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Wed Jun 3 14:49:18 CEST 2009 · https://mail.python.org/pipermail/python-dev/2009-June/089857.html

Paul Moore wrote:

> Note 1 - by the way, I use this form because I don't understand how
> the /24 notation works. I can get the subnet mask from ipconfig, so I
> use that.

<OT>

It's just a shorthand way of writing IPv4 net masks based on their
binary form:

/8 = 8 ones followed by 24 zeroes = 255.0.0.0
/16 = 16 ones followed by 16 zeroes = 255.255.0.0
/24 = 24 ones followed by 8 zeroes = 255.255.255.0
/30 = 30 ones followed by 2 zeroes = 255.255.255.252
/32 = 32 ones followed by no zeroes = 255.255.255.255

It's particularly convenient when you're dividing subnets up into chunks
that don't align with a byte boundary in the IPv4 address (e.g. /27 can
easily be recognised as giving a subnet containing 2**5 = 32 hosts, but
the subnet size is significantly less obvious when written using the
equivalent 255.255.255.224 netmask).

</OT>

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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[Python-Dev] Issues with Py3.1's new ipaddr