AD database is stored in a single database file NTDS.dit is logically segmented into directory partitions or naming context

Domain partition

Configuration partition

Schema partition

Application partition

Logical partitions in NTDS.dit file

It is a set of definition for all object types in the directory and their related attributes.

A logical group of computer that share the same database.

A collection of domains that share contiguous namespace. This creates Trust automatically.

It is the top most logical container in an AD network. A collection of domains that share the same Schema. A trust is automatically created between domain trees.

A collection or group of well-connected networks. Allows you to divide up your network based on your network topology for service localization and to manage replication. Site can be separated by: location secure subnet (separated by a firewall) weak connection (via wifi)

Service localization

Manage replication

It contains the copy of the AD DS database. It can process changes and replicate the changes to all other DC in the domain. It only holds a copy of objects in its domain.

It holds the AD DS database. It uses Jet database technology and stores the information in the NTDS.dit file and associated logs. This is the physical structure of NTDS.dit

NTDS.DIT

EDB.LOG

EDB****.LOG

EDB.CHK

RES1.LOG, RES2.LOG

TEMP.EDB

Schema.INI

A writable DC that contains the full copy of a DC in the same domain and a partial read-only copy of all objects in the forest. This allows users and applications to find objects in any domain in the current forest. Not all attributes of objects from other domains in the forest are copied. You can add more attributes via AD Schema by selecting Replicate This Attribute to the Global Catalog. source: https://theitbros.com/global-catalog-active-directory/

It is mainly used for security purposes while providing resiliency at remote offices with poor connection. RODC replication is one directional and only happened during replication cycle and only with a writable DC not with other RODC.

Sites can be modeled based on your physical network

based on physical location

based on secure subnet (separated by firewall)

based on connectivity (weak WiFi)

Runs every 15mins

Manual run via Check Replication Topology

Creates connection between servers

Sites

Site link

Subnet

It creates a ring connection between DCs. If a site increases number of DCs for more than 8, additional connection will be made to ensure that there will be no more 3 hops between DCs. This ensures propagation happens within less that a minute (45sec in 3 hops).

Happens between DCs in the same Site

No configuration required

Starts 15sec after a change

Up to 3 hops propagation in less than 1min

Uses IP transport only

Replication between two sites

Requires a Site link

AD selects a bridge head server automatically in each site

You can select your Preferred bridge server

Bridge head server will replicate the change to bridge head server to other site

Has an option to use SMTP or IP transport

via AD Management Tool

via LDAP syntax