What is Port 636?

by Colin Cohen | Published on November 13, 2023

Port 636 is for making encrypted LDAP (Lightweight Directory Access Protocol) so users can securely access protected network resources. These connections grant LDAP clients the ability to make use of directory services on LDAP servers.

Active Directory Port 636 Explained

Directory services, such as Microsoft Active Directory (now known as Entra), use port 636 to make secure connections between LDAP clients and servers. When a user requires directory services, such as when logging into a network or when locating and using a network printer, the LDAP client makes the requests over port 636 using SSL/TLS encryption.

How LDAP 636 Works

When a user requires an LDAP resource, such as a network printer, the following occurs: 

1. The LDAP client makes a secure connection to the LDAP server over port 636 using SSL/TLS encryption.

2. The client initiates a search query on the server.

3. The server authenticates the user.

4. The server performs the search and sends information about the resource to the client.

5. The LDAP connection closes, and the user accesses the resource.

Does Port 636 Use TCP or UDP?

LDAP supports both TCP and UDP transport protocols, though you will most likely use TCP when you are making queries on the LDAP server. Keep in mind that if you are using Microsoft AD (now known as Microsoft Entra ID) as the directory service, you will be using both protocols.

Is TCP LDAP Port 636 Encrypted?

When using LDAP over port 636, LDAP clients make encrypted connections to an LDAP server using SSL/TLS. LDAP clients can make unencrypted connections to an LDAP server over port 389, which is the default LDAP port.

What is Port 636 Used For?

You use port 636 for making secure LDAP connections. These connections allow users to access network devices as well as organizational data.

Devices That Rely on LDAP (SSL/TLS) 636

Any device that requires access to protected network resources relies on using LDAP over port 636. Also, devices such as network printers rely on LDAP so users can find them and securely connect to them.

Encrypted Communication Over Active Directory Port 636

You must use SSL/TLS encryption when using LDAP over port 636. Both the clients and the server must use the same encryption, which allows an LDAP client to connect to resources on the LDAP server securely.

LDAP SSL Port Manages User Accounts

Often, organizations will use LDAP for managing user accounts and access. When a user requires access to applications and data within the organization’s network, the LDAP server will authenticate them prior to granting them the necessary access.

Retrieving Organizational Data With LDAP Port 636

Organizations will frequently store data about their structure in an LDAP directory so their users can access it. For example, if a user wants to send an email to someone in their organization, the LDAP client will help them search for this person’s email address by making a query to the organization’s LDAP server.

Is LDAP 636 or 389?

LDAP can use either port 636 or port 389. You use port 636 for connections encrypted with SSL/TLS and port 389 for unencrypted connections.

What is Lightweight Directory Access Protocol Over SSL/TLS?

Using port 636, LDAPS takes the LDAP protocol one step further by adding SSL/TLS encryption. By using it, you can provide directory services more securely than you can by using the unencrypted version of LDAP.

LDAPS Explained

LDAPS is the secure version of LDAP. It takes all the features of traditional LDAP and adds SSL/TLS encryption to make the connections secure. This eliminates vulnerabilities associated with transmitting sensitive information in plain text.

LDAP vs LDAPS

LDAP and LDAPS make use of the same protocol to provide directory services to users. The only difference is that LDAPS adds SSL/TLS encryption, which makes the connections far more secure than traditional LDAP.

Does LDAP Port 636 Use Other Protocols Besides LDAPS?

When you use LDAP over port 636, you also use other protocols. You use TCP and UDP as transport protocols between the devices, and you use SSL/TLS protocols for encrypting communication.

What are Some Security Vulnerabilities With LDAPS 636?

By using the secure version of LDAP (LDAPS), you can eliminate many of the vulnerabilities associated with the unsecured version of the protocol, as it encrypts sensitive data. But you still must protect against LDAP injection attacks, and you must implement an up-to-date version of SSL/TLS.

SSL/TLS Implementation Errors

When implementing SSL/TLS for use with LDAP, it is important to use the most up-to-date version of the protocols. Implementing an older version of SSL/TLS, such as TLS 1.0 or TLS 1.1, can lead to critical vulnerabilities. These can include POODLE, BEAST, Heartbleed, and CRIME.

Avoiding LDAPS Configuration Mistakes

A common configuration mistake when implementing LDAPS is not validating or sanitizing user input prior to initiating LDAP queries. This can lead to LDAP injection attacks, which are similar to SQL injections and can result in executing unauthorized queries and allowing improper content modification. To mitigate these attacks, you should escape all user input prior to processing it.

What are Potential Port Conflicts with LDAPS Port 636?

When implementing LDAPS on port 636, you need to avoid conflicts with other services. You can either stop the existing service before starting LDAPS, or you can run the LDAPS service on a different port.

Can Multiple Services Interrupt Port 636?

Port 636 works like all other TCP ports in that only one service can listen to the port at one time. If you are experiencing a conflict on port 636, you must stop the existing service before starting the new one.

Can You Run Multiple LDAPS Services Simultaneously?

You cannot run multiple LDAPS services simultaneously on the same port. But you can run multiple LDAP services simultaneously on different ports. This means configuring one service to use port 636 and configuring the other services to use different ports.

Conclusion

LDAP is an important means of providing directory services in a network. By implementing the secure version of LDAP on port 636, you can ensure users will be able to access important resources safely. However, care must be taken to implement and configure it properly in order to avoid vulnerabilities.