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Namespace Models: Bounded vs Unbounded

Exchange 2016 uses two different types of namespaces wherein Servers are deployed in multiple Data Centers. Let’s see what are those and how it works.

1. Bounded Model:

Deploying the dedicated namespace for the each site in the site resilient pair.


In above diagram, Bangalore and Chennai Sites has it’s own Namespaces called (Bangalore site) & Site). In public DNS both are pointed to the respective Data center VIP#(Virtual IP Address).


  1. Each Data Center has it’s own dedicated namespace.

  2.  Preferred for the Active Data center and Disaster Recovery Data Center model. with this preference to have the users operate out of one datacenter during normal operations and only have the users operate out of the second datacenter during failure events.

  3.  In a bound model, there are two DAGs deployed in the datacenter pair. Each DAG contains a set of mailbox databases for a particular datacenter; by controlling where the databases are mounted, you control connectivity.


  1. In a bound model, multiple namespaces are required for Each Data Center.

  2. Switchover to the other Datacenter during failure events is controlled event.

  3. Clients will fail to connect in case there is a no connectivity to the Data Center.

2. Unbounded Model:

In an unbound model, you have a single DAG deployed across the datacenter pair.


In above diagram, Both the Data centers VIP# addresses are pointed to a Single Namespace called Basically it will be Round-Robin in the DNS. If one Primary Site not reachable, DNS will fail back to Secondary Site without any issues. It’s typically preferred in case the DAG is spanned across two different sites.


  1. Single namespace is required for both the Datacenters.

  2. Clients can connect to other datacenter automatically in case of there is a WAN Failure event.

  3. Clients will get better experience to connect to the datacenters.

  4. Both the VIPs will be load balanced as both of them are participating in the Clients connectivity.


  1. In case Databases are controlled within one Site, 50% of the traffic proxied to the other site.

Both of them has it’s merits and demerits. It is up to you selecting the Namespace models which required for your companies.

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