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.

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

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 :)