What should you identify?

Your network contains an Active Directory forest named contoso.com and two Active Directory sites
named Site1 and Site2. You plan to deploy an Exchange Server 2010 Service Pack 1 (SP1)
organization. An independent consultant recommends a design for the Exchange Server 2010 SP1
deployment as shown in the following table.

You are evaluating the implementation of the Hub Transport server role on EX4. You need to identify
which Exchange server configuration will minimize the loss of email messages sent between users of
the organization if a Hub Transport server fails. What should you identify?

A.
DNS round robin on DC1 and DC2

B.
Datacenter Activation Coordination (DAC) mode

C.
shadow redundancy

D.
delayed acknowledgments (ACKs)

E.
a Hosts file on EX1, EX2, EX3, and EX4

F.
a database availability group (DAG)

G.
a single copy cluster (SCC)

H.
an activation preference for a database

I.
EdgeSync synchronization

J.
a DNS server on DC2
K.
Edge Transport server cloned configuration
L.
local continuous replication (LCR) on EX1, EX2, EX3, and EX4

Explanation:
High availability strategies for Exchange have focused on the availability and recoverability of data
stored in mailbox databases. When you implement a highly available solution for your Mailbox
servers, the e-mail messages won’t be lost, and they can easily be recovered after a failure, after
they arrive in a mailbox.
However, these strategies didn’t extend to messages while they’re in transit. If a Hub Transport
server fails while processing messages and can’t be recovered, data loss could occur. As the volume
of messages processed by Hub Transport servers increases, potential data loss becomes an
increasing concern for administrators.
Microsoft Exchange Server 2007 introduced the transport dumpster feature for the Hub Transport
server role.
An Exchange 2007 Hub Transport server maintains a queue of messages delivered recently to
recipients whose mailboxes are on a clustered mailbox server. When a failover is experienced, the
clustered mailbox server automatically requests every Hub Transport server in the Active Directory

site to resubmit mail from the transport dumpster queue. This prevents mail from being lost during
the time taken for the cluster to fail over.
While this does provide a basic level of transport redundancy, it’s only available for message delivery
in a cluster continuous replication (CCR) environment and doesn’t address potential message loss
when messages are in transit between Hub Transport and Edge Transport servers.
Exchange Server 2010 introduces the shadow redundancy feature to provide redundancy for
messages for the entire time they’re in transit. The solution involves a technique similar to the
transport dumpster. With shadow redundancy, the deletion of a message from the transport
databases is delayed until the transport server verifies that all of the next hops for that message
have completed delivery. If any of the next hops fail before reporting back successful delivery, the
message is resubmitted for delivery to that next hop.
Shadow redundancy provides the following benefits:
• It eliminates the reliance on the state of any specific Hub Transport or Edge Transport server. As
long as redundant message paths exist in your routing topology, any transport server becomes
disposable.
• If a transport server fails, you can remove it from production without emptying its queues or losing
messages.
• If you want to upgrade a Hub Transport or Edge Transport server, you can bring that server offline
at any time without the risk of losing messages.
• It eliminates the need for storage hardware redundancy for transport servers.
• It consumes less bandwidth than creating duplicate copies of messages on multiple servers. The
only additional network traffic generated with shadow redundancy is the exchange of discard status
between transport servers. Discard status is the information each transport server maintains. It
indicates when a message is ready to be discarded from the transport database.
• It provides resilience and simplifies recovery from a transport server failure.