A Note on IP Versions¶

For readers that aren't particularly familiar with IP addressing, it'simportant to know that the Internet Protocol (IP) is currently in the processof moving from version 4 of the protocol to version 6. This transition isoccurring largely because version 4 of the protocol doesn't provide enoughaddresses to handle the needs of the whole world, especially given theincreasing number of devices with direct connections to the internet.

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

IP Host Addresses¶

Addresses, often referred to as "host addresses" are the most basic unitwhen working with IP addressing. The simplest way to create addresses isto use theipaddress.ip_address() factory function, which automaticallydetermines whether to create an IPv4 or IPv6 address based on the passed invalue:

>>>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 willfit 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 beinvoked directly. This is particularly useful to force creation of IPv6addresses 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')

定義網路¶

Host addresses are usually grouped together into IP networks, soipaddress provides a way to create, inspect and manipulate networkdefinitions. IP network objects are constructed from strings that define therange of host addresses that are part of that network. The simplest formfor that information is a "network address/network prefix" pair, where theprefix defines the number of leading bits that are compared to determinewhether or not an address is part of the network and the network addressdefines the expected value of those bits.

As for addresses, a factory function is provided that determines the correctIP 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 thisis that192.0.2.1/24 does not describe a network. Such definitions arereferred to as interface objects since the ip-on-a-network notation iscommonly used to describe network interfaces of a computer on a given networkand are described further in the next section.

By default, attempting to create a network object with host bits set willresult inValueError being raised. To request that theadditional bits instead be coerced to zero, the flagstrict=False canbe 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 canalso be defined with integers, just like host addresses. In this case, thenetwork is considered to contain only the single address identified by theinteger, 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 forcedby calling the class constructor directly instead of using the factoryfunction.

Host Interfaces¶

As mentioned just above, if you need to describe an address on a particularnetwork, neither the address nor the network classes are sufficient.Notation like192.0.2.1/24 is commonly used by network engineers and thepeople who write tools for firewalls and routers as shorthand for "the host192.0.2.1 on the network192.0.2.0/24", Accordingly,ipaddressprovides a set of hybrid classes that associate an address with a particularnetwork. The interface for creation is identical to that for defining networkobjects, except that the address portion isn't constrained to being a networkaddress.

>>>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 IPversion can be forced by calling the relevant constructor directly.