#include

#include

#include

#include

#include

#include

#include

#include

$//$ The IP header's structure

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 short int iph$\_$flags$\_$offset;

unsigned char iph$\_$ttl;

unsigned char iph$\_$protocol;

unsigned short int iph$\_$chksum;

unsigned int iph$\_$sourceip;

unsigned int iph$\_$destip;

$\}$;

$//$ Simple checksum function, might be needed for some headers

unsigned short csum$($unsigned short $*$buf$,$ int nwords$)\{$

unsigned long sum;

for $($sum $=0$; nwords $>0$; nwords$--)$

sum $+=*$buf$++$;

sum $=($sum $>>16)+($sum & $0$xffff$)$;

sum $+=($sum $>>16)$;

return $($unsigned short$)($~sum$)$;

$\}$

int main$()\{$

int sd;

char buffer$[4096]$;

struct ipheader $*$ip $=($struct ipheader $*)$ buffer;

struct icmphdr $*$icmp $=($struct icmphdr $*)($buffer $+$ sizeof$($struct ipheader$))$;

char $*$data $=$ buffer $+$ sizeof$($struct ipheader$)+$ sizeof$($struct icmphdr$)$;

$//$ Create a raw socket with IP protocol.

sd $=$ socket$($AF$\_$INET, SOCK$\_$RAW, IPPROTO$\_$RAW$)$;

if $($sd $<0)\{$

perror$("$socket$()$ error"$)$;

exit$(-1)$;

$\}$

$//$ Set the fields in the IP header

ip$->$iph$\_$ver $=4$; $//$ Version

ip$->$iph$\_$ihl $=5$; $//$ IHL

ip$->$iph$\_$tos $=0$; $//$ Type of service

ip$->$iph$\_$len $=$ htons$($sizeof$($struct ipheader$)+$ sizeof$($struct icmphdr$)+$ strlen$($data$))$; $//$ Include IP header, ICMP header, and data length in total length

ip$->$iph$\_$ident $=$ htons$(54321)$; $//$ Identification

ip$->$iph$\_$flags$\_$offset $=$ htons$(0$x$4000)$; $//$ Don't fragment flag, $0$ offset

ip$->$iph$\_$ttl $=255$; $//$ Time to live

ip$->$iph$\_$protocol $=$ IPPROTO$\_$ICMP; $//$ Protocol

ip$->$iph$\_$chksum $=0$; $//$ Checksum $($temporarily set to $0)$

ip$->$iph$\_$sourceip $=$ inet$\_$addr$("1\mathrm{.}2\mathrm{.}3\mathrm{.}8")$; $//$ Spoofed source IP address

ip$->$iph$\_$destip $=$ inet$\_$addr$("10\mathrm{.}9\mathrm{.}0\mathrm{.}6")$; $//$ Destination IP address

$//$ Set the fields in the ICMP header

icmp$->$type $=$ ICMP$\_$ECHO;

icmp$->$code $=0$;

icmp$->$checksum $=0$; $//$ Checksum $($temporarily set to $0)$

icmp$->$un$.$echo.id $=1234$;

icmp$->$un$.$echo.sequence $=0$;

$//$ Copy the message into the buffer after the ICMP header

strcpy$($data$,$ "Hello"$)$;

$//$ Calculate the IP checksum now that the header is filled out

ip$->$iph$\_$chksum $=$ csum$(($unsigned short $*)$buffer$,$ sizeof$($struct ipheader$)+$ sizeof$($struct icmphdr$)+$ strlen$($data$))$;

$//$ Inform the kernel that headers are included in the packet

int one $=1$;

const int $*$val $=$ &one;

if $($setsockopt$($sd$,$ IPPROTO$\_$IP$,$ IP$\_$HDRINCL, val, sizeof$($one$))<0)\{$

perror$("$setsockopt$()$ error"$)$;

exit$(-1)$;

$\}$

$//$ Destination address structure

struct sockaddr$\_$in sin;

sin$.$sin$\_$family $=$ AF$\_$INET;

sin$.$sin$\_$port $=$ htons$(0)$; $//$ Port number $($not needed for ICMP$)$

sin$.$sin$\_$addr.s$\_$addr $=$ ip$->$iph$\_$destip;

$//$ Send the packet

if $($sendto$($sd$,$ buffer, ntohs$($ip$->$iph$\_$len$),0,($struct sockaddr $*)$&sin$,$ sizeof$($sin$))<0)\{$

perror$("$sendto$()$ error"$)$;

exit$(-1)$;

$\}$

close$($sd$)$;

return $0$;

$\}$ in this code why icmp response is not coming please modify the code properly to handle icmp request and response