# IPv6 catch-all subnets count should be retrievable

Overly broad IPv6 subnets can cause similar issues to IPv4 catch-all subnets:

Source: https://maester.dev/docs/tests/AD-SUB-05

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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-05
```

## Overview

Overly broad IPv6 subnets can cause similar issues to IPv4 catch-all subnets:

- **Authentication inefficiency**: Clients may authenticate to distant DCs
- **Suboptimal routing**: Site boundaries don't reflect actual topology
- **Management complexity**: Difficult to track client locations
- **Security concerns**: Reduced granularity in access controls

IPv6 /48 prefixes or larger are considered catch-all ranges.

#### Control Type

**Operational**

#### Security Recommendation

- Use appropriately-sized IPv6 subnets (typically /64 for client networks)
- Align IPv6 subnet boundaries with physical locations
- Document IPv6 subnet allocation scheme
- Review IPv6 subnet definitions regularly

#### How the Test Works

This test identifies IPv6 subnets with overly broad prefixes (/48 or smaller).

#### Related Tests

- `Test-MtAdSubnetIpv6Count` - Counts IPv6 subnets
- `Test-MtAdSubnetCatchAllCount` - Identifies IPv4 catch-all subnets
- `Test-MtAdSubnetTotalCount` - Counts total subnets

## Details

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

| Field | Value |
| --- | --- |
| Test ID | AD-SUB-05 |
| 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-MtAdSubnetIpv6CatchAllCount](https://github.com/maester365/maester/blob/main/tests/ad/site/Test.AD-SUB-05.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:subnet:ReadProperty |

</details>

## Source

- Test: [`tests/ad/site/Test.AD-SUB-05.ps1`](https://github.com/maester365/maester/blob/main/tests/ad/site/Test.AD-SUB-05.ps1)
- Documentation: [`tests/ad/site/Test.AD-SUB-05.md`](https://github.com/maester365/maester/blob/main/tests/ad/site/Test.AD-SUB-05.md)