Prepare network mapping for Hyper-V VM disaster recovery to Azure
This article helps you to understand and prepare for network mapping when you replicate Hyper-V VMs in System Center Virtual Machine Manager (VMM) clouds to Azure, or to a secondary site, using the Azure Site Recovery service.
Prepare network mapping for replication to Azure
When you're replicating to Azure, network mapping maps between VM networks on a source VMM server, and target Azure virtual networks. Mapping does the following:
- Network connection—Ensures that replicated Azure VMs are connected to the mapped network. All machines which fail over on the same network can connect to each other, even if they failed over in different recovery plans.
- Network gateway—If a network gateway is set up on the target Azure network, VMs can connect to other on-premises virtual machines.
Network mapping works as follows:
- You map a source VMM VM network to an Azure virtual network.
- After failover Azure VMs in the source network will be connected to the mapped target virtual network.
- New VMs added to the source VM network are connected to the mapped Azure network when replication occurs.
- If the target network has multiple subnets, and one of those subnets has the same name as subnet on which the source virtual machine is located, then the replica virtual machine connects to that target subnet after failover.
- If there’s no target subnet with a matching name, the virtual machine connects to the first subnet in the network.
Example
Here's an example to illustrate this mechanism. Let's take an organization with two locations in Beijing and Shanghai.
| Location | VMM server | VM networks | Mapped to |
|---|---|---|---|
| Beijing | VMM-Beijing | VMNetwork1-Beijing | Mapped to VMNetwork1-Shanghai |
| VMNetwork2-Beijing | Not mapped | ||
| Shanghai | VMM-Shanghai | VMNetwork1-Shanghai | Mapped to VMNetwork1-Beijing |
| VMNetwork2-Shanghai | Not mapped |
In this example:
- When a replica VM is created for any VM that's connected to VMNetwork1-Beijing, it will be connected to VMNetwork1-Shanghai.
- When a replica VM is created for VMNetwork2-Beijing or VMNetwork2-Shanghai, it won't be connected to any network.
Here's how VMM clouds are set up in our example organization, and the logical networks associated with the clouds.
Cloud protection settings
| Protected cloud | Protecting cloud | Logical network (Beijing) |
|---|---|---|
| GoldCloud1 | GoldCloud2 | |
| SilverCloud1 | SilverCloud2 | |
| GoldCloud2 | NA |
LogicalNetwork1-Beijing LogicalNetwork1-Shanghai |
| SilverCloud2 | NA |
LogicalNetwork1-Beijing LogicalNetwork1-Shanghai |
Logical and VM network settings
| Location | Logical network | Associated VM network |
|---|---|---|
| Beijing | LogicalNetwork1-Beijing | VMNetwork1-Beijing |
| Shanghai | LogicalNetwork1-Shanghai | VMNetwork1-Shanghai |
| LogicalNetwork2Shanghai | VMNetwork2-Shanghai |
Target network settings
Based on these settings, when you select the target VM network, the following table shows the choices that will be available.
| Select | Protected cloud | Protecting cloud | Target network available |
|---|---|---|---|
| VMNetwork1-Shanghai | SilverCloud1 | SilverCloud2 | Available |
| GoldCloud1 | GoldCloud2 | Available | |
| VMNetwork2-Shanghai | SilverCloud1 | SilverCloud2 | Not available |
| GoldCloud1 | GoldCloud2 | Available |
If the target network has multiple subnets and one of those subnets has the same name as the subnet on which the source virtual machine is located, then the replica virtual machine will be connected to that target subnet after failover. If there's no target subnet with a matching name, the virtual machine will be connected to the first subnet in the network.
Failback behavior
To see what happens in the case of failback (reverse replication), let's assume that VMNetwork1-Beijing is mapped to VMNetwork1-Shanghai, with the following settings.
| VM | Connected to VM network |
|---|---|
| VM1 | VMNetwork1-Network |
| VM2 (replica of VM1) | VMNetwork1-Shanghai |
With these settings, let's review what happens in a couple of possible scenarios.
| Scenario | Outcome |
|---|---|
| No change in the network properties of VM-2 after failover. | VM-1 remains connected to the source network. |
| Network properties of VM-2 are changed after failover and is disconnected. | VM-1 is disconnected. |
| Network properties of VM-2 are changed after failover and is connected to VMNetwork2-Shanghai. | If VMNetwork2-Shanghai isn't mapped, VM-1 will be disconnected. |
| Network mapping of VMNetwork1-Shanghai is changed. | VM-1 will be connected to the network now mapped to VMNetwork1-Shanghai. |
Next steps
- Learn about IP addressing after failover to a secondary VMM site.
- Learn about IP addressing after failover to Azure.