Efficiently create a number of subnets out of a larger prefix

do-vlsm.py

#!/bin/env/python
from __future__ import print_function
import ipaddress

def do_vlsm(sorted_vlans):
    supernet = input("Supernet: ") or "192.168.224.0/20"
    current_subnet = ipaddress.ip_network(supernet)
    available_subnets = [current_subnet]
    print("\nSubnet Lengths:")
    for vlan in sorted_vlans:
        if vlan['subnet_len'] == 0:
            print("VLAN: {} will not be used.".format(vlan['name']))
        else:
            tentative_subnet = ''
            for x in range(0, 32):
                if tentative_subnet:
                    break
                for subnet in available_subnets:
                    if subnet.prefixlen == vlan['subnet_len'] - x:
                        tentative_subnet = list(subnet.subnets(new_prefix=vlan['subnet_len']))[0]
                        available_subnets = (available_subnets
                                             + list(subnet.address_exclude(tentative_subnet)))
                        remaining_subnets = []
                        for a in available_subnets[:]:
                            if not a.overlaps(tentative_subnet):
                                remaining_subnets.append(a)
                        available_subnets = remaining_subnets
                        vlan['subnet'] = str(tentative_subnet)
                        break

    print("Used Prefixes:")
    print("name,vid,prefix")
    for vlan in sorted_vlans:
        print("{},{},{}".format(vlan['name'], vlan['vlan_id'], vlan['subnet']))

    print("Remaining Prefixes:")
    for subnet in sorted(available_subnets):
        print(subnet)
    return sorted_vlans, available_subnets, supernet

def get_vlan_input():
    vlans = []
    print("Leave VLAN blank when finished")
    while(True):
        vlan_name = input("VLAN Name: ")
        if not vlan_name:
            break
        vlan_id = input("VLAN ID: ")
        if not 1 <= int(vlan_id) <= 4094:
            vlan_id = input("VLAN ID must be 1-4094: ")
        subnet_len = input("Subnet length: /")
        if not 0 <= int(subnet_len) <= 32:
            subnet_len = input("Subnet Len must be 0-32: /")
        vlans.append({'name': vlan_name, 'subnet_len': int(subnet_len), 'vlan_id': vlan_id})
    return sorted(vlans, key=lambda k: k['subnet_len'])

do_vlsm(get_vlan_input())

pip install ipaddress