Your company has an Active Directory forest named contoso.com. You plan to deploy an Exchange
Server 2010 organization that will contain two servers. Each server will have the Client Access server
role, the Hub Transport server role, and the Mailbox server role installed. You plan to add both
servers to a database availability group (DAG).
You need to recommend a high-availability solution for the Client Access server role. Your solution
must ensure that users are not prompted to authenticate if a Client Access server becomes
unavailable. What should you recommend?
A.
Create and configure a Client Access server array, and then install a hardware load balancer.
B.
Create and configure a Client Access server array, and then install Windows Network Load
Balancing on both servers.
C.
Deploy Microsoft Internet Security and Acceleration (ISA) Server 2006, and then implement DNS
round robin.
D.
Deploy Microsoft Internet Security and Acceleration (ISA) Server 2006, and then install Windows
Network Load Balancing.
Explanation:
A is the correct answer for this question.
While it is possible to install the Windows Network Load Balancing for a client access array that
solution will not work for this question.
Windows Network Load Balancing
Windows Network Load Balancing (WNLB) is the most common software load balancer used for
Exchange servers. There are several limitations associated with deploying WNLB with Microsoft
Exchange.
WNLB can’t be used on Exchange servers where mailbox DAGs are also being used because WNLB is
incompatible with Windows failover clustering. If you’re using an Exchange 2010 DAG and you want
to use WNLB, you need to have the Client Access server role and the Mailbox server role running on
separate servers.
Due to performance issues, we don’t recommend putting more than eight Client Access servers in an
array that’s load balanced by WNLB.
WNLB doesn’t detect service outages. WNLB only detects server outages by IP address. This means if
a particular Web service, such as Outlook Web App, fails, but the server is still functioning, WNLB
won’t detect the failure and will still route requests to that Client Access server. Manual intervention
is required to remove the Client Access server experiencing the outage from the load balancing pool.
WNLB configuration can result in port flooding, which can overwhelm networks.
Because WNLB only performs client affinity using the source IP address, it’s not an effective solution
when the source IP pool is small. This can occur when the source IP pool is from a remote network
subnet or when your organization is using network address translation.
http://technet.microsoft.com/en-us/library/ff625247.aspx