
Explanation/Reference:
Explanation:
A DAG network is a collection of one or more subnets used for either replication traffic or MAPI traffic.
Each DAG contains a maximum of one MAPI network and zero or more replication networks.
In a single network adapter configuration, the network is used for both MAPI and replication traffic.
In a two-network configuration, one network is typically dedicated for replication traffic, and the other network is used primarily for MAPI traffic. You can also add network adapters to each DAG member and configure additional DAG networks as replication networks. A two-network configuration is the recommended configuration.
There are several items to keep in mind when configuring DAG networks:
There must be one MAPI network. If there is not going to be a replication network, the MAPI network

will be used for replication.
Replication networks are optional. There can be multiple replication networks. If the replication network

fails, the DAG will fail back to the MAPI network for replication.
If you want to utilize a replication network, it must reside on a different subnet than the MAPI network.

This often makes it difficult to use a replication network when building a DAG across multiple locations.
The reason being that multiple WAN connections would be needed in order to separate the MAPI traffic from the replication traffic.
Each server within a DAG must have the same number of replication networks. This means that you

cannot use a replication network between two local Mailbox servers and not use a replication network for a server that is a member of the same DAG located across a WAN connection.
STEPS
DAGNET1 must be ReplicationEnabled
DAGNET2 must be MapiAccessEnabled to fulfill the requirements
References:http://technet.microsoft.com/en-us/library/dd298065(v=exchg.150).aspx