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Understanding Edge Subscription Credentials

Applies to: Exchange Server 2010

Topic Last Modified: 2010-01-18

This topic explains how the Edge Subscription process provisions the credentials that are used to help secure the EdgeSync synchronization process in Microsoft Exchange Server 2010 and how the Microsoft Exchange EdgeSync service uses those credentials to establish a secure LDAP connection between a Hub Transport server and an Edge Transport server. To learn more about the Edge Subscription process, see Understanding Edge Subscriptions.

Looking for management tasks related to managing transport servers? See Managing Transport Servers.

Contents

Edge Subscription Process

EdgeSync Replication Accounts

Authenticating Initial Replication

Authenticating Scheduled Synchronization Sessions

Renewing EdgeSync Replication Accounts

The Edge Transport server is subscribed to an Active Directory site to establish a synchronization relationship between the Hub Transport servers in an Active Directory site and the subscribed Edge Transport server. The credentials that are provisioned during the Edge Subscription process are used to help secure the LDAP connection between a Hub Transport server and an Edge Transport server in the perimeter network.

When you run the New-EdgeSubscription cmdlet in the Exchange Management Shell on an Edge Transport server, the EdgeSync bootstrap replication account (ESBRA) credentials are created in the Active Directory Lightweight Directory Services (AD LDS) directory on the local server and then written to the Edge Subscription file. These credentials are used only to establish the initial synchronization and will expire 1,440 minutes (24 hours) after the Edge Subscription file is created. If the Edge Subscription process isn't completed within that time, you must run the New-EdgeSubscription cmdlet in the Shell on the Edge Transport server again to create an Edge Subscription file.

The following table describes the data contained in the Edge Subscription XML file.

Edge Subscription file contents

Subscription data Description

EdgeServerName

The NetBIOS name of the Edge Transport server. The name of the Edge Subscription in Active Directory will match this name.

EdgeServerFQDN

The fully qualified domain name (FQDN) of the Edge Transport server. The Hub Transport servers in the subscribed Active Directory site must be able to locate the Edge Transport server by using Domain Name System (DNS) to resolve the FQDN.

EdgeCertificateBlob

The public key of the Edge Transport server's self-signed certificate.

ESRAUsername

The name assigned to the ESBRA. The ESBRA account has the following format: ESRA.Edge Transport server name. ESRA means EdgeSync replication account.

ESRAPassword

The password assigned to the ESBRA. The password is generated by using a random number generator and is stored in the Edge Subscription file in clear text.

EffectiveDate

The creation date of the Edge Subscription file.

Duration

The length of time that these credentials will be valid before they expire. The ESBRA account is valid for only 24 hours.

AdamSslPort

The secure LDAP port to which the EdgeSync service binds when synchronizing data from Active Directory to AD LDS. By default, this is TCP port 50636.

ProductID

The licensing information for the Edge Transport server. After an Edge Transport server is subscribed to Active Directory, the licensing information about the Edge Transport server is displayed in the Exchange Management Console for the Exchange organization. You must license the Edge Transport server before you create the Edge Subscription for this information to be displayed correctly.

VersionNumber

The version number of the Edge Subscription file.

SerialNumber

The version of Exchange Server that is installed on the Edge Transport server.

Bb266959.important(en-us,EXCHG.140).gifImportant:
The ESBRA credentials are written to the Edge Subscription file in clear text. You must protect this file throughout the subscription process. After the Edge Subscription file is imported to your Exchange organization, you should immediately delete the Edge Subscription file from the Edge Transport server, the network share you used to import the file to your Exchange organization, and any removable media.

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EdgeSync replication accounts (ESRA) are an important part of EdgeSync security. Authentication and authorization of the ESRA is the mechanism used to help secure the connection between an Edge Transport server and a Hub Transport server.

The ESBRA contained in the Edge Subscription file is used to establish a secure LDAP connection during the initial synchronization. After the Edge Subscription file is imported to a Hub Transport server in the Active Directory site to which the Edge Transport server is being subscribed, additional ESRA accounts are created in Active Directory for each Edge Transport-Hub Transport server pair. During initial synchronization, the newly created ESRA credentials are replicated to AD LDS. These ESRA credentials are used to help secure later synchronization sessions.

Each EdgeSync replication account is assigned the properties described in the following table.

Ms-Exch-EdgeSyncCredential properties

Property name Type Description

TargetServerFQDN

String

The Edge Transport server that will accept these credentials.

SourceServerFQDN

String

The Hub Transport server that will present these credentials. This value is empty if the credential is the bootstrap credential.

EffectiveTime

DateTime (UTC)

When to start using this credential.

ExpirationTime

DateTime (UTC)

When to stop using this credential.

UserName

String

The user name that's used to authenticate.

Password

Byte

The password that's used to authenticate. The password is encrypted by using ms-Exch-EdgeSync-Certificate.

The following sections of this topic describe how the ESRA credentials are provisioned and used during the EdgeSync synchronization process.

When the New-EdgeSubscription cmdlet is run on the Edge Transport server, the ESBRA is provisioned as follows:

  • A self-signed certificate (Edge-Cert) is created on the Edge Transport server. The private key is stored in the local computer store and the public key is written to the Edge Subscription file.
  • The ESBRA (ESRA.Edge) is created in AD LDS, and the credentials are written to the Edge Subscription file.
  • The Edge Subscription file is exported by copying it to removable media. The file is now ready to import to a Hub Transport server.

When the Edge Subscription file is imported on a Hub Transport server, the following steps occur to establish a record of the Edge Subscription in Active Directory and to provision additional ESRA credentials.

  1. An Edge Transport server configuration object is created in Active Directory. The Edge-Cert certificate is written to this object as an attribute.
  2. Every Hub Transport server in the subscribed Active Directory site receives an Active Directory notification that a new Edge Subscription has been registered. As soon as the notification is received, each Hub Transport server retrieves the ESRA.Edge account and encrypts the account by using the Edge-Cert public key. The encrypted ESRA.Edge account is written to the Edge Transport server configuration object.
  3. Each Hub Transport server creates a self-signed certificate (Hub-Cert). The private key is stored in the local computer store and the public key is stored in the Hub Transport server configuration object in Active Directory.
  4. Each Hub Transport server encrypts the ESRA.Edge account by using the public key of its own Hub-Cert certificate and then stores it in its own configuration object.
  5. Each Hub Transport server generates an ESRA for each existing Edge Transport server configuration object in Active Directory (ESRA.Hub.Edge). The account name is generated by using the following naming convention:
    ESRA.<Hub Transport server NetBIOS Name>.<Edge Transport server NetBIOS Name>.<Effective Date UTC Time>
    Example: ESRA.Hub.Edge.01032010
    The password for ESRA.Hub.Edge is generated by a random number generator and is encrypted by using the public key of the Hub-Cert certificate. The generated password has the maximum length allowed for Microsoft Windows Server.
  6. Each ESRA.Hub.Edge account is encrypted by using the public key of the Edge-Cert certificate and is stored on the Edge Transport server configuration object in Active Directory.

The following sections of this topic explain how these accounts are used during the EdgeSync synchronization process.

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The ESBRA account, ESRA.Edge, is used only when establishing the initial synchronization session. During the first EdgeSync synchronization session, the additional ESRA accounts, ESRA.Hub.Edge, are replicated to AD LDS. These accounts are used to authenticate later EdgeSync synchronization sessions.

The Hub Transport server that performs the initial replication is determined randomly. The first Hub Transport server in the Active Directory site to perform a topology scan and discover the new Edge Subscription performs the initial replication. Because this discovery is based on the timing of the topology scan, any Hub Transport server in the site may perform the initial replication.

The Microsoft Exchange EdgeSync service initiates a secure LDAP session from the Hub Transport server to the Edge Transport server. The Edge Transport server presents its self-signed certificate and the Hub Transport server verifies that the certificate matches the certificate that's stored on the Edge Transport server configuration object in Active Directory. After the Edge Transport server's identity is verified, the Hub Transport server provides the credentials of the ESRA.Edge account to the Edge Transport server. The Edge Transport server verifies the credentials against the account that's stored in AD LDS.

The Microsoft Exchange EdgeSync service on the Hub Transport server then pushes the topology, configuration, and recipient data from Active Directory to AD LDS. The change to the Edge Transport server configuration object in Active Directory is replicated to AD LDS. AD LDS receives the newly added ESRA.Hub.Edge entries and the Microsoft Exchange Credential Service creates the corresponding AD LDS account. These accounts are now available to authenticate later scheduled EdgeSync synchronization sessions.

The Microsoft Exchange Credential Service is part of the Edge Subscription process. It runs only on the Edge Transport server. This service creates the reciprocal ESRA accounts in AD LDS so that a Hub Transport server can authenticate to an Edge Transport server to perform EdgeSync synchronization. The Microsoft Exchange EdgeSync service doesn't communicate directly with the Microsoft Exchange Credential Service. The Microsoft Exchange Credential Service communicates with AD LDS and installs the ESRA credentials whenever the Hub Transport server updates them.

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After initial EdgeSync synchronization finishes, the EdgeSync synchronization schedule is established and data that has changed in Active Directory is regularly updated in AD LDS. A Hub Transport server initiates a secure LDAP session with the AD LDS instance on the Edge Transport server. AD LDS proves its identity to that Hub Transport server by presenting its self-signed certificate. The Hub Transport server presents its ESRA.Hub.Edge credentials to AD LDS. The ESRA.Hub.Edge password is encrypted by using the Hub Transport server's self-signed certificate's public key. This means that only that particular Hub Transport server can use those credentials to authenticate to AD LDS.

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The password for the ESRA account must comply with the local server's password policy. To prevent the password renewal process from causing temporary authentication failure, a second ESRA.Hub.Edge account is created seven days before the first ESRA.Hub.Edge account expires with an effective time that's three days before the first ESRA expiration time. As soon as the second ESRA account becomes effective, EdgeSync stops using the first account and starts to use the second account. When the expiration time for the first account is reached, those ESRA credentials are deleted. This renewal process will continue until the Edge Subscription is removed.

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