无法在Python中建立Dns封包 [英] Having trouble building a Dns Packet in Python

问题描述

我正在尝试构建一个dns数据包以通过套接字发送.我不想使用任何库，因为我想直接访问发送它的套接字变量.每当我发送DNS数据包时，wireshark都会说它格式错误.我到底在做错什么?

I'm trying to build a dns packet to send over a socket. I don't want to use any libraries because I want direct access to the socket variable that sends it. Whenever I send the DNS packet, wireshark says that it's malformed. What exactly am I doing wrong?

Dns数据包本身有一些错误: 它说它有256个问题，没有课程，没有类型

Some things that are wrong with the Dns packet itself: It says it has 256 questions, no class and no type

  class DnsPacketBuilder:

def __init__(self):
    pass

def build_packet(self, url):
    packet = struct.pack("H", 12049)  # Query Ids (Just 1 for now)
    packet += struct.pack("H", 256)  # Flags
    packet += struct.pack("H", 1)  # Questions
    packet += struct.pack("H", 0)  # Answers
    packet += struct.pack("H", 0)  # Authorities
    packet += struct.pack("H", 0)  # Additional
    split_url = url.split(".")
    for part in split_url:
        packet += struct.pack("B", len(part))
        for byte in bytes(part):
            packet += struct.pack("c", byte)
    packet += struct.pack("B", 0)  # End of String
    packet += struct.pack("H", 1)  # Query Type
    packet += struct.pack("H", 1)  # Query Class
    return packet

# Sending the packet
builder = DnsPacketBuilder()
packet = builder.build_packet("www.northeastern.edu")
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(('', 8888))
sock.settimeout(2)
sock.sendto(bytes(packet), ("208.67.222.222", 53))
print("Packet Sent")
data, addr = sock.recvfrom(1024)
print("Response: " + data)
sock.close()

推荐答案

您的系统本机使用"little endian"字节顺序.

Your system is using "little endian" byte order natively.

您需要使用">H"

You need to reverse the byte order of the 16-bit fields into "big endian" (aka "network order") using the ">H" format string in struct.pack().

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