Uma introdução ao módulo ipaddress¶
Este documento tem como objetivo prover uma suave introdução ao módulo
ipaddress. Ele é direcionado primeiramente para usuários que ainda não são familiarizados com a terminologia de rede IP, mas também pode ser útil para engenheiros de rede que querem uma visão geral de como
ipaddress representa os conceitos de endereçamento de rede IP.
Criando objetos de Endereço/Rede/Interface¶
A Note on IP Versions¶
For readers that aren’t particularly familiar with IP addressing, it’s important to know that the Internet Protocol (IP) 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
>>> 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')
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
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
ValueError being raised. To request that the
additional bits instead be coerced to zero, the flag
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.
As mentioned just above, if you need to describe an address on a particular
network, neither the address nor the network classes are sufficient.
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
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
>>> 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.
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) 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 IPv4Address('192.0.2.1') >>> net4[-1] IPv4Address('192.0.2.255') >>> net6 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('126.96.36.199/24') False
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
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
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
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)