Question on Azure Site Recovery

Question

Good day. Have question around design/configuring Azure Site Recovery between regions and IP Subnets.

Our current setup is we have a Site-to-Site VPN tunnel between On-Prem and Azure. When reading some documentation, it indicates make the Vnet/Subnets identical in both regions. And then there is some that indicates to make them different because sometimes may run into a routing issue. So I’m curious for those who have setup this up, if you kept the subnets identical in both regions or made them different and why?

 

Thx in advance for any help given.

Answer 1

Hi @Kalel

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

When selecting identical Vnets/Subnets in ASR, there are both advantages and disadvantages to consider:

• It's easier to manage and visualize if your production environment (source) mirrors your DR environment (target). Some applications have hardcoded IP dependencies. Identical subnets can ease the transition during failover.
• If you're on-premises network and your Azure DR network have the same IP subnets, and they're connected via a Site-to-Site VPN, you'll have overlapping IP addresses. This leads to routing issues where traffic doesn't know where to go.

Benefits of selecting different Vnets/Subnets:

• ASR uses network mapping to translate network resources from your source to your target region. This ensures your applications can connect to the right resources after failover, even with different IP addresses. For your reference: https://learn.microsoft.com/en-us/azure/site-recovery/azure-to-azure-network-mapping#:~:text=Based%20on%20the%20target%20you%20select%2C%20Site%20Recovery%20automatically%20creates%20network%20mappings%20from%20the%20source%20to%20target%20region%2C%20and%20from%20the%20target%20to%20source%20region.
• You'll need a way to update DNS records after failover so that your applications and users can reach the failed-over resources in the DR region. Consider using Azure DNS or an on-premises DNS server with dynamic updates. For your reference: https://learn.microsoft.com/en-us/azure/site-recovery/site-recovery-test-failover-to-azure#:~:text=Update%20the%20DNS%20of%20the%20test%20network%20with%20the%20IP%20address%20specified%20for%20the%20DNS%20VM%20in%20Compute%20and%20Network%20settings.%20Read%20test%20failover%20considerations%20for%20Active%20Directory%20for%20more%20details.
• It is better to go with a different subnet in your source and target Azure regions. This avoids IP conflicts and provides a cleaner separation between your production and DR environments.

Kindly let us know if the above helps or you need further assistance on this issue.

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Thanks,

Sai.