ip_header_decode.py

import socket
import os
import struct
from ctypes import *

host = "{INPUT HOST}"

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

# Create a raw socket and bind it to the public interface
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 Windows, we'll need to send some ioctls to setup promiscuous mode
if os.name == "nt":
    sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
try:
    while True:
        # Read in a single packet. Create an IP header from the first 20 bytes of the buffer.
        raw_buffer = sniffer.recvfrom(65565)[0]
        ip_header = IP(raw_buffer[0:20])
        print(f"Protocol: {ip_header.protocol} {ip_header.src_address} -> {ip_header.dst_address}")
except KeyboardInterrupt:
    # If we're on Windows turn off promiscuous mode
    if os.name == "nt":
        sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)