alanwill - 1 year ago 178
Python Question

# Splitting a network into subnets of multiple prefixes

I'm using the

`netaddr`
module and trying to figure out how/if I can split a network into subnets of varying prefixes. For example take a /16 and split it into X /23s and Y /24s.

From what I can tell we can use the
`subnet`
function to split a network in X number of a given prefix but it only takes 1 prefix.

The above would slice out 4 /23s out of the /16 which is great, but how do I take the remaining space and slice that into a differing prefix?

``````ip = IPNetwork('172.24.0.0/16')
subnets = list(ip.subnet(23, count=4))
``````

Is there a way that I can achieve what I'm trying to do with netaddr?

Try the below

``````from netaddr import IPNetwork, cidr_merge, cidr_exclude

class IPSplitter(object):
def __init__(self, base_range):
self.avail_ranges = set((IPNetwork(base_range),))

def get_subnet(self, prefix, count=None):
for ip_network in self.get_available_ranges():
subnets = list(ip_network.subnet(prefix, count=count))
if not subnets:
continue
self.remove_avail_range(ip_network)
self.avail_ranges = self.avail_ranges.union(set(cidr_exclude(ip_network, cidr_merge(subnets)[0])))
return subnets

def get_available_ranges(self):
return sorted(self.avail_ranges, key=lambda x: x.prefixlen, reverse=True)

def remove_avail_range(self, ip_network):
self.avail_ranges.remove(ip_network)
``````

You can use it like below. With some more math you can make it more efficient,like chopping of subnets from two different blocks when count is not satisfied from a single block.

``````In [1]: from ip_splitter import IPSplitter

In [2]: s = IPSplitter('172.24.0.0/16')

In [3]: s.get_available_ranges()
Out[3]: [IPNetwork('172.24.0.0/16')]

In [4]: s.get_subnet(23, count=4)
Out[4]:
[IPNetwork('172.24.0.0/23'),
IPNetwork('172.24.2.0/23'),
IPNetwork('172.24.4.0/23'),
IPNetwork('172.24.6.0/23')]

In [5]: s.get_available_ranges()
Out[5]:
[IPNetwork('172.24.8.0/21'),
IPNetwork('172.24.16.0/20'),
IPNetwork('172.24.32.0/19'),
IPNetwork('172.24.64.0/18'),
IPNetwork('172.24.128.0/17')]

In [6]: s.get_subnet(28, count=10)
Out[6]:
[IPNetwork('172.24.8.0/28'),
IPNetwork('172.24.8.16/28'),
IPNetwork('172.24.8.32/28'),
IPNetwork('172.24.8.48/28'),
IPNetwork('172.24.8.64/28'),
IPNetwork('172.24.8.80/28'),
IPNetwork('172.24.8.96/28'),
IPNetwork('172.24.8.112/28'),
IPNetwork('172.24.8.128/28'),
IPNetwork('172.24.8.144/28')]

In [7]: s.get_available_ranges()
Out[7]:
[IPNetwork('172.24.8.128/25'),
IPNetwork('172.24.9.0/24'),
IPNetwork('172.24.10.0/23'),
IPNetwork('172.24.12.0/22'),
IPNetwork('172.24.16.0/20'),
IPNetwork('172.24.32.0/19'),
IPNetwork('172.24.64.0/18'),
IPNetwork('172.24.128.0/17')]
``````
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