REF: Planning Exchange 2010 DAG - Part 1 - Network Requirements

 

Planning for High Availability and Site Resilience  - Network Requirements

(a single MAPI network/ one or more Replication networks)
In Exchange 2010, each DAG will have multiple networks: a single MAPI network, which is used by other Exchange 2010 servers to communicate with the Mailbox server in the DAG, and one or more Replication networks, which are used for log shipping and seeding within the DAG. It's important that the DAG networks are configured correctly.

(two adapters/ MAPI network failover/ Replication network revert to MAPI Network/ )
Each member of the DAG must have at least two network adapters installed. This configuration provides you with one MAPI network and one Replication network, and the following recovery behaviors:

• In the event of a failure affecting the MAPI network, a server failover will occur (assuming there are healthy mailbox database copies that can be activated).
• In the event of a failure affecting the Replication network, if the MAPI network is unaffected by the failure, log shipping and seeding operations will revert to use the MAPI network. When the failed Replication network is restored, log shipping and seeding operations will revert back to the Replication network.

• Each DAG should have a single MAPI network in each DAG. The MAPI network must provide connectivity to other Exchange servers and other services, such as Active Directory and DNS.
• Additional Replication networks can be added, as needed. You can prevent an individual MAPI or Replication network from being a single point of failure by using network adapter teaming or similar technology.
• Each network in each DAG member server must be on its own network subnet. Each server in the DAG can be on a different subnet, but the MAPI and Replication networks must be routable and provide connectivity, such that:
  • Each network in each DAG member server is on its own network subnet that's separate from the subnet used by each other network in the server.
  • Each DAG member server's MAPI network can communicate with each other DAG member's MAPI network.
  • Each DAG member server's Replication network can communicate with each other DAG member's Replication network.
  • There is no direct routing that allows heartbeat traffic from the Replication network on one DAG member server to the MAPI network on another DAG member server, or vice versa.
    
• Regardless of their geographic location relative to other DAG members, each member of the DAG must have round trip network latency no greater than 250 milliseconds (ms) between each other member.
• Round trip latency requirements may not be the most stringent network bandwidth and latency requirement for a multi-data center configuration. You must evaluate the total network load, which includes client access, Active Directory, transport, continuous replication, and other application traffic, to determine the necessary network requirements for your environment.
• DAG networks support Internet Protocol Version 4 (IPv4) and IPv6. IPv6 is supported only when IPv4 is also used; a pure IPv6 environment isn't supported. Using IPv6 addresses and IP address ranges is supported only when both IPv6 and IPv4 are enabled on that computer, and the network supports both IP address versions. If Exchange 2010 is deployed in this configuration, all server roles can send data to and receive data from devices, servers, and clients that use IPv6 addresses.
• Automatic Private IP Addressing (APIPA) is a feature of Microsoft Windows that automatically assigns IP addresses when no Dynamic Host Configuration Protocol (DHCP) server is available on the network. APIPA addresses (including manually assigned addresses from the APIPA address range) aren't supported for use by DAGs or by Exchange 2010.

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More Information & Reference
1. Planning for High Availability and Site Resilience