# Core Protocols

Active Directory relies on several core protocols to perform functions related to authentication, authorization, replication, directory access, and resource discovery.

We will give details of some of these protocols, and here we find a summary of their purposes:

* **Kerberos:** It's the default authentication protocol in Active Directory. It's based on tickets to provide mutual authentication and supports delegation
* **NTLM:** NT LAN Manager is a legacy authentication protocol, used when Kerberos isn’t available. It's less secure than Kerberos, being vulnerable to relay and brute-force attacks
* **LDAP:** Lightweight Directory Access Protocol is used to query and manage AD objects (users, groups, OUs, etc. It also has a secure version (LDAPS) that works over SSL/TLS
* **DRS:** The Directory Replication Protocol is used by Domain Controllers to synchronize changes in the directory. Runs over the Remote Procedure Call (RPC) protocol
* **DNS:** Domain Name System is essential for locating domain controllers and AD services, storing service location records. A dynamic version is also used (DDNS) to allow clients and DCs to automatically update their DNS records
* **SMB:** Server Message Block is a management and file sharing protocol used for file sharing, GPO delivery, and logon scripts
