Python - ip <-> subnet match? [duplicate]

Question

Possible Duplicate:
How can I check if an ip is in a network in python

What is the easy way to match subnet to an ip address in python, so that if the ip address is in the subnet I can choose it?

Thanks in advance.

Shostakovich

It's really not clear what you're asking. What are you choosing, the IP or the subnet? Is the question "how can I tell if an IP address is in a particular subnet?" Or what? – Anstice

Answer 1

In Python 3.3+, you can use ipaddress module:

>>> import ipaddress
>>> ipaddress.ip_address('192.0.43.10') in ipaddress.ip_network('192.0.0.0/16')
True

If your Python installation is older than 3.3, you can use this backport.

---

If you want to evaluate a lot of IP addresses this way, you'll probably want to calculate the netmask upfront, like

n = ipaddress.ip_network('192.0.0.0/16')
netw = int(n.network_address)
mask = int(n.netmask)

Then, for each address, calculate the binary representation with one of

a = int(ipaddress.ip_address('192.0.43.10'))
a = struct.unpack('!I', socket.inet_pton(socket.AF_INET, '192.0.43.10'))[0]
a = struct.unpack('!I', socket.inet_aton('192.0.43.10'))[0]  # IPv4 only

Finally, you can simply check:

in_network = (a & mask) == netw

Contraption

anyway to do this more efficiently for a giant set of tables? ex. I have a table of some 100,000 of these :) – Pergolesi

@EiyrioüvonKauyf Updated the answer for that case as well. – Contraption

The second approach, which calculates the netmask upfront, does not seem to work. I followed the exact step, and in the end, in_network is False. I am using the port of the module to 2.6 and 2.7. Using ipaddr (code.google.com/p/ipaddr-py) is the same: yielding a False for the above example. Note that I imported the py module files directly without run the setup.py, which I don't think is an issue. – Mandatory

@Mandatory Great catch! Fixed by switching to ints. – Contraption

Has since been imported to older python versions. – Synergism

@BelminFernandez Thanks, I've added the backport (by yours truly ;) ) to the answer. – Contraption

Answer 2

If for a given IP you want to find a prefix from a long list of prefixes, then you can implement longest prefix match. You first build a prefix tree from your list of prefixes, and later, you traverse the tree looking for the furthest leaf that matches your prefix.

It sounds scary, but it is not that bad :)

Nenitanenney