Fun with subnet fragmentation

file.py

from sys import argv
from ipaddress import IPv4Network
class SubnetUsage:
  def __init__(self, subnet_cidr):
    self.subnet_cidr = subnet_cidr
    self.network = IPv4Network(subnet_cidr)
    self.used = []
  
  def mark(self, ip_or_cidr):
    self.used.append(IPv4Network(ip_or_cidr))
    self.used = sorted(self.used)  # Lazy implementation of sorted list, sue me
  
  def is_allocatable(self, cidr):
    our_network = IPv4Network(cidr)
    return not any(map(lambda their_network: our_network.overlaps(their_network), self.used))
  
  def find_blocks(self, prefix=28):
    for block in self.network.subnets(new_prefix=prefix):
      if self.is_allocatable(block):
        yield block

def static_list():
  usage = SubnetUsage('172.18.106.0/24')

  usage.mark('172.18.106.0')
  usage.mark('172.18.106.1')
  usage.mark('172.18.106.2')
  usage.mark('172.18.106.3')
  usage.mark('172.18.106.255')

  # Single ENIs
  usage.mark('172.18.106.78')
  usage.mark('172.18.106.82')
  usage.mark('172.18.106.54')
  usage.mark('172.18.106.83')
  usage.mark('172.18.106.106')
  usage.mark('172.18.106.209')
  usage.mark('172.18.106.84')
  usage.mark('172.18.106.102')

  # ip ranges
  usage.mark('172.18.106.128/28')
  usage.mark('172.18.106.160/28')
  usage.mark('172.18.106.144/28')
  usage.mark('172.18.106.128/28')
  usage.mark('172.18.106.160/28')
  usage.mark('172.18.106.144/28')
  usage.mark('172.18.106.16/28')
  usage.mark('172.18.106.32/28')
  usage.mark('172.18.106.192/28')
  usage.mark('172.18.106.224/28')
  usage.mark('172.18.106.112/28')
  usage.mark('172.18.106.176/28')
  
  return usage

def _per_subnet_usage(ec2, subnet_id):
  cidr_block = ec2.describe_subnets(SubnetIds=[subnet_id])['Subnets'][0]['CidrBlock']
  enis = ec2.describe_network_interfaces(Filters=[{'Name':'subnet-id','Values':[subnet_id]}])['NetworkInterfaces']
  
  usage = SubnetUsage(cidr_block) 
  for iface in enis:
    usage.mark(iface['PrivateIpAddress'])

    if 'Ipv4Prefixes' in iface:
      for prefix in iface['Ipv4Prefixes']:
        usage.mark(prefix['Ipv4Prefix'])
  
  return usage

def aws_per_subnet_usage():
  import boto3
  ec2 = boto3.client('ec2', region_name='eu-central-1')

  subnet_id = input('Enter subnet ID: ')
  return _per_subnet_usage(ec2, subnet_id)

def aws_per_vpc_availability():
  import boto3
  ec2 = boto3.client('ec2', region_name='eu-central-1')

  vpc_id = input('VPC ID? ')
  all_subnets = ec2.describe_subnets(Filters=[{'Name':'vpc-id', 'Values': [vpc_id]}])['Subnets']
  all_usages = map(lambda subnet: list(_per_subnet_usage(ec2, subnet['SubnetId']).find_blocks(28)), all_subnets)
  return zip(map(lambda subnet: subnet['SubnetId'], all_subnets), all_usages)

if len(argv) <= 1 or argv[1] == 'static':
  usage = static_list()
  blocks = list(usage.find_blocks(28))
  print(f'Static list of IPs: The gathered subnet has {len(blocks)} free blocks of size /28')  
elif argv[1] == 'aws_subnet':
  usage = aws_per_subnet_usage()
  blocks = list(usage.find_blocks(28))
  print(f'AWS subnet: The specified subnet has >> {len(blocks)} << free blocks of size /28')
elif argv[1] == 'aws_vpc':
  for subnet, available_blocks in aws_per_vpc_availability():
    print(f'Subnet {subnet} has >> {len(available_blocks)} << free blocks of size /28')