
An introduction to the ipaddress module
***************************************

author:
   Peter Moody

author:
   Nick Coghlan


Overview
^^^^^^^^

This document aims to provide a gentle introduction to the
``ipaddress`` module. It is aimed primarily at users that aren't
already familiar with IP networking terminology, but may also be
useful to network engineers wanting an overview of how ``ipaddress``
represents IP network addressing concepts.


Creating Address/Network/Interface objects
==========================================

Since ``ipaddress`` is a module for inspecting and manipulating IP
addresses, the first thing you'll want to do is create some objects.
You can use ``ipaddress`` to create objects from strings and integers.


A Note on IP Versions
---------------------

For readers that aren't particularly familiar with IP addressing, it's
important to know that the Internet Protocol is currently in the
process of moving from version 4 of the protocol to version 6. This
transition is occurring largely because version 4 of the protocol
doesn't provide enough addresses to handle the needs of the whole
world, especially given the increasing number of devices with direct
connections to the internet.

Explaining the details of the differences between the two versions of
the protocol is beyond the scope of this introduction, but readers
need to at least be aware that these two versions exist, and it will
sometimes be necessary to force the use of one version or the other.


IP Host Addresses
-----------------

Addresses, often referred to as "host addresses" are the most basic
unit when working with IP addressing. The simplest way to create
addresses is to use the ``ipaddress.ip_address()`` factory function,
which automatically determines whether to create an IPv4 or IPv6
address based on the passed in value:

   >>> ipaddress.ip_address('192.0.2.1')
   IPv4Address('192.0.2.1')
   >>> ipaddress.ip_address('2001:DB8::1')
   IPv6Address('2001:db8::1')

Addresses can also be created directly from integers. Values that will
fit within 32 bits are assumed to be IPv4 addresses:

   >>> ipaddress.ip_address(3221225985)
   IPv4Address('192.0.2.1')
   >>> ipaddress.ip_address(42540766411282592856903984951653826561)
   IPv6Address('2001:db8::1')

To force the use of IPv4 or IPv6 addresses, the relevant classes can
be invoked directly. This is particularly useful to force creation of
IPv6 addresses for small integers:

   >>> ipaddress.ip_address(1)
   IPv4Address('0.0.0.1')
   >>> ipaddress.IPv4Address(1)
   IPv4Address('0.0.0.1')
   >>> ipaddress.IPv6Address(1)
   IPv6Address('::1')


Defining Networks
-----------------

Host addresses are usually grouped together into IP networks, so
``ipaddress`` provides a way to create, inspect and manipulate network
definitions. IP network objects are constructed from strings that
define the range of host addresses that are part of that network. The
simplest form for that information is a "network address/network
prefix" pair, where the prefix defines the number of leading bits that
are compared to determine whether or not an address is part of the
network and the network address defines the expected value of those
bits.

As for addresses, a factory function is provided that determines the
correct IP version automatically:

   >>> ipaddress.ip_network('192.0.2.0/24')
   IPv4Network('192.0.2.0/24')
   >>> ipaddress.ip_network('2001:db8::0/96')
   IPv6Network('2001:db8::/96')

Network objects cannot have any host bits set.  The practical effect
of this is that ``192.0.2.1/24`` does not describe a network.  Such
definitions are referred to as interface objects since the ip-
on-a-network notation is commonly used to describe network interfaces
of a computer on a given network and are described further in the next
section.

By default, attempting to create a network object with host bits set
will result in ``ValueError`` being raised. To request that the
additional bits instead be coerced to zero, the flag ``strict=False``
can be passed to the constructor:

   >>> ipaddress.ip_network('192.0.2.1/24')
   Traceback (most recent call last):
      ...
   ValueError: 192.0.2.1/24 has host bits set
   >>> ipaddress.ip_network('192.0.2.1/24', strict=False)
   IPv4Network('192.0.2.0/24')

While the string form offers significantly more flexibility, networks
can also be defined with integers, just like host addresses. In this
case, the network is considered to contain only the single address
identified by the integer, so the network prefix includes the entire
network address:

   >>> ipaddress.ip_network(3221225984)
   IPv4Network('192.0.2.0/32')
   >>> ipaddress.ip_network(42540766411282592856903984951653826560)
   IPv6Network('2001:db8::/128')

As with addresses, creation of a particular kind of network can be
forced by calling the class constructor directly instead of using the
factory function.


Host Interfaces
---------------

As mentioned just above, if you need to describe an address on a
particular network, neither the address nor the network classes are
sufficient. Notation like ``192.0.2.1/24`` is commonly used by network
engineers and the people who write tools for firewalls and routers as
shorthand for "the host ``192.0.2.1`` on the network
``192.0.2.0/24``", Accordingly, ``ipaddress`` provides a set of hybrid
classes that associate an address with a particular network. The
interface for creation is identical to that for defining network
objects, except that the address portion isn't constrained to being a
network address.

>>> ipaddress.ip_interface('192.0.2.1/24')
IPv4Interface('192.0.2.1/24')
>>> ipaddress.ip_interface('2001:db8::1/96')
IPv6Interface('2001:db8::1/96')

Integer inputs are accepted (as with networks), and use of a
particular IP version can be forced by calling the relevant
constructor directly.


Inspecting Address/Network/Interface Objects
============================================

You've gone to the trouble of creating an
IPv(4|6)(Address|Network|Interface) object, so you probably want to
get information about it.  ``ipaddress`` tries to make doing this easy
and intuitive.

Extracting the IP version:

   >>> addr4 = ipaddress.ip_address('192.0.2.1')
   >>> addr6 = ipaddress.ip_address('2001:db8::1')
   >>> addr6.version
   6
   >>> addr4.version
   4

Obtaining the network from an interface:

   >>> host4 = ipaddress.ip_interface('192.0.2.1/24')
   >>> host4.network
   IPv4Network('192.0.2.0/24')
   >>> host6 = ipaddress.ip_interface('2001:db8::1/96')
   >>> host6.network
   IPv6Network('2001:db8::/96')

Finding out how many individual addresses are in a network:

   >>> net4 = ipaddress.ip_network('192.0.2.0/24')
   >>> net4.num_addresses
   256
   >>> net6 = ipaddress.ip_network('2001:db8::0/96')
   >>> net6.num_addresses
   4294967296

Iterating through the "usable" addresses on a network:

   >>> net4 = ipaddress.ip_network('192.0.2.0/24')
   >>> for x in net4.hosts():
   ...     print(x)  # doctest: +ELLIPSIS
   192.0.2.1
   192.0.2.2
   192.0.2.3
   192.0.2.4
   ...
   192.0.2.252
   192.0.2.253
   192.0.2.254

Obtaining the netmask (i.e. set bits corresponding to the network
prefix) or the hostmask (any bits that are not part of the netmask):

>>> net4 = ipaddress.ip_network('192.0.2.0/24')
>>> net4.netmask
IPv4Address('255.255.255.0')
>>> net4.hostmask
IPv4Address('0.0.0.255')
>>> net6 = ipaddress.ip_network('2001:db8::0/96')
>>> net6.netmask
IPv6Address('ffff:ffff:ffff:ffff:ffff:ffff::')
>>> net6.hostmask
IPv6Address('::ffff:ffff')

Exploding or compressing the address:

   >>> addr6.exploded
   '2001:0db8:0000:0000:0000:0000:0000:0001'
   >>> addr6.compressed
   '2001:db8::1'
   >>> net6.exploded
   '2001:0db8:0000:0000:0000:0000:0000:0000/96'
   >>> net6.compressed
   '2001:db8::/96'

While IPv4 doesn't support explosion or compression, the associated
objects still provide the relevant properties so that version neutral
code can easily ensure the most concise or most verbose form is used
for IPv6 addresses while still correctly handling IPv4 addresses.


Networks as lists of Addresses
==============================

It's sometimes useful to treat networks as lists.  This means it is
possible to index them like this:

   >>> net4[1]
   IPv4Address('192.0.2.1')
   >>> net4[-1]
   IPv4Address('192.0.2.255')
   >>> net6[1]
   IPv6Address('2001:db8::1')
   >>> net6[-1]
   IPv6Address('2001:db8::ffff:ffff')

It also means that network objects lend themselves to using the list
membership test syntax like this:

   if address in network:
       # do something

Containment testing is done efficiently based on the network prefix:

   >>> addr4 = ipaddress.ip_address('192.0.2.1')
   >>> addr4 in ipaddress.ip_network('192.0.2.0/24')
   True
   >>> addr4 in ipaddress.ip_network('192.0.3.0/24')
   False


Comparisons
===========

``ipaddress`` provides some simple, hopefully intuitive ways to
compare objects, where it makes sense:

   >>> ipaddress.ip_address('192.0.2.1') < ipaddress.ip_address('192.0.2.2')
   True

A ``TypeError`` exception is raised if you try to compare objects of
different versions or different types.


Using IP Addresses with other modules
=====================================

Other modules that use IP addresses (such as ``socket``) usually won't
accept objects from this module directly. Instead, they must be
coerced to an integer or string that the other module will accept:

   >>> addr4 = ipaddress.ip_address('192.0.2.1')
   >>> str(addr4)
   '192.0.2.1'
   >>> int(addr4)
   3221225985


Getting more detail when instance creation fails
================================================

When creating address/network/interface objects using the version-
agnostic factory functions, any errors will be reported as
``ValueError`` with a generic error message that simply says the
passed in value was not recognized as an object of that type. The lack
of a specific error is because it's necessary to know whether the
value is *supposed* to be IPv4 or IPv6 in order to provide more detail
on why it has been rejected.

To support use cases where it is useful to have access to this
additional detail, the individual class constructors actually raise
the ``ValueError`` subclasses ``ipaddress.AddressValueError`` and
``ipaddress.NetmaskValueError`` to indicate exactly which part of the
definition failed to parse correctly.

The error messages are significantly more detailed when using the
class constructors directly. For example:

   >>> ipaddress.ip_address("192.168.0.256")
   Traceback (most recent call last):
     ...
   ValueError: '192.168.0.256' does not appear to be an IPv4 or IPv6 address
   >>> ipaddress.IPv4Address("192.168.0.256")
   Traceback (most recent call last):
     ...
   ipaddress.AddressValueError: Octet 256 (> 255) not permitted in '192.168.0.256'

   >>> ipaddress.ip_network("192.168.0.1/64")
   Traceback (most recent call last):
     ...
   ValueError: '192.168.0.1/64' does not appear to be an IPv4 or IPv6 network
   >>> ipaddress.IPv4Network("192.168.0.1/64")
   Traceback (most recent call last):
     ...
   ipaddress.NetmaskValueError: '64' is not a valid netmask

However, both of the module specific exceptions have ``ValueError`` as
their parent class, so if you're not concerned with the particular
type of error, you can still write code like the following:

   try:
       network = ipaddress.IPv4Network(address)
   except ValueError:
       print('address/netmask is invalid for IPv4:', address)
