Reliable LDAP Monitoring

Keep your authentication and directory services available. Know when something's off before your users do.

How do you monitor LDAP and Active Directory health?

Reliable LDAP monitoring covers four areas: server availability, bind response time, domain controller replication health, and host-level resource capacity on the machines running the directory service. If any of those go unchecked, authentication issues and replication drift tend to surface as user complaints rather than something your monitoring caught first.

Paessler PRTG covers all four with dedicated sensors: the LDAP sensor for bind-based availability and response time, the AD Replication Errors sensor for DC sync health, and WMI-based sensors for CPU, memory, and disk on domain controllers. Everything runs agentless from the PRTG probe, no software deployed on the directory server itself. PRTG officially supports Microsoft Active Directory and Windows domain controllers, including encrypted connections via LDAPS on port 636 (SSL/TLS). All monitoring data feeds into dashboards that give you a combined view across your LDAP infrastructure.

Supported technologies: Microsoft Active Directory, Windows domain controllers, LDAPS (SSL/TLS, port 636)

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How PRTG Keeps Your LDAP Infrastructure Healthy

Stay on Top of LDAP Availability

LDAP is a silent dependency. VPN logins, internal apps, email, file access, access control for every endpoint on the network: all of it runs through the directory service. When an LDAP server becomes unreachable or a bind fails, none of those work, and IT finds out from user reports, not from their own tooling. PRTG checks availability via a real bind operation at configurable scan intervals, detects authentication failures, and sends an alert at the next check interval. The LDAP sensor officially supports Microsoft LDAP implementations, including Active Directory, on port 389 and port 636 (LDAPS with SSL/TLS).

Availability check via LDAP bind operation: tests the full authentication path, not just network reachability
Configurable scan intervals per server
Supports port 389 (standard) and port 636 (LDAPS with SSL/TLS)
Alert on server unreachable or authentication failure
Officially supports Microsoft LDAP implementations, including Active Directory

Get Ahead of Slow Authentication

LDAP servers rarely fail all at once. Response time drifts gradually, and by the time applications start timing out, the degradation has been building for a while. PRTG tracks bind response time continuously as its primary ldap monitoring channel, with configurable warning and critical thresholds you define yourself. You get alerted at the next check interval before the issue escalates, and historical trend data makes gradual performance degradation visible before it becomes a user-facing problem.

Continuous bind response time measurement
Configurable warning and critical thresholds per sensor
Historical data for spotting gradual degradation trends
Alert delivery via email, SMS, push, or webhook
Per-sensor threshold configuration, set independently per server

Keep All Your Domain Controllers in Sync

AD replication failures don't cause clean outages. A password change that doesn't apply everywhere, group policies that behave differently across sites, a user who can authenticate in one location but not another: troubleshooting these without replication health data means running manual repadmin checks that only show the current state. PRTG's AD Replication Errors sensor monitors each domain controller automatically at every check interval, tracking consecutive failures, pending replication operations, last sync attempt and result, and source DC information, so you catch drift early instead of after something breaks.

Per-DC replication error tracking
Consecutive synchronization failure counter
Pending replication operation count
Timestamp of last sync attempt and last successful sync
Indication of stalled or missing replication partners

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See the Full Picture

Response time problems don't always start at the protocol level. A domain controller running low on disk space or under sustained CPU load degrades authentication performance just as effectively, but you'd never see that by watching LDAP alone. In environments with multiple domain controllers handling load distribution, that blind spot compounds. PRTG monitors CPU load, memory, disk space, and I/O on domain controllers via WMI and Windows Performance Monitor counters, with SNMP available for bandwidth and network-level metrics. All sensors sit in the same device view as the LDAP sensor, giving you full observability across both layers of the stack.

CPU load, memory usage, and disk space monitoring via WMI
Pagefile and disk I/O tracking on Windows domain controllers
No agent required on the monitored server
LDAP sensor and WMI sensors co-located in the same device view
Historical data available for both layers for comparison

How PRTG Monitors LDAP and Directory Services

PRTG uses protocol-level checks and native Windows instrumentation to monitor LDAP and directory services. No agents are deployed on the directory server itself; monitoring runs from the PRTG probe.

LDAP Bind Authentication

An LDAP bind is a login command issued to the LDAP server. The PRTG LDAP sensor authenticates the way a real client would, sending credentials and waiting for a response. This means it tests the full authentication path, not just whether the server is reachable over the network. A ping can tell you the host is up; a bind tells you whether authentication is actually working.

The sensor requires a distinguished name (DN) and credentials, which are configurable per sensor instance. This lets you scope access precisely and monitor multiple servers with separate credentials independently. Note: the LDAP sensor supports IPv4 only. This applies to all connection types, including LDAPS. IPv6 is not supported.

Encrypted LDAP (LDAPS)

For encrypted connections, PRTG supports LDAPS on port 636 using SSL/TLS. Port 389 is available for standard unencrypted connections; the choice is configurable per sensor. Encrypting LDAP traffic is the standard approach for production environments, particularly where credential exposure is a vulnerability concern.

One important requirement when using SSL/TLS: the parent device in PRTG must be configured with a DNS name, not just an IP address. This is needed for certificate validation during the TLS handshake. Configuring LDAP monitoring with an IP address on the parent device will cause SSL/TLS connections to fail.

Host-Level Metrics

For host-level visibility on domain controllers, PRTG uses WMI and Windows Performance Monitor counters. Built-in sensor types (Windows CPU Load, WMI Memory, Windows Physical Disk I/O, Windows Pagefile) cover the metrics that matter for DC health. All of these are agentless; PRTG accesses the data remotely via WMI. For network-level data such as bandwidth utilization on the DC's network interface, PRTG supports SNMP as an additional protocol alongside WMI.

Where WMI overhead is a concern, PRTG also supports Windows performance counter-based access as an alternative. For custom monitoring needs beyond the built-in sensor types, PRTG’s PowerShell sensor lets you run scripts on the probe to collect custom data from monitored systems. The API-based access model is consistent across all Windows sensor types.

Alerts & Thresholds

PRTG sensors operate in defined states: Up, Warning, Down, Paused, Unknown, and Error. For threshold-based alerting, the relevant states are Up, Warning, and Down, where each one is tied to the ranges you configure per sensor. When a sensor crosses a threshold at the next scheduled check, it changes state and sends a notification through whichever channels you've set up: email, push notifications, SMS, or webhooks via API integrations.

Dashboards give you a visual overview of LDAP and DC sensor data across multiple servers in one place. You can review notification history and use notification triggers to route alerts to the right person or system. Notifications, thresholds, and delivery channels are all configurable per sensor.

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LDAP Monitoring With and Without PRTG

Capability	Without PRTG Without PRTG	With PRTG With PRTG
LDAP server availability check	Without PRTG Teams often rely on generic ping monitoring, which doesn’t verify whether LDAP authentication itself is functioning.	With PRTG Automated bind-based check detects authentication failures and unreachable servers at every configured scan interval.
Bind response time tracking	Without PRTG Response time degradation typically goes unnoticed until applications time out or users report slowness.	With PRTG Continuous bind response time measurement with configurable warning and critical thresholds. You’re alerted at the next check interval, before the issue escalates.
AD replication health	Without PRTG Manual repadmin checks per DC only show the state at the moment you run them.	With PRTG The AD Replication Errors sensor tracks failures, pending operations, and sync timestamps for every configured domain controller, at every check interval.
DC resource monitoring	Without PRTG Host-level metrics often require a separate tool and aren't visible alongside LDAP data.	With PRTG WMI-based sensors for CPU, memory, disk, and I/O sit in the same device view as the LDAP sensor.
Alert on failure	Without PRTG IT often learns about LDAP issues from help desk tickets, after users are already affected.	With PRTG Threshold-based alerts trigger at the next check interval and reach the right person via email, SMS, push, or webhook.

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LDAP Monitoring: Frequently Asked Questions

What exactly does an LDAP sensor measure?

The PRTG LDAP sensor measures two things: bind response time and server availability (Up/Down status). It does not measure ldap query volume, per-query search latency, or connection pool utilization. If you need those metrics, you'd need additional tooling beyond what the LDAP sensor provides.

Which LDAP implementations does PRTG support?

Microsoft Active Directory is officially supported and tested. OpenLDAP and other third-party LDAP providers may work in practice, but they're not officially supported. If you're running a non-Microsoft directory service on Linux or another operating system, verify compatibility in a test environment before deploying to production.

Does LDAP monitoring work with encrypted connections (LDAPS)?

Yes. PRTG supports LDAPS on port 636 using SSL/TLS. When using encrypted connections, the parent device in PRTG must be configured with a DNS name, not an IP address, for certificate validation to work. The entire LDAP sensor is IPv4-only; this applies to both standard and encrypted connections. Plain LDAP on port 389 is also available and configurable per sensor.

Can I monitor multiple domain controllers independently?

Yes. You deploy one LDAP sensor and one AD Replication Errors sensor per domain controller, each configured and tracked independently. This gives you per-DC visibility for both authentication availability and replication health across all your monitored servers.

What's the difference between the LDAP sensor and the AD Replication Errors sensor?

Different layers, different use cases. The LDAP sensor checks protocol-level availability and bind response time: it tells you whether the ldap service is responding and how fast. The AD Replication Errors sensor tracks DC-to-DC sync health, covering replication failures, pending operations, and sync timestamps. You typically need both to get a complete picture of Microsoft Active Directory health.

How does PRTG notify me when something goes wrong with LDAP?

When a sensor crosses a threshold at the next check interval, it changes state and sends a notification. Delivery options include email, push notifications, SMS, and API-based integrations (e.g., webhooks). Notifications are configurable per sensor, and dashboards give you an at-a-glance view across all monitored LDAP and DC devices. You can also set up notification triggers to route alerts based on sensor state.