,sockopt_val=1;
struct sockaddr_in local_addr,peer_addr;
struct iphdr *ip;
char *my_sending_pkt;
if( (raw=socket(AF_INET,SOCK_RAW,IPPROTO_RAW)) < 0 ) {
perror("sock");
exit(1);
}
if( (my_sending_pkt=(char *)malloc(sizeof(struct iphdr)+sizeof(MESSAGE))
) == NULL ) {
perror("Calloc failed:");
exit(1);
}
ip=(struct iphdr *)my_sending_pkt;
strcpy( (my_sending_pkt+sizeof(struct iphdr)),MESSAGE);
bzero(&local_addr,sizeof(local_addr));
bzero(&peer_addr,sizeof(peer_addr));
local_addr.sin_family=AF_INET;
local_addr.sin_port=htons(PORT);
peer_addr.sin_family=AF_INET;
peer_addr.sin_port=htons(PORT);
if( (inet_aton(LOCAL_IP_ADDR,&local_addr.sin_addr.s_addr)) == 0 ) {
perror("Addr conversion:");
exit(1);
}
if( (inet_aton(DEST_IP_ADDR,&peer_addr.sin_addr.s_addr)) == 0 ) {
perror("Addr conversion:");
exit(1);
}
if( (setsockopt(raw,SOL_IP,IP_HDRINCL,&sockopt_val,(socklen_t
)sizeof(sockopt_val)) ) < 0 ) {
perror("setsockopt:");
exit(errno);
}
if( (build_iphdr(ip,sizeof(MESSAGE)) ) < 0 ) {
perror("Build IP failed:");
exit(1);
}
if( ( bind(raw,(struct sockaddr *)&local_addr,(socklen_t
)sizeof(local_addr)) ) < 0 ) {
perror("Bind:");
exit(1);
}
if( (sendto(raw,my_sending_pkt, (sizeof(struct
iphdr)+sizeof(MESSAGE)),0,(struct sockaddr *)&peer_addr
,(socklen_t)sizeof(peer_addr)) ) < 0 ) {
perror("Sendto failed:");
exit(1);
}
}
======================================================
The following code contains the api's build_iphdr and Checksum.
====================================================
/* this file contains the functions used for building IP packets */
#include <netinet/ip.h>
#include <netinet/in.h>
/*#include "lmptypes.h"*/ /* My hdr where the data types are type
defined */
/* #define SIZE 22 Since i am going to send the message "this is
1.2.3.4 packet" */
#define SOURCE_IP "1.2.3.4"
#define DEST_IP "192.168.100.242"
uint16_t checksum(uint16_t *data,uint32_t len) {
/* data is the one for which we are calculating checksum and its size
len in bytes */
register uint32_t sum=0;
uint16_t ans;
register uint16_t *temp=data;
register uint32_t odd = len;
/* adding 16 bits every time to sum */
while( odd > 1) {
sum += *temp;
odd -= 2;
}
/* if length is odd the last 8 bits will also get added here */
if( odd )
sum += *(uint8_t *)temp;
sum=(sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
ans=~sum; /* truncating to 16 bits */
return (ans);
}
int build_iphdr(void *buffer, uint32_t len) {
/* Pointer to the allocated buffer for IP hdr structure. len is the
length if the data to be encap in IP */
/* In this fn the tot length field is data len + ip hdr length */
/* id will be the current user id running the process */
struct iphdr *ip=buffer;
/*
if( (ip=(struct iphdr *)calloc(1,sizeof(struct iphdr)) ) == NULL ) {
perror("calloc failed:");
return -1;
}
*/
ip->version=4;
ip->ihl=5;
ip->tos=0;
ip->tot_len=sizeof(struct iphdr) + len;
ip->id=htons(getuid());
ip->ttl=255;
ip->protocol=htons(140); /*My protocol number to check LMP */
if( (ip->saddr=inet_addr(SOURCE_IP)) < 0 ) {
perror("Give valid source IP:");
return -1;
}
if( (ip->daddr=inet_addr(DEST_IP)) < 0 ) {
perror("Give valid dest IP:");
return -1;
}
ip->check=checksum((unsigned short *)ip,sizeof(struct iphdr));
return 0;
}
=======================================================
The following is the code which is waiting to receive the IP packet
what i sent. The display api will display the content of the packet and
i want to
see the IP address 1.2.3.4 here. But its not receiving the packet
=======================================================
#include <netinet/in.h>
#include <netinet/ip.h>
#include <stdio.h>
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
void display(void *buf, int bytes)
{ int i;
struct iphdr *ip = buf;
printf("----------------\n");
for ( i = 0; i < bytes; i++ )
{
if ( !(i & 15) ) printf("\n%04X: ", i);
printf("%02X ", ((unsigned char*)buf)[i]);
}
printf("\n");
printf("IPv%d: hdr-size=%d pkt-size=%d protocol=%d TTL=%d src=%s ",
ip->version, ip->ihl*4, ntohs(ip->tot_len), ip->protocol,
ip->ttl, inet_ntoa(ip->saddr));
printf("dst=%s\n", inet_ntoa(ip->daddr));
}
main()
{ int sd,sock_opt=1;
struct sockaddr_in addr;
unsigned char buf[1024];
sd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
if ( sd < 0 )
{
perror("socket");
exit(0);
}
if( fcntl(sd,F_SETFL,O_NONBLOCK) != 0 ) {
perror("NON block IO fail:");
exit(1);
}
for (;;)
{ int bytes, len=sizeof(addr);
bzero(buf, sizeof(buf));
bytes = recvfrom(sd, buf, sizeof(buf), 0, (struct sockaddr *)&addr,
&len);
if ( bytes > 0 )
display(buf, bytes);
}
exit(0);
}
======================================================
Kindly help me where am missing.
Thanks
Ramesh
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