For managed services providers (MSPs), Active Directory (AD) and Lightweight Directory Access Protocol (LDAP) are kitchen sink terms. So common and familiar are they that we rarely bother to discuss their functions and how to use them most effectively. This is unfortunate, if for no other reason than the fact that AD and LDAP are critical to all the work that we do as IT experts—within our own organizations and with our customers. For this reason, it is imperative that we understand these concepts thoroughly and reflect seriously on how they can be applied most effectively within our organizations.
To help facilitate this reflection and understanding, we have decided to lay out some of the key differences between AD and LDAP and explain the important relationships between them.
LDAP (Lightweight Directory Access Protocol) is an open and cross platform protocol used for directory services authentication.
LDAP provides the communication language that applications use to communicate with other directory services servers. Directory services store the users, passwords, and computer accounts, and share that information with other entities on the network.
Active Directory is a directory services implementation that provides all sorts of functionality like authentication, group and user management, policy administration and more.
Active Directory (AD) supports both Kerberos and LDAP – Microsoft AD is by far the most common directory services system in use today. AD provides Single-SignOn (SSO) and works well in the office and over VPN. AD and Kerberos are not cross platform, which is one of the reasons companies are implementing access management software to manage logins from many different devices and platforms in a single place. AD does support LDAP, which means it can still be part of your overall access management scheme.
Active Directory is just one example of a directory service that supports LDAP. There are other flavors, too: Red Hat Directory Service, OpenLDAP, Apache Directory Server, and more.
LDAP is a way of speaking to Active Directory.
LDAP is a protocol that many different directory services and access management solutions can understand.
The relationship between AD and LDAP is much like the relationship between Apache and HTTP:
Occasionally you’ll hear someone say, “We don’t have Active Directory, but we have LDAP.” What they probably mean is that they have another product, such as OpenLDAP, which is an LDAP server.
It’s kind of like someone saying “We have HTTP” when they really meant “We have an Apache web server.”
There are two options for LDAP authentication in LDAP v3 – simple and SASL (Simple Authentication and Security Layer).
Simple authentication allows for three possible authentication mechanisms:
SASL authentication binds the LDAP server to another authentication mechanism, like Kerberos. The LDAP server uses the LDAP protocol to send an LDAP message to the other authorization service. That initiates a series of challenge response messages that result in either a successful authentication or a failure to authenticate.
It’s important to note that LDAP passes all of those messages in clear text by default, so anyone with a network sniffer can read the packets. You need to add TLS encryption or similar to keep your usernames and passwords safe.