Tiny PXE boot server for specific mac address w/ no side effects. (No DHCPNAKs to other hosts.)

dhcpd.py

#!/usr/bin/env python

import argparse
import struct
import logging

logging.getLogger('scapy').setLevel(logging.WARNING)
from scapy.all import *

def packMAC(s):
	return ''.join([struct.pack('!B', int(x, 16)) for x in s.split(':')])

def pxeboot(iface, mac, ip, tftp_server=None, file=None, netmask=None, gateway=None):
	server_ip = get_if_addr(iface)
	server_mac = get_if_hwaddr(iface)
	client_ip = ip
	client_mac = mac

	if tftp_server is None:
		tftp_server = server_ip
	if file is None:
		file = 'pxeboot'

	def handle_pkt(pkt):
		# Are we a DHCP packet?
		try:
			pkt[DHCP]
		except:
			return

		# Ignore unless from the MAC we care about.
		if pkt[Ether].src != client_mac:
			print pkt[Ether].src+': wrong MAC: Ignoring request.'
			return

		if pkt[DHCP].options[0][1] == 1: # DHCP Discover
			print pkt[Ether].src+': got DHCP Discover.'
			reply_type = 'offer'
		elif pkt[DHCP].options[0][1] == 3: # DHCP Request
			print pkt[Ether].src+': got DHCP Request.'
			reply_type = 'ack'
		else:
			print pkt[Ether].src+': unknown DHCP option: Ignoring request.'
			return # Ignore all others

		p = Ether(src=server_mac, dst=pkt[Ether].src)
		p /= IP(src=server_ip, dst=client_ip)
		p /= UDP(sport=67, dport=68)
		p /= BOOTP(
			op=2,
			yiaddr=client_ip,
			siaddr=tftp_server,
			chaddr=packMAC(pkt[Ether].src),
			file=file,
			xid=pkt[BOOTP].xid)
		if gateway is not None:
			p[BOOTP].giaddr=gateway
		p /= DHCP(options=[('message-type', reply_type)])
		if netmask is not None:
			p /= DHCP(options=[('subnet_mask', netmask)])
		p /= DHCP(options=[('server_id', server_ip), 'end'])
		sendp(p, verbose=False)

		print reply_type+' sent'

	sniff(filter='arp or (udp and (port 67 or 68))', prn=handle_pkt, store=0)

parser = argparse.ArgumentParser(description='Whitelisting PXE boot server.')
parser.add_argument('interface')
parser.add_argument('mac')
parser.add_argument('ip')
parser.add_argument('-t', '--tftp-server', default=None)
parser.add_argument('-f', '--file', default=None)
parser.add_argument('-n', '--netmask', default=None)
parser.add_argument('-g', '--gateway', default=None)
args = parser.parse_args()

conf.checkIPaddr = False
conf.iface = args.interface

# Sniff DHCP requests
pxeboot(iface=args.interface, mac=args.mac, ip=args.ip, tftp_server=args.tftp_server, file=args.file, netmask=args.netmask, gateway=args.gateway)