Decoding the IP Layer by using Python

Decoding the IP Layer by using Python

import socket
import os
import struct
from ctypes import *

# host to listen on
host = “192.168.0.187”

# our IP header
class IP(Structure):
 
    _fields_ = [
    (“ihl”, c_ubyte, 4),
    (“version”, c_ubyte, 4),
    (“tos”, c_ubyte),
    (“len”, c_ushort),
    (“id”, c_ushort),
    (“offset”, c_ushort),
    (“ttl”, c_ubyte),
    (“protocol_num”, c_ubyte),
    (“sum”, c_ushort),
    (“src”, c_ulong),
    (“dst”, c_ulong)
    ]

    def __new__(self, socket_buffer=None):
        return self.from_buffer_copy(socket_buffer)


    def __init__(self, socket_buffer=None):
        # map protocol constants to their names
        self.protocol_map = {1:”ICMP”, 6:”TCP”, 17:”UDP”}

        # human readable IP addresses
        self.src_address = socket.inet_ntoa(struct.pack(“<L”,self.src))
        self.dst_address = socket.inet_ntoa(struct.pack(“<L”,self.dst))

        # human readable protocol
        try:
            self.protocol = self.protocol_map[self.protocol_num]
        except:
            self.protocol = str(self.protocol_num)


        # this should look familiar from the previous example
        if os.name == “nt”:
            socket_protocol = socket.IPPROTO_IP
        else:
            socket_protocol = socket.IPPROTO_ICMP
            sniffer = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket_protocol)
            sniffer.bind((host, 0))
            sniffer.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)

        if os.name == “nt”:
            sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)

        try:
            while True:

                # read in a packet
                raw_buffer = sniffer.recvfrom(65565)[0]

                # create an IP header from the first 20 bytes of the buffer
                ip_header = IP(raw_buffer[0:20])

                # print out the protocol that was detected and the hosts
                print “Protocol: %s %s -> %s” % (ip_header.protocol, ip_header.src_
                address, ip_header.dst_address)

        # handle CTRL-C
        except KeyboardInterrupt:

            # if we’re using Windows, turn off promiscuous mode
            if os.name == “nt”:
            sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)

https://codingsec.net/2016/05/decoding-ip-layer-python/