# Catch-all subnets count should be retrievable

Catch-all subnets count should be retrievable. A Maester check for Active Directory, Sites and subnets.

Source: https://maester.dev/docs/tests/AD-SUB-03

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<div class="test-byline"><div class="test-byline-avatars"><a class="test-byline-avatar test-byline-avatar--author" href="/contributors/soulemike" title="Michael Soule · Original author"><img src="https://github.com/soulemike.png" alt="Michael Soule" width="28" height="28" loading="lazy" decoding="async" /></a></div><div class="test-byline-meta"><span class="test-byline-text">Contributed by <a href="/contributors/soulemike">Michael Soule</a></span><a class="test-byline-link" href="/contributors">All contributors →</a></div></div>

<p class="test-part">Part of <a href="/docs/tests/ad">Active Directory</a> · Active Directory · Sites and subnets · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId AD-SUB-03
```

## Overview

Catch-all subnets (overly broad IP ranges) can cause:

- **Authentication inefficiency**: Clients may authenticate to distant DCs
- **WAN congestion**: Unnecessary cross-site authentication traffic
- **Security concerns**: Difficult to track and audit client locations
- **Operational confusion**: Site boundaries don't reflect actual topology

Common catch-all subnets include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

#### Control Type

**Operational**

#### Security Recommendation

- Replace catch-all subnets with specific, appropriately-sized subnets
- Use /24 or smaller subnets for most locations
- Document exceptions where catch-all subnets are intentionally used
- Review subnet definitions during network planning

#### How the Test Works

This test identifies subnets with overly broad CIDR notation that could encompass multiple physical locations.

#### Related Tests

- `Test-MtAdSubnetNonInternalCount` - Identifies public IP subnets
- `Test-MtAdSubnetTotalCount` - Counts total subnets
- `Test-MtAdSiteWithoutSubnetCount` - Identifies sites without subnets

## Details

<details>
<summary>Every attribute of this check</summary>

| Field | Value |
| --- | --- |
| Test ID | AD-SUB-03 |
| Severity | Info |
| Suite | Active Directory |
| Product | Active Directory |
| Feature | Sites and subnets |
| Area | Infrastructure hardening |
| Resource type | AdSite |
| MITRE ATT&CK | None |
| PowerShell test | [Test-MtAdSubnetCatchAllCount](https://github.com/maester365/maester/blob/main/tests/ad/site/Test.AD-SUB-03.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:subnet:ReadProperty |

</details>

## Source

- Test: [`tests/ad/site/Test.AD-SUB-03.ps1`](https://github.com/maester365/maester/blob/main/tests/ad/site/Test.AD-SUB-03.ps1)
- Documentation: [`tests/ad/site/Test.AD-SUB-03.md`](https://github.com/maester365/maester/blob/main/tests/ad/site/Test.AD-SUB-03.md)