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tutorial_1.py
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134 lines (107 loc) · 4.78 KB
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import socket
BIG_ENDIAN = 'big'
LITTLE_ENDIAN = 'little'
ETH_P_ALL = 0x3
ETH_P_IP = 0x0800
ETH_P_ARP = 0x0806
ETH_P_RARP = 0x8035
ETH_P_IPV6 = 0x086dd
ETH_TYPE_MAP = {
ETH_P_IP: 'IP',
ETH_P_ARP: 'ARP',
ETH_P_RARP: 'RARP',
ETH_P_IPV6: 'IPv6'
}
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
class MACAddress:
def __init__(self, addr: int):
self.addr = addr
def __str__(self):
return ':'.join('{:02x}'.format(a) for a in self.addr.to_bytes(6, BIG_ENDIAN))
def __repr__(self):
return self.__str__()
class EthernetHeader:
def __init__(self, dst_mac, src_mac):
self.dst_mac = dst_mac
self.src_mac = src_mac
def describe(self):
return {
'src_mac': MACAddress(self.src_mac),
'dst_mac': MACAddress(self.dst_mac)
}
class EthernetIIHeader(EthernetHeader):
def __init__(self, dst_mac, src_mac):
super().__init__(dst_mac, src_mac)
self.eth_type = 0
def describe(self):
dct = super().describe()
dct['eth_type'] = self._describe_eth_type(self.eth_type)
return dct
@staticmethod
def _describe_eth_type(eth_type):
if eth_type in ETH_TYPE_MAP:
return ETH_TYPE_MAP[eth_type]
return 'Unknown protocol {}'.format(eth_type)
class Ethernet802_3Header(EthernetHeader):
def __init__(self, dst_mac, src_mac):
super().__init__(dst_mac, src_mac)
self.length = 0
self.llc = 0
self.snap = 0
def describe(self):
dct = super().describe()
dct['length'] = self.length
dct['llc'] = self.llc
dct['snap'] = self.snap
return dct
def unpack(packet):
dst_mac = int.from_bytes(packet[:6], BIG_ENDIAN)
src_mac = int.from_bytes(packet[6:12], BIG_ENDIAN)
if dst_mac == 0 or src_mac == 0:
print(packet)
type_or_length = int.from_bytes(packet[12:14], BIG_ENDIAN)
if type_or_length <= 1500:
"""
IEEE 802.3 帧长度字段值小于等于1500 (0x05DC)
IEEE 802.3帧格式类似于Ethernet_II帧，只是Ethernet_II帧的Type域被802.3帧的Length域取代，并且占用了Data字段的8个字节作为LLC和SNAP字段。
Length字段定义了Data字段包含的字节数。
逻辑链路控制LLC（Logical Link Control）由目的服务访问点DSAP（Destination Service Access Point）、源服务访问点SSAP（Source Service Access Point）和Control字段组成。
SNAP（Sub-network Access Protocol）由机构代码（Org Code）和类型（Type）字段组成。Org code三个字节都为0。Type字段的含义与Ethernet_II帧中的Type字段相同。IEEE802.3帧根据DSAP和SSAP字段的取值又可分为以下几类：
当DSAP和SSAP都取特定值0xff时，802.3帧就变成了Netware-ETHERNET帧，用来承载NetWare类型的数据。
当DSAP和SSAP都取特定值0xaa时，802.3帧就变成了ETHERNET_SNAP帧。ETHERNET_SNAP帧可以用于传输多种协议。
DSAP和SSAP其他的取值均为纯IEEE802.3帧。
"""
hdr = Ethernet802_3Header(dst_mac, src_mac)
hdr.length = type_or_length
hdr.llc = int.from_bytes(packet[14:17], BIG_ENDIAN)
hdr.snap = int.from_bytes(packet[17:22], BIG_ENDIAN)
return hdr, packet[22:]
elif type_or_length >= 1536:
"""
Ethernet_II 帧类型值大于等于1536 (0x0600)
以太网数据帧的长度在64-1518字节之间
Ethernet_II的帧中各字段说明如下：
DMAC（Destination MAC）是目的MAC地址。DMAC字段长度为6个字节，标识帧的接收者。
SMAC（Source MAC）是源MAC地址。SMAC字段长度为6个字节，标识帧的发送者。
类型字段（Type）用于标识数据字段中包含的高层协议，该字段长度为2个字节。类型字段取值为0x0800的帧代表IP协议帧；类型字段取值为0806的帧代表ARP协议帧。
数据字段(Data)是网络层数据，最小长度必须为46字节以保证帧长至少为64字节，数据字段的最大长度为1500字节。
循环冗余校验字段（FCS）提供了一种错误检测机制。该字段长度为4个字节。
"""
hdr = EthernetIIHeader(dst_mac, src_mac)
hdr.eth_type = type_or_length
return hdr, packet[14:]
else:
raise ValueError(type_or_length)
def main():
raw_sock = socket.socket(socket.PF_PACKET, socket.SOCK_RAW, socket.htons(ETH_P_ALL))
while True:
try:
packet, packet_info = raw_sock.recvfrom(1800)
eth_header, payload = unpack(packet)
print(eth_header.describe(), payload)
except KeyboardInterrupt:
break
except ValueError as e:
print('unpack failed', e)
if __name__ == '__main__':
main()