DAG Subnet change in Virtualization Environment

I was working with one of my customer. He wanted to change IP/Subnet/AD site for an existing DAG member.



Changing subnet for existing DAG member server.



Change of AD site and IP/Subnet range in your organization.



Exchange 2010 SP1 and later

Windows server 2008 R2 SP1

AD Site: 2+

Virtualization: VMWare/Hyper-V

Example Subnet change from to


DAG networks and multiple subnet deployments:


In the preceding example, even though there are two different subnets in use by the DAG ( and, the DAG is considered a single-subnet DAG because each member uses the same subnet to form the MAPI network. When DAG members use different subnets for the MAPI network, the DAG is referred to as a multi-subnet DAG. In a multi-subnet DAG, the proper subnets are automatically with each DAG network.



  • We changed subnet in the network adapter on the target server.
  • Checked under “Failover Cluster Manager” and it was updated.
  • Checked DAG properties and found new subnet has been updated.
  • Assigned new IP to the target server.
  • Did ipconfig /flushdns to flush IP address.
  • Did ipconfig /registerdns to register new IP.
  • Still DAG is unable to pick new subnet.
  • Requested the you to reboot the server.
  • After reboot we  can still see the server and network is down under “Failover Cluster Manager”.
  • Also found DAG network is unable to bring the subnet online.
  • Confirmed that you added new subnet to VLAN as well.
  • As network is down under “Failover Cluster Manager” Microsoft involved cluster team.
  • In the mean time you made changes in production and it was successful.



To accomplish this we need to perform below steps.



  1. Suspend mailbox databases copies on the target server.
  2. Stop mail replication on the node by using the suspend-mailboxdatabasecopy command
  3. Stop all Exchange Services on the target server.
  4. Stop the cluster service
  5. Change the subnet AND IP address on the network card/adaptor.  Changing just the subnet itself will not write stuff correctly to the registry to make the change.  This might be a Hyper-V issue. 
  6. No need to delete the virtual NIC.
  7. Start the cluster service.  Verify that the new cluster network was created with the correct subnet.
  8. REGEDIT and modify this key



  1. When we restarted the cluster service, Exchange populates this key with the OLD subnet of the server.  Just need to change the part that was with 22 on the end.
  2. Close registry editor
  3. Restart target server.
  4. Logon to the server and change the IP address back to original IP.  Register with DNS
  5. Verify that the cluster service is still correct.  It will show that the change node down
  6. Launch the EMC.  Go to the DAG, remove the old subnet from the DAGNETWORK.  Once you do this, it will create a new DAGNETWORK automatically with the correct subnet.  Delete the DAGNETWORK (Old subnet network) that we changed since it’s not used anymore.
  7. Cluster service should show everything is happy.  Wait until DNS replicates before starting replication.
  8. Resume-mailboxdatabasecopy
  9. Done




Thank you,


Comments (0)

Skip to main content