List all GCP IPv4 network blocks using the cloud-netblocks TXT records.

list_gcp_network_blocks.py

import json

from dns.resolver import Resolver

dns_resolver = Resolver()


def _parse_netblock_includes(txt):
    includes = set()
    ip4_blocks = set()
    for txt_entry in txt.split():
        if txt_entry.startswith("include:"):
            includes.add(txt_entry.split(":")[1])
        elif txt_entry.startswith("ip4:"):
            ip4_blocks.add(txt_entry.split(":")[1])

    return includes, ip4_blocks


def list_gcp_network_blocks():
    """Enumerate every IPv4 block GCP uses by querying cloud-netblocks TXT records.
    """
    gcp_ip4_blocks = set()
    netblocks = ["_cloud-netblocks.googleusercontent.com"]
    while netblocks:
        netblock = netblocks.pop(0)
        for nb_answer in dns_resolver.query(netblock, "TXT"):
            for txt_record in nb_answer.strings:
                includes, ip4_blocks = _parse_netblock_includes(
                    txt_record.decode("utf-8")
                )
                netblocks.extend(includes)
                gcp_ip4_blocks.update(ip4_blocks)

    return gcp_ip4_blocks


blocks = list(list_gcp_network_blocks())
print(json.dumps(blocks))