为什么此代码在某些情况下无法识别 IP 的类别？

Question

我编写了以下 Python 代码，用于对 IP 是否有效进行分类，如果有效则归类到它所属的类以及是否为私有：

from ipaddress import IPv4Address, IPv4Network, ip_address
import sys

try:
    ip = ip_address(sys.argv[1])
    print(f"{ip} is a correct IP{ip.version} address.")
    if ip_address(ip).is_private:
            print("It is a private IP.")
    classA = IPv4Network(("10.0.0.0", "255.0.0.0")) 
    classB = IPv4Network(("172.16.0.0", "255.240.0.0"))
    classC = IPv4Network(("192.168.0.0", "255.255.0.0")) 
    if ip in classA:
        print(f"{ip} is a correct class A IP{ip.version} address.")
        if ip_address(ip).is_private:
            print("It is a private IP.")
    elif ip in classB:
        print(f"{ip} is a correct class B IP{ip.version} address.")
        if ip_address(ip).is_private:
            print("It is a private IP.")
    elif ip in classC:
        print(f"{ip} is a correct class C IP{ip.version} address.") 
        if ip_address(ip).is_private:
            print("It is a private IP.")
except ValueError:
    print(f'address/netmask is invalid: {sys.argv[1]}')
except:
    print(f'Usage : {sys.argv[0]}  ip')

我假设that the range of A 类从1.0.0.0 到127.255.255.255，B 类从128.0.0.0 到191.255.255.255，C 类从192.0.0.0 到223.255.255.255。 当给定141.68.27.102 时，它不会 将类归类为 B（尽管the answer to this cisco lab does），为什么会这样？ 当给定192.12.13.14时，它不会 将类归类为 C（虽然 the answer to this cisco lab does），为什么会这样？

Answer 1

简短的回答是“因为这些 IP 不属于您定义的类”。

您的程序的这种稍微简化的返工首先打印出类，因此您可以看到您是如何定义它们的......以及为什么它们似乎不正确匹配。

from ipaddress import IPv4Network, ip_address

classes = {
    "A": IPv4Network(("10.0.0.0", "255.0.0.0")),
    "B": IPv4Network(("172.16.0.0", "255.240.0.0")),
    "C": IPv4Network(("192.168.0.0", "255.255.0.0")),
}


def describe_ip(ip_str):
    ip = ip_address(ip_str)
    for class_name, network in classes.items():
        if ip in network:
            print(f"{ip} is a correct class {class_name} IP{ip.version} address.")
            break
    else:
        print(f"{ip} does not belong in any of the classes defined.")


print(classes)
describe_ip("172.32.255.255")
describe_ip("141.68.27.102")
describe_ip("192.12.13.14")
describe_ip("172.16.255.255")

输出类似于（最后一行证明 172.16. 地址确实符合您的 B 类定义）。

{'A': IPv4Network('10.0.0.0/8'), 'B': IPv4Network('172.16.0.0/12'), 'C': IPv4Network('192.168.0.0/16')}
172.32.255.255 does not belong in any of the classes defined.
141.68.27.102 does not belong in any of the classes defined.
192.12.13.14 does not belong in any of the classes defined.
172.16.255.255 is a correct class B IP4 address.