Known issues: Secure LDAP alerts in Microsoft Entra Domain Services

Applications and services that use lightweight directory access protocol (LDAP) to communicate with Microsoft Entra Domain Services can be configured to use secure LDAP. An appropriate certificate and required network ports must be open for secure LDAP to work correctly.

This article helps you understand and resolve common alerts with secure LDAP access in Domain Services.

AADDS101: Secure LDAP network configuration

Alert message

Secure LDAP over the internet is enabled for the managed domain. However, access to port 636 is not locked down using a network security group. This may expose user accounts on the managed domain to password brute-force attacks.


When you enable secure LDAP, it's recommended to create extra rules that restrict inbound LDAPS access to specific IP addresses. These rules protect the managed domain from brute force attacks. To update the network security group to restrict TCP port 636 access for secure LDAP, complete the following steps:

  1. In the Microsoft Entra admin center, search for and select Network security groups.
  2. Choose the network security group associated with your managed domain, such as, then select Inbound security rules
  3. Select + Add to create a rule for TCP port 636. If needed, select Advanced in the window to create a rule.
  4. For the Source, choose IP Addresses from the drop-down menu. Enter the source IP addresses that you want to grant access for secure LDAP traffic.
  5. Choose Any as the Destination, then enter 636 for Destination port ranges.
  6. Set the Protocol as TCP and the Action to Allow.
  7. Specify the priority for the rule, then enter a name such as RestrictLDAPS.
  8. When ready, select Add to create the rule.

The managed domain's health automatically updates itself within two hours and removes the alert.


TCP port 636 isn't the only rule needed for Domain Services to run smoothly. To learn more, see the Domain Services Network security groups and required ports.

AADDS502: Secure LDAP certificate expiring

Alert message

The secure LDAP certificate for the managed domain will expire on [date]].


Create a replacement secure LDAP certificate by following the steps to create a certificate for secure LDAP. Apply the replacement certificate to Domain Services, and distribute the certificate to any clients that connect using secure LDAP.

Next steps

If you still have issues, open an Azure support request for more troubleshooting help.