Question

我在运行Wireshark的远程PLC上运行下面的代码示例。为什么我只得到查询（我也应该得到回复）？似乎PLC发送响应，因为Scapy的输出说Received 1 packets, got 1 answers, remaining 0 packets。

为什么会发生这种情况？

我还使用Scapy的sniff（）函数执行了嗅探，但结果相同（仅获取查询）。

#! /usr/bin/env python

import logging
logging.getLogger("scapy").setLevel(1)

from scapy import *
from modLib import *

# IP for all transmissions
ip = IP(dst="192.168.10.131")

# Sets up the session with a TCP three-way handshake
# Send the syn, receive the syn/ack
tcp = TCP( flags = 'S', window = 65535, sport = RandShort(), dport = 502, options = [('MSS', 1360 ), ('NOP', 1), ('NOP', 1), ('SAckOK', '')])
synAck = sr1 ( ip / tcp )

# Send the ack
tcp.flags = 'A'
tcp.sport = synAck[TCP].dport
tcp.seq = synAck[TCP].ack
tcp.ack = synAck[TCP].seq + 1
tcp.options = ''
send( ip / tcp )

# Creates and sends the Modbus Read Holding Registers command packet
# Send the ack/push i.e. the request, receive the data i.e. the response
tcp.flags = 'AP'
adu = ModbusADU()
pdu = ModbusPDU03()
adu = adu / pdu
tcp = tcp / adu
data = sr1(( ip / tcp ), timeout = 2)
data.show()

# Acknowledges the response
# Ack the data response
# TODO: note, the 17 below should be replaced with a read packet length method...
tcp.flags = 'A'
tcp.seq = data[TCP].ack
tcp.ack = data[TCP] + 17
tcp.payload = ''
finAck = sr1( ip / tcp )

Answer 1

首先，您的代码中存在错误（原始版本http://www.digitalbond.com/scadapedia/security-controls/scapy-modbus-extensions/中存在该错误），您需要在其中添加.seq：tcp.ack = data[TCP].seq + 17。

正如评论中所说，你可以写tcp.ack = data[TCP].seq + len(data[TCP].payload)。

无论如何，对于你尝试做的事情来说，TCP栈的工作通常是没用的。

我会做那样的事情：

from scapy import *
from modLib import *
import socket

sock = socket.socket()
sock.connect(("192.168.10.131", 502))
s = StreamSocket(sock, basecls=ModbusADU)

ans, unans = s.sr(ModbusADU()/ModbusPDU03())
ans.show()

这会更好吗？

Wireshark没有获得Scapy Modbus响应

1 个答案: