LDAP（Lightweight Directory Access Protocol）とは？

LDAP (Lightweight Directory Access Protocol) is an application-layer protocol defined by the IETF that enables clients to search, read, and modify entries in hierarchical directory services over IP networks, commonly used for user authentication and identity data lookups via TCP connections to directory servers. The protocol operates on a client-server model where clients connect to a directory server, authenticate through bind operations, and send requests such as search, compare, add, modify, and delete operations, with data organized as a tree of entries identified by distinguished names and access controlled by server-side rules. Security and operational reliability depend heavily on proper configuration including encrypted connections (TLS on port 636 or StartTLS on port 389), least-privilege service accounts, certificate validation, redundant servers, and protection against LDAP injection attacks, as outages or misconfigurations can block logins across entire organizations that depend on centralized directory access.