To install libpcap on your linux distro you can either download the source from the website and compile it and install. Or if you are on a distro like ubuntu then it can be installed from synaptic package manager. In the list of packages in Synaptic Package Manager look for 2 packages named as libpcap0.8 and libpcap0.8-dev. Install both of them.
find_alldevs() is the function which can be used to get a list of all available network devices or interfaces present on the machine or which can be opened by pcap_open_live() for sniffing purpose.
where alldevsp is a pointer to an array of of pcap_if_t structures and errbuf is a character pointer and will contain any error message that occured during the function call.
pcap_open_live() is the function to get a packet capture descriptor or a handle to a device which has been opened up for sniffing. The protoype is as :
pcap_t *pcap_open_live(const char *device, int snaplen,int promisc, int to_ms, char *errbuf)
device – is the name of the device as obtained from the call to pcap_findalldevs.
snaplen – is the maximum amount of data to be captured. 65536 should be sufficient length.
promisc – 0 or 1 to indicate whether to open the device in promiscuous mode.
to_ms – the timeout in milliseconds , 0 for no timeout
errbuf – buffer to contain any error message
It returns a device handler in the form of the structure pcap_t which can be used by pcap_loop() to capture data from.
/*
Packet sniffer using libpcap library
*/
#include<pcap.h>
#include<stdio.h>
#include<stdlib.h> // for exit()
#include<string.h> //for memset
#include<sys/socket.h>
#include<arpa/inet.h> // for inet_ntoa()
#include<net/ethernet.h>
#include<netinet/ip_icmp.h> //Provides declarations for icmp header
#include<netinet/udp.h> //Provides declarations for udp header
#include<netinet/tcp.h> //Provides declarations for tcp header
#include<netinet/ip.h> //Provides declarations for ip header
void process_packet(u_char *, const struct pcap_pkthdr *, const u_char *);
void process_ip_packet(const u_char * , int);
void print_ip_packet(const u_char * , int);
void print_tcp_packet(const u_char * , int );
void print_udp_packet(const u_char * , int);
void print_icmp_packet(const u_char * , int );
void PrintData (const u_char * , int);
FILE *logfile;
struct sockaddr_in source,dest;
int tcp=0,udp=0,icmp=0,others=0,igmp=0,total=0,i,j;
int main()
{
pcap_if_t *alldevsp , *device;
pcap_t *handle; //Handle of the device that shall be sniffed
char errbuf[100] , *devname , devs[100][100];
int count = 1 , n;
//First get the list of available devices
printf("Finding available devices ... ");
if( pcap_findalldevs( &alldevsp , errbuf) )
{
printf("Error finding devices : %s" , errbuf);
exit(1);
}
printf("Done");
//Print the available devices
printf("\nAvailable Devices are :\n");
for(device = alldevsp ; device != NULL ; device = device->next)
{
printf("%d. %s - %s\n" , count , device->name , device->description);
if(device->name != NULL)
{
strcpy(devs[count] , device->name);
}
count++;
}
//Ask user which device to sniff
printf("Enter the number of the device you want to sniff : ");
scanf("%d" , &n);
devname = devs[n];
//Open the device for sniffing
printf("Opening device %s for sniffing ... " , devname);
handle = pcap_open_live(devname , 65536 , 1 , 0 , errbuf);
if (handle == NULL)
{
fprintf(stderr, "Couldn't open device %s : %s\n" , devname , errbuf);
exit(1);
}
printf("Done\n");
logfile=fopen("log.txt","w");
if(logfile==NULL)
{
printf("Unable to create file.");
}
//Put the device in sniff loop
pcap_loop(handle , -1 , process_packet , NULL);
return 0;
}
void process_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *buffer)
{
int size = header->len;
//Get the IP Header part of this packet , excluding the ethernet header
struct iphdr *iph = (struct iphdr*)(buffer + sizeof(struct ethhdr));
++total;
switch (iph->protocol) //Check the Protocol and do accordingly...
{
case 1: //ICMP Protocol
++icmp;
print_icmp_packet( buffer , size);
break;
case 2: //IGMP Protocol
++igmp;
break;
case 6: //TCP Protocol
++tcp;
print_tcp_packet(buffer , size);
break;
case 17: //UDP Protocol
++udp;
print_udp_packet(buffer , size);
break;
default: //Some Other Protocol like ARP etc.
++others;
break;
}
printf("TCP : %d UDP : %d ICMP : %d IGMP : %d Others : %d Total : %d\r", tcp , udp , icmp , igmp , others , total);
}
void print_ethernet_header(const u_char *Buffer, int Size)
{
struct ethhdr *eth = (struct ethhdr *)Buffer;
fprintf(logfile , "\n");
fprintf(logfile , "Ethernet Header\n");
fprintf(logfile , " |-Destination Address : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X \n", eth->h_dest[0] , eth->h_dest[1] , eth->h_dest[2] , eth->h_dest[3] , eth->h_dest[4] , eth->h_dest[5] );
fprintf(logfile , " |-Source Address : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X \n", eth->h_source[0] , eth->h_source[1] , eth->h_source[2] , eth->h_source[3] , eth->h_source[4] , eth->h_source[5] );
fprintf(logfile , " |-Protocol : %u \n",(unsigned short)eth->h_proto);
}
void print_ip_header(const u_char * Buffer, int Size)
{
print_ethernet_header(Buffer , Size);
unsigned short iphdrlen;
struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr) );
iphdrlen =iph->ihl*4;
memset(&source, 0, sizeof(source));
source.sin_addr.s_addr = iph->saddr;
memset(&dest, 0, sizeof(dest));
dest.sin_addr.s_addr = iph->daddr;
fprintf(logfile , "\n");
fprintf(logfile , "IP Header\n");
fprintf(logfile , " |-IP Version : %d\n",(unsigned int)iph->version);
fprintf(logfile , " |-IP Header Length : %d DWORDS or %d Bytes\n",(unsigned int)iph->ihl,((unsigned int)(iph->ihl))*4);
fprintf(logfile , " |-Type Of Service : %d\n",(unsigned int)iph->tos);
fprintf(logfile , " |-IP Total Length : %d Bytes(Size of Packet)\n",ntohs(iph->tot_len));
fprintf(logfile , " |-Identification : %d\n",ntohs(iph->id));
//fprintf(logfile , " |-Reserved ZERO Field : %d\n",(unsigned int)iphdr->ip_reserved_zero);
//fprintf(logfile , " |-Dont Fragment Field : %d\n",(unsigned int)iphdr->ip_dont_fragment);
//fprintf(logfile , " |-More Fragment Field : %d\n",(unsigned int)iphdr->ip_more_fragment);
fprintf(logfile , " |-TTL : %d\n",(unsigned int)iph->ttl);
fprintf(logfile , " |-Protocol : %d\n",(unsigned int)iph->protocol);
fprintf(logfile , " |-Checksum : %d\n",ntohs(iph->check));
fprintf(logfile , " |-Source IP : %s\n" , inet_ntoa(source.sin_addr) );
fprintf(logfile , " |-Destination IP : %s\n" , inet_ntoa(dest.sin_addr) );
}
void print_tcp_packet(const u_char * Buffer, int Size)
{
unsigned short iphdrlen;
struct iphdr *iph = (struct iphdr *)( Buffer + sizeof(struct ethhdr) );
iphdrlen = iph->ihl*4;
struct tcphdr *tcph=(struct tcphdr*)(Buffer + iphdrlen + sizeof(struct ethhdr));
int header_size = sizeof(struct ethhdr) + iphdrlen + tcph->doff*4;
fprintf(logfile , "\n\n***********************TCP Packet*************************\n");
print_ip_header(Buffer,Size);
fprintf(logfile , "\n");
fprintf(logfile , "TCP Header\n");
fprintf(logfile , " |-Source Port : %u\n",ntohs(tcph->source));
fprintf(logfile , " |-Destination Port : %u\n",ntohs(tcph->dest));
fprintf(logfile , " |-Sequence Number : %u\n",ntohl(tcph->seq));
fprintf(logfile , " |-Acknowledge Number : %u\n",ntohl(tcph->ack_seq));
fprintf(logfile , " |-Header Length : %d DWORDS or %d BYTES\n" ,(unsigned int)tcph->doff,(unsigned int)tcph->doff*4);
//fprintf(logfile , " |-CWR Flag : %d\n",(unsigned int)tcph->cwr);
//fprintf(logfile , " |-ECN Flag : %d\n",(unsigned int)tcph->ece);
fprintf(logfile , " |-Urgent Flag : %d\n",(unsigned int)tcph->urg);
fprintf(logfile , " |-Acknowledgement Flag : %d\n",(unsigned int)tcph->ack);
fprintf(logfile , " |-Push Flag : %d\n",(unsigned int)tcph->psh);
fprintf(logfile , " |-Reset Flag : %d\n",(unsigned int)tcph->rst);
fprintf(logfile , " |-Synchronise Flag : %d\n",(unsigned int)tcph->syn);
fprintf(logfile , " |-Finish Flag : %d\n",(unsigned int)tcph->fin);
fprintf(logfile , " |-Window : %d\n",ntohs(tcph->window));
fprintf(logfile , " |-Checksum : %d\n",ntohs(tcph->check));
fprintf(logfile , " |-Urgent Pointer : %d\n",tcph->urg_ptr);
fprintf(logfile , "\n");
fprintf(logfile , " DATA Dump ");
fprintf(logfile , "\n");
fprintf(logfile , "IP Header\n");
PrintData(Buffer,iphdrlen);
fprintf(logfile , "TCP Header\n");
PrintData(Buffer+iphdrlen,tcph->doff*4);
fprintf(logfile , "Data Payload\n");
PrintData(Buffer + header_size , Size - header_size );
fprintf(logfile , "\n###########################################################");
}
void print_udp_packet(const u_char *Buffer , int Size)
{
unsigned short iphdrlen;
struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr));
iphdrlen = iph->ihl*4;
struct udphdr *udph = (struct udphdr*)(Buffer + iphdrlen + sizeof(struct ethhdr));
int header_size = sizeof(struct ethhdr) + iphdrlen + sizeof udph;
fprintf(logfile , "\n\n***********************UDP Packet*************************\n");
print_ip_header(Buffer,Size);
fprintf(logfile , "\nUDP Header\n");
fprintf(logfile , " |-Source Port : %d\n" , ntohs(udph->source));
fprintf(logfile , " |-Destination Port : %d\n" , ntohs(udph->dest));
fprintf(logfile , " |-UDP Length : %d\n" , ntohs(udph->len));
fprintf(logfile , " |-UDP Checksum : %d\n" , ntohs(udph->check));
fprintf(logfile , "\n");
fprintf(logfile , "IP Header\n");
PrintData(Buffer , iphdrlen);
fprintf(logfile , "UDP Header\n");
PrintData(Buffer+iphdrlen , sizeof udph);
fprintf(logfile , "Data Payload\n");
//Move the pointer ahead and reduce the size of string
PrintData(Buffer + header_size , Size - header_size);
fprintf(logfile , "\n###########################################################");
}
void print_icmp_packet(const u_char * Buffer , int Size)
{
unsigned short iphdrlen;
struct iphdr *iph = (struct iphdr *)(Buffer + sizeof(struct ethhdr));
iphdrlen = iph->ihl * 4;
struct icmphdr *icmph = (struct icmphdr *)(Buffer + iphdrlen + sizeof(struct ethhdr));
int header_size = sizeof(struct ethhdr) + iphdrlen + sizeof icmph;
fprintf(logfile , "\n\n***********************ICMP Packet*************************\n");
print_ip_header(Buffer , Size);
fprintf(logfile , "\n");
fprintf(logfile , "ICMP Header\n");
fprintf(logfile , " |-Type : %d",(unsigned int)(icmph->type));
if((unsigned int)(icmph->type) == 11)
{
fprintf(logfile , " (TTL Expired)\n");
}
else if((unsigned int)(icmph->type) == ICMP_ECHOREPLY)
{
fprintf(logfile , " (ICMP Echo Reply)\n");
}
fprintf(logfile , " |-Code : %d\n",(unsigned int)(icmph->code));
fprintf(logfile , " |-Checksum : %d\n",ntohs(icmph->checksum));
//fprintf(logfile , " |-ID : %d\n",ntohs(icmph->id));
//fprintf(logfile , " |-Sequence : %d\n",ntohs(icmph->sequence));
fprintf(logfile , "\n");
fprintf(logfile , "IP Header\n");
PrintData(Buffer,iphdrlen);
fprintf(logfile , "UDP Header\n");
PrintData(Buffer + iphdrlen , sizeof icmph);
fprintf(logfile , "Data Payload\n");
//Move the pointer ahead and reduce the size of string
PrintData(Buffer + header_size , (Size - header_size) );
fprintf(logfile , "\n###########################################################");
}
void PrintData (const u_char * data , int Size)
{
int i , j;
for(i=0 ; i < Size ; i++)
{
if( i!=0 && i%16==0) //if one line of hex printing is complete...
{
fprintf(logfile , " ");
for(j=i-16 ; j<i ; j++)
{
if(data[j]>=32 && data[j]<=128)
fprintf(logfile , "%c",(unsigned char)data[j]); //if its a number or alphabet
else fprintf(logfile , "."); //otherwise print a dot
}
fprintf(logfile , "\n");
}
if(i%16==0) fprintf(logfile , " ");
fprintf(logfile , " %02X",(unsigned int)data[i]);
if( i==Size-1) //print the last spaces
{
for(j=0;j<15-i%16;j++)
{
fprintf(logfile , " "); //extra spaces
}
fprintf(logfile , " ");
for(j=i-i%16 ; j<=i ; j++)
{
if(data[j]>=32 && data[j]<=128)
{
fprintf(logfile , "%c",(unsigned char)data[j]);
}
else
{
fprintf(logfile , ".");
}
}
fprintf(logfile , "\n" );
}
}
}
The program requires superuser or root privileges to be able to sniff the packets.
Wireshark(previously ethereal) and tcpdump are examples of applications which use the libpcap library on linux to capture packet data.
