Check if two CIDR addresses intersect?

Question

Given two CIDR addresses say 192.168.2.0/14 and 192.168.2.0/32

How do I check if two ip addresses overlap in "python2.6"??

I have gone through netaddr and it allows to check if 192.168.2.0 is in CIDR address 192.168.2.0/14 by

from netaddr import IPNetwork, IPAddress
bool = IPAddress("192.168.2.0") in IPNetwork("192.168.2.0/14"):

But how to check for two CIDR address??

I found a reference :: How can I check if an ip is in a network in python

FYI, 192.168.2.0/32 is a single IP address (192.168.2.0), not a subnet. — slebetman, Jun 20 '13 at 06:37
Thnx for the info. I need it in python but your explanation might be useful. — AjanShrestha, Jun 20 '13 at 07:33

score 41 · Accepted Answer · answered Jun 20 '13 at 06:46

41

Using ipaddr:

>>> import ipaddr
>>> n1 = ipaddr.IPNetwork('192.168.1.0/24')
>>> n2 = ipaddr.IPNetwork('192.168.2.0/24')
>>> n3 = ipaddr.IPNetwork('192.168.2.0/25')
>>> n1.overlaps(n2)
False
>>> n1.overlaps(n3)
False
>>> n2.overlaps(n3)
True
>>> n2.overlaps(n1)
False

answered Jun 20 '13 at 06:46

falsetru

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Thanks the library does exactly what I want. – AjanShrestha Jun 20 '13 at 07:55
Does the same code work for IPv6 as well or it supports IPv4 only? – AjanShrestha Jun 20 '13 at 07:56
Work for IPv6. `ipaddr.IPNetwork('::192.168.0.0/120').overlaps(ipaddr.IPNetwork('::192.168.0.0/121'))` returns True and `ipaddr.IPNetwork('::192.168.4.0/120').overlaps(ipaddr.IPNetwork('::192.168.0.0/121'))` returns False – falsetru Jun 20 '13 at 08:11
Is there any solution in Powershell? – user6264 Feb 16 '21 at 09:24
Is there an online tool for this? – Rajesh Swarnkar Mar 06 '23 at 08:49

rob mayoff · Answer 2 · 2013-06-20T06:48:37.357

7

I'll assume you actually want both CIDRs to represent ranges, even though in your example, 192.168.2.0/32 represents only one address. Also note that in 192.168.2.0/14, the .2. is meaningless, because the 14-bit prefix doesn't reach the third octet.

Anyway, there are a several ways to do this. You could notice that for them to overlap, one must always be a subset of the other:

def cidrsOverlap(cidr0, cidr1):
    return cidr0 in cidr1 or cidr1 in cidr0

Or you could notice that for the ranges to overlap, the first range's lowest address must be less than or equal to the second range's highest address, and vice versa. Thus:

def cidrsOverlap(cidr0, cidr1):
    return cidr0.first <= cidr1.last and cidr1.first <= cidr0.last

print cidrsOverlap(IPNetwork('192.168.2.0/24'), IPNetwork('192.168.3.0/24'))
# prints False

print cidrsOverlap(IPNetwork('192.168.2.0/23'), IPNetwork('192.168.3.0/24'))
# prints True

edited Jun 20 '13 at 06:48

answered Jun 20 '13 at 06:42

rob mayoff

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Thanks the range comparison works. One more thing, could you find out the ip addresses that are overlapped?? – AjanShrestha Jun 20 '13 at 07:54
2

The ip addresses that are overlapped is the subnet with the smaller range: that is, the higher number after the `/`. Therefore, between 192.168.2.0/23 and 192.168.2.0/24 the addresses that are overlapped are 192.168.2.0/24. Remember, CIDR subnet cannot "overlap". They can only contain a smaller CIDR subnet or not. – slebetman Jun 20 '13 at 08:03
@AJRedDevil Since one is always a subset of the other, the overlap is just the smaller range. The first address in the overlap (smaller range) is `max(cidr0.first, cidr1.first)`. The last address is `min(cidr0.last, cidr1.last)`. – rob mayoff Jun 20 '13 at 08:11

score 5 · Answer 3 · answered Jun 04 '19 at 13:33

5

I wrote this simple command line tool, based on the netaddr lib.

pip install ipconflict

Example:

ipconflict 10.0.0.0/22 10.0.1.0/24

Output:

conflict found: 10.0.1.0/24 <-> 10.0.1.0/22

answered Jun 04 '19 at 13:33

shishax

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Sylvain Leroux · Answer 4 · 2013-06-20T06:48:28.690

If don't have netaddr at hand for testing, but I think you could check if the first and last address of the first network are both contained in the second:

net_1 = IPNetwork("192.168.2.0/14")
net_2 = IPNetwork("192.168.2.0/32")
if net_1.first in net_2 and net_1.last in net_2:
    # do something

BTW, IPNetwork line 1102 defines a __contains__ method. But I'm not certain the line 1127 isn't broken ? You should test and report a bug if it is.

Check if two CIDR addresses intersect?

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