Your network contains an Active Directory domain named contoso.com. The domain contains two member
servers named Server1 and Server2. All servers run Windows Server 2012 R2.
Server1 and Server2 have the Network Load Balancing (NLB) feature installed. The servers are configured as
nodes in an NLB cluster named Cluster1. Both servers connect to the same switch.
Cluster1 hosts a secure web Application named WebApp1. WebApp1 saves user state information in a central
database.
You need to ensure that the connections to WebApp1 are distributed evenly between the nodes. The solution
must minimize port flooding.
What should you configure? To answer, configure the appropriate affinity and the appropriate mode for
Cluster1 in the answer area.
Hot Area:
Answer: 
Explanation:
http://technet.microsoft.com/en-us/library/cc782694(v=ws.10).aspx
Wth is wrong with the answer? Correct answer shows one thing and the explanation shows another… so confusing…
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I’d go for:
Afinity: None
The None option specifies that multiple connections from the same client IP address can be handled by different cluster hosts <– "connections to WebApp1 are distributed evenly between the nodes".
Mode: Multicast
With multicast, you can create static entries in the switch so that it sends the packets only to members of the NLB cluster. Mapping the address to the ports being used by the NLB cluster stops all ports from being flooded. Only the mapped ports will receive the packets for the NLB cluster instead of all ports in the switch. If you don’t create the static entries, it will cause switch flooding just like in unicast. <— "…solution must minimize port flooding".
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I would agree with this answer.
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the question states that a “secure web application” is hosted, so I think the secure channels will brake if you set affinity to “none” instead of “Client” (=aka “Single”)
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WebApp1 saves user state information in a database, so the affinity restriction would be relaxed. Affinity None is appropriate in this scenario.
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The explanation, Pikapoka and Den are correct.
“Client/server applications that manage client state so that it can be retrieved from any cluster host (for example, by embedding state within cookies or pushing it to a back-end database) do not need to use client affinity.”
https://msdn.microsoft.com/en-us/library/bb742455.aspx
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None
Multicast
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None
Multicast
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None
Session state is stored on a central database and you need to ensure nodes are balanced evenly. Using Single affinity or even class C will cause an imbalance and for no reason. Your session states are saved in that database.
Unicast
Unicast is always chosen as the better of the two evils between unicast and multicast unless you NEED multicast or you have a switch capable of VLANs or IGMP. Neither of these features are explicitly stated that they are supported, so I will assume that they are not. In this case, Unicast would be the only option.
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