AD LDS uses the concept of instances, similar to that of instances in SQL. What this means is one AD LDS server can run multiple AD LDS instances (databases). This is another differentiator from Active Directory: a domain controller can only be a domain controller for one domain. In AD LDS, each instance runs on a different set of ports. The default instance of AD LDS listens on 389 (similar to AD). You can run multiple instances of AD LDS concurrently on a single computer, with an independently managed schema for each AD LDS instance.