Python的网络编程[4] -> DHCP 协议 -> DHCP 的 Python 实现，,DHCP实现 / D
Python的网络编程[4] -> DHCP 协议 -> DHCP 的 Python 实现，,DHCP实现 / D
DHCP实现 / DHCP Implement
目录
DHCP 服务器建立过程DHCP 报文加码实现过程下面介绍建立一个简单的DHCP服务器，主要用于对基本的DHCP请求进行响应，目前只提供一个IP为客户端使用，实现最基本的通信示例。理论内容可参考 DHCP 理论部分。
1 DHCP 服务器建立过程
首先是基本服务器的建立，这个服务器实现了最基本的对DISCOVER和REQUEST报文的响应，在验证时会对魔术字进行验证，此处未对BOOTP进行处理，验证通过后会对Options字段进行验证，此处利用生成器来对字段进行获取，最终处理完所有信息后结束。
1 import socket 2 import struct 3 import binascii 4 import logging 5 from threading import Thread 6 from dhcp_offer import Offer 7 8 logging.basicConfig(level=logging.DEBUG, format=‘[%(asctime)s] %(threadName)s: %(message)s‘) 9 10 class DHCPServer(): 11 """ 12 This class implements parts of RFC-2131 13 Only DHCPDISCOVER and DHCPREQUEST allowed 14 """ 15 def __init__(self, boot_file=None, server_ip=None, offer_ip=None, tftp_ip=None): 16 Thread.__init__(self) 17 self._port = 67 18 self._boot_file = boot_file 19 self._file_index = 0 20 self._offer_ip = offer_ip 21 self._tftp_ip = tftp_ip 22 self.server_ip = server_ip 23 24 @property 25 def server_ip(self): 26 return self._server_ip 27 28 @server_ip.setter 29 def server_ip(self, server_ip): 30 self._server_ip = server_ip 31 self.send_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) 32 self.send_socket.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, True) 33 self.send_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True) 34 self.send_socket.bind((self._server_ip, self._port)) 35 36 @property 37 def boot_file(self): 38 return self._boot_file 39 40 @boot_file.setter 41 def boot_file(self, boot_file): 42 if not isinstance(boot_file, list): 43 boot_file = [boot_file] 44 self._boot_file = boot_file 45 self._file_index = 0 46 47 @property 48 def offer_ip(self): 49 return self._offer_ip 50 51 @offer_ip.setter 52 def offer_ip(self, offer_ip): 53 self._offer_ip = offer_ip 54 55 def check_msg(self, m): 56 is_valid, msg_type, select_ip = False, None, None 57 if (m[0] == b‘\x01‘ and 58 m[1] == b‘\x01‘ and 59 m[2] == b‘\x06‘ and 60 m[3] == b‘\x00‘ and 61 m[10:12] == [b‘\x00‘, b‘\x00‘] and 62 m[12:16] == [b‘\x00‘, b‘\x00‘, b‘\x00‘, b‘\x00‘] and 63 m[16:20] == [b‘\x00‘, b‘\x00‘, b‘\x00‘, b‘\x00‘] and 64 m[20:24] == [b‘\x00‘, b‘\x00‘, b‘\x00‘, b‘\x00‘] and 65 m[236:240] == [b‘\x63‘, b‘\x82‘, b‘\x53‘, b‘\x63‘] 66 ): 67 logging.warning(‘Valid DHCP message‘) 68 # Valid DHCPDISCOVER 69 opt = (x for x in m[240:]) 70 while opt: 71 try: 72 func_code = next(opt) 73 if func_code == b‘\x00‘: 74 break 75 length = next(opt) 76 items = b‘‘ 77 for i in range(ord(length)): 78 items += next(opt) 79 except StopIteration: 80 break 81 else: 82 if func_code == b‘\x35‘ and length == b‘\x01‘: 83 if items == b‘\x01‘: 84 logging.warning(‘DHCP Discover‘) 85 msg_type = ‘DSCV‘ 86 is_valid = True 87 if items == b‘\x03‘: 88 logging.warning(‘DHCP Request‘) 89 msg_type = ‘RQST‘ 90 91 # Assure DHCP server selected 92 if func_code == b‘\x36‘ and msg_type == ‘RQST‘: 93 logging.warning(‘DHCP Server Identifier check‘) 94 select_ip = socket.inet_ntoa(items) 95 96 # Double check DHCP offer ip 97 if func_code == b‘\x32‘ and select_ip == self._server_ip: 98 offer_ip = socket.inet_ntoa(items) 99 if offer_ip == self._offer_ip:100 is_valid = True101 else:102 logging.warning(‘Offer ip double check failed‘)103 104 return is_valid, msg_type105 106 def serve_forever(self):107 108 self.recv_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)109 self.recv_socket.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, True)110 self.recv_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True)111 self.recv_socket.bind((‘‘, self._port))112 113 if self._boot_file:114 if self._file_index >= len(self._boot_file):115 self._file_index = 0116 117 def handle_msg(msg, addr):118 send_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)119 send_socket.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, True)120 send_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True)121 send_socket.bind((self._server_ip, self._port))122 m = list(struct.unpack(‘c‘*len(msg), msg))123 is_valid, msg_type = self.check_msg(m)124 if is_valid:125 logging.warning(‘Valid %s message, try to response‘ % msg_type)126 pass_sec = ord(m[8]) * 256 + ord(m[9])127 transaction_id = ‘‘.join([‘%02x‘ % ord(x) for x in m[4:8]])128 client_mac_id = ‘:‘.join([‘%02x‘ % ord(x) for x in m[28:34]])129 if msg_type:130 offer = Offer(transaction_id=transaction_id,131 client_ip_offer=self._offer_ip,132 server_ip=self._server_ip,133 client_mac_id=client_mac_id,134 file_path=self._boot_file,135 pass_sec=pass_sec,136 msg_type=msg_type,137 tftp_ip = self._tftp_ip)138 send_socket.sendto(offer.packet, (‘<broadcast>‘, 68))139 self._file_index += 1140 logging.warning(‘Respone done‘)141 else:142 logging.warning(‘Invalid message, discard...‘)143 send_socket.close()144 145 while True:146 logging.warning(‘Waiting discovery...‘)147 msg, addr = self.recv_socket.recvfrom(8192)148 logging.warning(‘Receive message from %s, port %s‘ % addr)149 handler = Thread(target=handle_msg, args=(msg, addr))150 handler.start()151 152 if __name__ == ‘__main__‘:153 dhcp = DHCPServer(server_ip=‘127.0.0.1‘, offer_ip=‘127.0.0.10‘)154 dhcp.serve_forever()
2 DHCP 报文加码实现过程
Note: 此处为做示例，对网关等信息都设置为固定值，匹配服务器ip。
1 import binascii 2 import struct 3 import socket 4 5 class Offer(): 6 def __init__(self, transaction_id, client_ip_offer, server_ip, client_mac_id, file_path, pass_sec, msg_type, tftp_ip=None, lease_time=172800): 7 SERVER_NAME = ‘‘ 8 self._server_ip = server_ip 9 self._offer_ip = client_ip_offer10 self._lease_time = lease_time11 if not tftp_ip:12 tftp_ip = server_ip13 self._tftp_ip = tftp_ip14 if not file_path:15 file_path = ‘‘16 pass_sec = struct.pack(‘!H‘, pass_sec)17 client_mac_id = binascii.unhexlify(client_mac_id.replace(‘:‘, ‘‘))18 transaction_id = binascii.unhexlify(transaction_id)19 20 self.packet = b‘‘21 self.packet += b‘\x02‘ # op22 self.packet += b‘\x01‘ # htype23 self.packet += b‘\x06‘ # hlen24 self.packet += b‘\x00‘ # hops25 self.packet += transaction_id26 self.packet += pass_sec # secs27 self.packet += b‘\x00\x00‘ # flags28 self.packet += b‘\x00\x00\x00\x00‘ # current client ip29 self.packet += socket.inet_aton(client_ip_offer) # offer ip30 self.packet += socket.inet_aton(server_ip) # server ip31 self.packet += b‘\x00\x00\x00\x00‘ # gateway ip32 self.packet += client_mac_id # client mac id33 self.packet += b‘\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00‘ # client mac id padding34 self.packet += SERVER_NAME.encode(‘utf-8‘)35 self.packet += b‘\x00‘*(64-len(SERVER_NAME))36 self.packet += file_path.encode(‘utf-8‘)37 self.packet += b‘\x00‘*(128-len(file_path))38 self.packet += self.optional(msg_type)39 40 def optional(self, msg_type):41 magic = b‘\x63\x82\x53\x63‘42 opt = b‘‘43 # Message type44 if msg_type == ‘DSCV‘:45 opt += self.encode_int(53, 1, 2)46 if msg_type == ‘RQST‘:47 opt += self.encode_int(53, 1, 5)48 # Server identifier49 opt += self.encode_ip(54, 4, self._server_ip)50 # Subnet mask51 opt += self.encode_ip(1, 4, ‘255.255.255.0‘)52 # Router53 opt += self.encode_ip(3, 4, ‘127.0.0.1‘)54 # DNS server55 opt += self.encode_ip(6, 4, ‘127.0.0.1‘)56 # NetBios server57 opt += self.encode_ip(44, 4, ‘127.0.0.1‘)58 # IP address lease time59 opt += self.encode_int(51, 4, self._lease_time)60 # Extend lease time T161 opt += self.encode_int(58, 4, int(self._lease_time*0.5))62 # Extend lease time T263 opt += self.encode_int(59, 4, int(self._lease_time*0.8))64 # Log server65 opt += self.encode_ip(7, 4, ‘127.0.0.1‘)66 # TFTP server name67 opt += bytes([66, 11]) + self._tftp_ip.encode()68 # Tail69 # TODO: find out why a b‘\xff‘ for end70 opt += b‘\xff‘71 return magic+opt72 73 def encode_int(self, func, length, item):74 m = {1: ‘!B‘, 2: ‘!H‘, 4: ‘!I‘}75 s = b‘‘76 s += (bytes([func, length]) + struct.pack(m[length], item))77 return s78 79 def encode_ip(self, func, length, item):80 s = b‘‘81 s += bytes([func, length])82 s += socket.inet_aton(item)83 return s相关阅读
1. DHCP 理论
2. 生成器
Python的网络编程[4] -> DHCP 协议 -> DHCP 的 Python 实现
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