If you are wondering how to pick up a suitable IP subnet, try the ipaddress module. The following code snippet shows an example of how to choose a specific subnet, based on the number of necessary host IP addresses for a small private network.

Suppose you have a CIDR network address, such as 192.168.0.0/24, and you want to generate a range of all the IP addresses that it represents (192.168.0.1 to 192.168.0.254). The ipaddress module can be easily used to perform such calculations:

>>> import ipaddress
 >>> net = ipaddress.ip_network('192.168.0.0/24')
 >>> net
 IPv4Network('192.168.0.0/24')
 >>> for a in net:
 ...     print(a)
 ...
 192.168.0.1
 192.168.0.2
 192.168.0.3
 ...
 192.168.0.254

In this example, we are using the ip_network method from the ipaddress module to generate a range of all the IP addresses that represent the network.

You can find the following code in the net_ip_planner.py file:

!/usr/bin/env python3

import ipaddress as ip

CLASS_C_ADDR = '192.168.0.0'

mask = input("Enter the mask len (24-30): ")
mask = int(mask)
if mask not in range(23, 31):
    raise Exception("Mask length must be between 24 and 30")

net_addr = CLASS_C_ADDR + '/' + str(mask)
print("Using network address:%s " %net_addr)

try:
    network = ip.ip_network(net_addr)
except:
    raise Exception("Failed to create network object")

print("This mask will give %s IP addresses" %(network.num_addresses))
print("The network configuration will be:")
print("	 network address: %s" %str(network.network_address))
print("	 netmask: %s" %str(network.netmask))
print("	 broadcast address: %s" %str(network.broadcast_address))
first_ip, last_ip = list(network.hosts())[0], list(network.hosts())[-1]
print("	 host IP addresses: from %s to %s" %(first_ip,last_ip))

The following is the execution of the previous script for some masks and the C class IP address, 192.168.0.0:

• Execution with mask 24:

Enter the mask len (24-30): 24
 Using network address:192.168.0.0/24
 This mask will give 256 IP addresses
 The network configuration will be:
         network address: 192.168.0.0
         netmask: 255.255.255.0
         broadcast address: 192.168.0.255
         host IP addresses: from 192.168.0.1 to 192.168.0.254

• Execution with mask 30:

Enter the mask len (24-30): 30
 Using network address:192.168.0.0/30
 This mask will give 4 IP addresses
 The network configuration will be:
         network address: 192.168.0.0
         netmask: 255.255.255.252
         broadcast address: 192.168.0.3
         host IP addresses: from 192.168.0.1 to 192.168.0.2