import logging
logging.getLogger("scapy.runtime").setLevel(logging.ERROR)
from scapy.all import *
from time import time, sleep

conf.verb = 0

dhcpserversinit = []
dhcpservers = []

init = 1

fam, hw = get_if_raw_hwaddr(conf.iface)

def dhcp_callback(pkt):

    if DHCP in pkt and pkt[DHCP].options[0][1] == 2:
    if init == 1:
        dhcpserversinit.append(pkt[IP].src)
    else:
        dhcpservers.append(pkt[IP].src)

dhcp_request = (
    Ether(dst='ff:ff:ff:ff:ff:ff') /
    IP(src='0.0.0.0', dst='255.255.255.255') /
    UDP(sport=68, dport=67) /
    BOOTP(chaddr=hw) /
    DHCP(options=[('message-type', 'discover'), 'end'])
)

sendp(dhcp_request)

sniff(prn=dhcp_callback, store=0, count=5)

init = 0

print "Servidores DHCP Encontrados:"
print "\n".join(dhcpserversinit)

while True:

    dhcp_request = (
        Ether(dst='ff:ff:ff:ff:ff:ff') /
        IP(src='0.0.0.0', dst='255.255.255.255') /
        UDP(sport=68, dport=67) /
        BOOTP(chaddr=hw) /
        DHCP(options=[('message-type', 'discover'), 'end'])
    )

    sendp(dhcp_request)

    sniff(prn=dhcp_callback, store=0, count=5)

    newdhcp = set(dhcpservers)
    alerts= newdhcp.difference(dhcpserversinit)

    if alerts:
        print "Nuevo servidor DHCP encontrado"
        print "\n".join(dhcpservers)

    dhcpserversinit = dhcpservers
    dhcpservers = []

    sleep(20)