Directory Replication

Directory replication ensures that directory information is current among servers. Directory information is automatically updated on all servers in the same site, and can be configured to be updated automatically with servers in other sites.

Each Microsoft Exchange Server computer has a local directory. At any given time, the local directories on two servers might contain different information. For example, if you create a new mailbox on server A, the addition won't show up on server B until the directory on server B gets updated through directory replication.

There are two directory replication processes: intrasite (within a site) and intersite (between sites). Intrasite directory replication does not need to be configured; it starts automatically. Intersite directory replication must be configured.

Directory Replication Within a Site

Intrasite replication is a way to distribute a directory among servers within a site. Each directory notifies the others of its changes. Directory replication within a site has the following characteristics:

• Every server has a copy of the directory that can be written to. This enables the directory changes to be made on any server.
• Every server has a direct connection with every other server in the site. This means that directory replication can start from any server in the site.
• Directory replication automatically starts within five minutes after a change to a directory object is made.
• Directory change notifications and requests for updates are done through remote procedure calls (RPCs).

During directory replication within a site:

• A directory change is made and other servers are notified of the change, one directory at a time.
• Each directory requests an update and is then updated.

Directory Replication Between Sites

To establish directory replication between sites, you configure a directory replication connector between them. You must establish mail connectivity between two sites before you can replicate their directories.

One server is required at each end point. The servers at each end point of a directory replication connector are called directory replication bridgehead servers, which request directory updates from each other. You can only configure one directory replication connector between two sites.

Directory replication between sites has the following characteristics:

Point-to-point   The replication bridgehead servers are the only two points of contact for replicating directory information between two sites. The following illustration shows directory replication between sites:

Scheduled   Intersite directory replication runs on a schedule that you set up. This schedule determines when a local site requests directory updates from the remote site.

Messaging-based   Communication between bridgehead servers is done through messages. Requests for updates, and the updates themselves, are sent as messages through MTAs and connectors.

During directory replication between sites:

1. A message is sent from the local site to request directory updates from the remote site.
2. The requested updates are sent from the remote site using messages.
3. The directory at the local site is updated.
4. All other directories at the local site are updated through intrasite replication.