An Odd Situation in Which GCP VPC Firewall Rules Are Missing yet Still Active

Firewall Rules Gone, but Their Impact Remains: Understanding GCP's Hidden Policies

Imagine logging into your Google Cloud Platform (GCP) project, expecting to see your well-defined firewall rules, only to find them missing. 😲 This is exactly what happened to our organization when we reviewed our firewall settings after three years. Despite their absence from the interface, these rules still influence access to our resources.

This issue became evident when certain IPs could connect seamlessly while others faced access restrictions. For instance, our team members working remotely without the company VPN couldn't access BigQuery or storage buckets. The VPN’s whitelisted IP was the only key to entry.

Such a scenario raises critical questions: Have these rules been relocated? Did a recent update alter their visibility? Or is this a case of shadow policies persisting in the background? Understanding what’s happening is crucial to regaining control over network security.

If you’ve faced a similar issue, you’re not alone. This article explores possible reasons why your firewall rules may have vanished yet remain operational, along with solutions to track and modify them effectively. 🔍

Investigating Disappearing Firewall Rules in GCP

When dealing with missing firewall rules in Google Cloud Platform (GCP), the scripts we developed aim to uncover hidden configurations that might still be enforcing access controls. The first approach uses Python with the Google Cloud SDK to list active firewall rules. By leveraging the compute_v1.FirewallsClient(), we can query all firewall settings applied to a project, even if they don’t appear in the standard UI. This script is particularly useful for administrators who suspect that legacy rules are still affecting network traffic. Imagine a developer struggling to connect to BigQuery outside the company VPN—this script helps reveal if an outdated rule is still restricting access. 🔍

The second approach utilizes the gcloud command-line interface (CLI) to fetch firewall rules directly from GCP. The command gcloud compute firewall-rules list --filter="sourceRanges:YOUR_IP" allows filtering results by IP range, which is extremely valuable when diagnosing network access issues. For example, if a teammate working remotely reports being blocked from accessing cloud storage, running this command can quickly determine whether their IP is whitelisted or restricted. By using gcloud compute security-policies list, we also check for organization-wide security policies that might be overriding project-specific rules. This is crucial because certain firewall configurations may no longer be managed at the project level but rather by the organization itself. 🏢

Another powerful technique involves using Terraform to manage firewall rules as infrastructure-as-code. The Terraform script retrieves firewall rule definitions via data "google_compute_firewall", making it easier to track changes over time. This approach is especially useful for teams that prefer automation and version control. For example, if an IT administrator needs to ensure that all security policies remain consistent across environments, they can use Terraform to query and verify firewall configurations. The output "firewall_details" command then displays the retrieved rules, helping teams compare expected versus actual settings. This is beneficial when dealing with unexpected access restrictions in cloud environments where multiple engineers manage security policies.

In summary, these scripts help solve the mystery of disappearing firewall rules by offering multiple methods—Python for programmatic analysis, the CLI for quick checks, and Terraform for structured infrastructure management. Whether investigating a blocked API request, debugging VPN access, or validating security policies, these solutions provide practical ways to regain control over GCP firewall settings. By combining these approaches, organizations can ensure that no hidden rule disrupts their cloud operations, preventing unnecessary downtime and access frustrations. 🚀

from google.cloud import compute_v1
def list_firewall_rules(project_id):
    client = compute_v1.FirewallsClient()
    request = compute_v1.ListFirewallsRequest(project=project_id)
    response = client.list(request=request)
    for rule in response:
        print(f"Name: {rule.name}, Source Ranges: {rule.source_ranges}")
if __name__ == "__main__":
    project_id = "your-gcp-project-id"
    list_firewall_rules(project_id)

# Authenticate with Google Cloud if not already done
gcloud auth login
# Set the project ID
gcloud config set project your-gcp-project-id
# List all firewall rules in the project
gcloud compute firewall-rules list --format=json
# Check if any rules apply to a specific IP
gcloud compute firewall-rules list --filter="sourceRanges:YOUR_IP"
# Check if rules are managed by an organization policy
gcloud compute security-policies list

provider "google" {
  project = "your-gcp-project-id"
  region  = "us-central1"
}
data "google_compute_firewall" "default" {
  name    = "firewall-rule-name"
}
output "firewall_details" {
  value = data.google_compute_firewall.default
}

How GCP’s Firewall Architecture Impacts Hidden Rules

One lesser-known aspect of Google Cloud Platform (GCP) firewall rules is how they are structured across different levels. GCP allows firewall rules to be defined at both the project and organization levels. This means that even if a specific project appears to have no firewall rules, there might still be active policies inherited from the organization or network hierarchy. For example, an enterprise-wide security policy may block all incoming traffic except from whitelisted VPN IPs, which could explain why some users have access while others don’t. 🔍

Another key factor is the presence of VPC Service Controls, which add an additional layer of security by restricting access to sensitive resources like BigQuery and Cloud Storage. If these controls are enabled, even a properly configured firewall rule might not be enough to grant access. In real-world scenarios, companies using GCP for large-scale data processing often enforce these controls to prevent unauthorized data exfiltration. This can create confusion when developers assume their firewall settings are the primary access control mechanism, not realizing there are multiple layers at play. 🏢

To further complicate matters, GCP also utilizes dynamic firewall rules managed through IAM roles and Cloud Armor. While IAM permissions define which users can apply changes to firewall rules, Cloud Armor can enforce security policies dynamically based on threat intelligence and geographic rules. This means that a rule you applied months ago could be overridden by a security update without it being visibly removed from the UI. Understanding these different layers is crucial for effectively managing network security in GCP.