Subnet picker - Generate non-overlapping list of CIDRs based on base CIDR and existing subnets

subnet_picker.py

#!/usr/bin/env python3
import argparse
import ipaddress
import re
import sys


def main(results):
    # Convert existing_subnet to ip_network object
    existing_subnets = []
    if results.existing_subnet:
        try:
            existing_subnets = [
                ipaddress.ip_network(net) for net in results.existing_subnet
            ]
        except ValueError as e:
            print(e)
            sys.exit(1)

    # Sanity checks
    try:
        base_network = ipaddress.ip_network(results.base_cidr)
    except ValueError:
        print(f"{results.base_cidr} is not a valid network.")
        sys.exit(1)

    if not base_network.is_private:
        print(f"{base_network} is not a private network.")
        sys.exit(1)

    # Generate possible subnets list
    new_nets = []
    for new_subnet in results.new_subnet:
        new_bits, num_of_subnets = new_subnet.split("=")
        networks = base_network.subnets(int(new_bits))

        available_nets = []
        for net in networks:
            # Check overlap
            overlapping = any(net.overlaps(ex_subnet) for ex_subnet in existing_subnets)
            if not overlapping:
                available_nets.append(net)
        new_nets_of_bits = available_nets[: int(num_of_subnets)]
        new_nets.extend(new_nets_of_bits)
        existing_subnets.extend(new_nets_of_bits)
    print("\n".join([format(i) for i in new_nets]))


def check_new_subnet(val):
    if not re.compile(r"^\d+=\d+").match(val):
        raise argparse.ArgumentTypeError(
            "New subnet must be in the format: new_bits:num_of_subnets\n\
I.E: 5=3 - 3 new subnets with 5 new bits from the base CIDR"
        )
    return val


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "-b", "--base-cidr", default=None, help="Base CIDR to create subnets from"
    )
    parser.add_argument(
        "-e",
        "--existing-subnet",
        action="append",
        help="Existing subnet (specify multiple times for multiple subnets)",
    )

    parser.add_argument(
        "new_subnet",
        nargs="+",
        type=check_new_subnet,
        help="Subnet to create. new_bits=num_of_subnets. I.E: 2=5 will result\
        in 5 new subnets and each will be 2 bits more than the base",
    )
    results = parser.parse_args()
    main(results)