# Non-Global Catalog DC count should be retrievable

Global Catalogs (GCs) maintain a partial replica of all objects in the Active Directory forest, enabling:

Source: https://maester.dev/docs/tests/AD-DCD-04

<!-- This file is generated by website/scripts/generate-test-docs.mjs. Do not edit manually. -->

<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 · Domain controllers · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId AD-DCD-04
```

## Overview

Global Catalogs (GCs) maintain a partial replica of all objects in the Active Directory forest, enabling:

- **Forest-wide searches**: Users can search for objects across all domains in the forest
- **Universal group membership caching**: Required for authentication when universal groups are used
- **Efficient authentication**: Users can be authenticated even when their home domain's DC is unavailable

In a **single-domain environment**, all domain controllers should be Global Catalogs for optimal performance and redundancy. There's no downside to making all DCs GCs when there's only one domain.

In a **multi-domain forest**, proper Global Catalog placement is critical:
- Each site should have at least one GC for optimal authentication performance
- Too few GCs can cause authentication delays and failures
- Too many GCs can increase replication traffic

#### Control Type

**Operational**

#### Security Recommendation

1. **Single-domain forests**: Configure all DCs as Global Catalogs
2. **Multi-domain forests**: Ensure each site has at least one GC, preferably in the same site as the users
3. **Monitor GC health**: Regularly verify GCs are functioning properly
4. **Plan for GC failure**: Ensure redundant GC coverage for business-critical sites
5. **Universal group considerations**: If not using universal groups, GC requirements may be reduced, but GCs still provide benefits for directory searches

#### How the Test Works

This test retrieves all domain controllers and identifies which are configured as Global Catalogs. The test reports:

- Total number of domain controllers
- Number of DCs configured as Global Catalogs
- Number of DCs not configured as Global Catalogs
- Names of non-GC DCs (if any exist)
- Forest domain count to provide context for the configuration

The test provides different guidance based on whether the forest is single-domain or multi-domain.

#### Related Tests

- `Test-MtAdDcReadOnlyCount` - Analyzes RODC deployment
- `Test-MtAdDcSiteCoverageCount` - Analyzes DC distribution across sites
- `Test-MtAdForestDomainCount` - Determines the number of domains in the forest

## Details

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

| Field | Value |
| --- | --- |
| Test ID | AD-DCD-04 |
| Severity | Info |
| Suite | Active Directory |
| Product | Active Directory |
| Feature | Domain controllers |
| Area | Infrastructure hardening |
| Resource type | DomainController |
| MITRE ATT&CK | None |
| PowerShell test | [Test-MtAdDcNonGlobalCatalogCount](https://github.com/maester365/maester/blob/main/tests/ad/domain-controller/Test.AD-DCD-04.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:nTDSDSA:ReadProperty, ActiveDirectory:Ldap:crossRef:ReadProperty |

</details>

## Source

- Test: [`tests/ad/domain-controller/Test.AD-DCD-04.ps1`](https://github.com/maester365/maester/blob/main/tests/ad/domain-controller/Test.AD-DCD-04.ps1)
- Documentation: [`tests/ad/domain-controller/Test.AD-DCD-04.md`](https://github.com/maester365/maester/blob/main/tests/ad/domain-controller/Test.AD-DCD-04.md)