[New-bugs-announce] [issue35734] ipaddress's _BaseV4._is_valid_netmask fails to detect invalid netmask like 255.254.128.0

[ulin]

New submission from ulin <linlin152 at foxmail.com>:

valid netmask like 255.0.0.0 255.128.0.0, but 255.254.128.0 is not valid, but ipaddress._BaseV4._is_valid_netmask fails to detect the latter.

Tested in Python 3.6.7, as the code stays the same, affects all after Python 3.6.7.

----------
components: Library (Lib)
files: test_ipaddress.py
messages: 333581
nosy: ulindog
priority: normal
severity: normal
status: open
title: ipaddress's _BaseV4._is_valid_netmask fails to  detect invalid netmask like 255.254.128.0
type: behavior
versions: Python 3.8
Added file: https://bugs.python.org/file48047/test_ipaddress.py

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35734>
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