如何阻止来自 dnsmasq 的 DHCPACK？

Question

我正在使用包含 Rpi 和 esp8266 的网络。我试图了解 DHCP 消息握手。从测试中，我了解到，如果没有收到 DHCPOFFER，esp8266 将以 2、4、8、16 秒的间隔启动 DHCPDISCOVER 消息。本次测试是通过屏蔽dnsmasq.conf文件中的特定esp8266进行的。

现在我要测试一下，如果esp8266收不到DHCPACK怎么办。他们会重新发出命令 DHCPREQUEST 吗？或 DHCPDISCOVER？

但是 rpi(dnsmasq) 中的 DHCP 服务器运行没有阻止 DHCPACK 信号的规定。那么我该如何进行测试呢？

我尝试使用 python 模拟 DHCP 服务器，但没有任何效果。

Answer 1

无论如何！我得到了答案。这可能对其他人有用，这就是我分享它的原因。

我使用 python 制作了 DHCP 服务器，我能够控制服务器发送的 DHCP 数据包。代码如下。

import os
os.sys.path.append('/usr/local/lib/python3.6/site-packages')
# DHCP Discover Package

from scapy.all import *
import binascii
import _thread
import time


import logging
from logging.handlers import RotatingFileHandler
log_formatter = logging.Formatter('%(asctime)s : %(message)s')


logFile = '/home/pi/simulation/dhcp.log'

rotate_handler = RotatingFileHandler(logFile, mode='a', maxBytes=1024*1024, 
                                 backupCount=1)
rotate_handler.setFormatter(log_formatter)

Logging = logging.getLogger()
Logging.setLevel(logging.DEBUG)
Logging.addHandler(rotate_handler)


Version = "1.0.0"
Logging.debug("DHCP server "+ Version)

interface="eth1"

server_mac="70:88:6b:82:7d:30"
client_ip="192.168.42.25"
server_ip="192.168.42.1"
subnet_mask="255.255.255.0"
lease_time=86400
renewal_time = int(lease_time/2)
rebind_time = int(float(lease_time)*.875)

block_ack=True
block_offer=True
# Define a function for threads
def sent_discover( threadName, delay):
    while(1):
        xid_random = random.randint(1, 900000000)
        mac_random = str(RandMAC())
        print(mac_random)
        client_mac_id = binascii.unhexlify(mac_random.replace(':', ''))
        dhcp_discover = Ether(src=mac_random, 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=client_mac_id, xid=xid_random) / DHCP(options=[("message-type", "discover"), "end"])
        sendp(dhcp_discover, iface=interface)
        time.sleep(delay)
def sniff_discover(threadName, delay):
    print("sniff called")
    def detect_dhcp(pkt):
        #print("Detecting..")
        if DHCP in pkt:
           
            ##Below DHCP server
            if pkt[DHCP].options[0][1] == 1:
                Logging.debug("DHCPDISCOVER(%s) %s"%(interface, pkt[Ether].src))
                Ether_Request = Ether(src=server_mac, dst=pkt[Ether].src)
                IP_Request = IP(src=server_ip, dst=client_ip)
                UDP_Request = UDP(sport=67, dport=68)
                BOOTP_Request = BOOTP(op=2,yiaddr=client_ip,siaddr=server_ip,chaddr=pkt[BOOTP].chaddr, xid=pkt[BOOTP].xid)
                DHCP_Request = DHCP(options=[("message-type", 'offer'), ("server_id", server_ip),
                                             ("lease_time", lease_time), ("renewal_time", renewal_time),
                                             ("rebinding_time", rebind_time), ("subnet_mask", subnet_mask),
                                             ("broadcast_address", "192.168.42.255"), ("router", "192.168.42.1"),
                                             ("name_server", "192.168.42.1"), ("domain", "pyClar"), "end"])
                Offer = Ether_Request / IP_Request / UDP_Request / BOOTP_Request / DHCP_Request
                if not block_offer:
                    sendp(Offer, iface=interface)
                    Logging.debug("DHCPOFFER(%s) %s %s"%(interface, client_ip, pkt[Ether].src))
                    print("DHCPOFFER sent")
                else:
                    print("DHCPOFFER ignored")
            if pkt[DHCP].options[0][1] == 3:
                Logging.debug("DHCPREQUEST(%s) %s %s"%(interface, client_ip, pkt[Ether].src))
                Ether_Request = Ether(src=server_mac, dst=pkt[Ether].src)
                IP_Request = IP(src=server_ip, dst=client_ip)
                UDP_Request = UDP(sport=67, dport=68)
                BOOTP_Request = BOOTP(op=2,yiaddr=client_ip,siaddr=server_ip,chaddr=pkt[BOOTP].chaddr, xid=pkt[BOOTP].xid)
                DHCP_Request = DHCP(options=[("message-type", 'ack'), ("server_id", server_ip),
                                             ("lease_time", lease_time), ("renewal_time", renewal_time),
                                             ("rebinding_time", rebind_time), ("subnet_mask", subnet_mask),
                                             ("broadcast_address", "192.168.42.255"), ("router", "192.168.42.1"),
                                             ("name_server", "192.168.42.1"), ("domain", "pyClar"), "end"])
                Ack = Ether_Request / IP_Request / UDP_Request / BOOTP_Request / DHCP_Request
                if not block_ack:
                    sendp(Ack, iface=interface)
                    Logging.debug("DHCPACK(%s) %s %s"%(interface, client_ip, pkt[Ether].src))
                    print("DHCPACK sent")
                else:
                    print("DHCPACK is ignored")
                
                
    sniff(filter="port 67", iface=interface, prn=detect_dhcp)
try:
    _thread.start_new_thread( sniff_discover, ("Thread-1", 0, ) )
    #_thread.start_new_thread( sent_discover, ("Thread-2", 10, ) )
except:
    print ("Error: Unable to start thread")
while 1:
    pass

如何阻止来自 dnsmasq 的 DHCPACK？

How to block DHCPACK from dnsmasq?

networking

raspberry-pi3

esp8266

dhcp