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I have heard that we can create ip-packets by our own and send it to a network or a host. How this Can Be Done ?Please Explain step by step??

VijayPandey
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1 Answers1

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PCap library can be used not only to sniff packets, but also to construct and send packets.

In the field of computer network administration, pcap (packet capture) consists of an application programming interface (API) for capturing network traffic. Unix-like systems implement pcap in the libpcap library; Windows uses a port of libpcap known as WinPcap.

There is a good example:

The simplest way to send a packet is shown in the following code snippet. After opening an adapter, pcap_sendpacket() is called to send a hand-crafted packet. pcap_sendpacket() takes as arguments a buffer containing the data to send, the length of the buffer and the adapter that will send it. Notice that the buffer is sent to the net as is, without any manipulation. This means that the application has to create the correct protocol headers in order to send something meaningful.

Please note you have the full control. You can change Ethernet frame as well.

#include <stdlib.h>
#include <stdio.h>

#include <pcap.h>


void main(int argc, char **argv)
{
pcap_t *fp;
char errbuf[PCAP_ERRBUF_SIZE];
u_char packet[100];
int i;

    /* Check the validity of the command line */
    if (argc != 2)
    {
        printf("usage: %s interface (e.g. 'rpcap://eth0')", argv[0]);
        return;
    }

    /* Open the output device */
    if ( (fp= pcap_open(argv[1],            // name of the device
                        100,                // portion of the packet to capture (only the first 100 bytes)
                        PCAP_OPENFLAG_PROMISCUOUS,  // promiscuous mode
                        1000,               // read timeout
                        NULL,               // authentication on the remote machine
                        errbuf              // error buffer
                        ) ) == NULL)
    {
        fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n", argv[1]);
        return;
    }

    /* Supposing to be on ethernet, set mac destination to 1:1:1:1:1:1 */
    packet[0]=1;
    packet[1]=1;
    packet[2]=1;
    packet[3]=1;
    packet[4]=1;
    packet[5]=1;

    /* set mac source to 2:2:2:2:2:2 */
    packet[6]=2;
    packet[7]=2;
    packet[8]=2;
    packet[9]=2;
    packet[10]=2;
    packet[11]=2;

    /* Fill the rest of the packet */
    for(i=12;i<100;i++)
    {
        packet[i]=i%256;
    }

    /* Send down the packet */
    if (pcap_sendpacket(fp, packet, 100 /* size */) != 0)
    {
        fprintf(stderr,"\nError sending the packet: \n", pcap_geterr(fp));
        return;
    }

    return;
}

Update

There are several wrappers available:

Renat Gilmanov
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