Asr vnet has same ip address space as main vnet

Question

As you know, when we create azure site recovery, it creates asr-vnet for the target region.

I noticed that asr-vnet has same IP address space with main-vnet. We're also planning to establish VPN connection from on-premise to main-vnet.

My concern is if both Vnets have the same IP address space, does it trigger any IP overlap situations?

Thanks

Answer 1

@tayfun tek

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

I understand that you would like to understand about the address space overlap constraints and best practises in Azure.

From your verbatim,

• I take it that you are planning to connect mainVnet and OnPremises.
• Also, I assume that you are not planning to connect mainVNet and asr-vnet.
• Please let me know if my understanding is incorrect.

Having overlapping address space in a single Network (Azure + OnPrem which are connected) is not a best-practise and is not recommended.

However, since you are planning to connect only mainVnet and OnPremises, I do not see any challenges/scenario where you would end up with an Overlapping Address Range.

Your scenario is illustrated here : Hybrid resources: full failover.

• In the asr-vnet, you only provision gateways but do not establish a connection before failover.
• 
• And After failover, you can delete/disconnect the original connection object and create a new connection with the asr-vnet.
• 

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

P.S:

In case you have a requirement to connect overlapping IP Addresses across Azure S2S, you can consider NAT on VPN Gateway

Thanks,

Kapil

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Answer 2

It does, if the address space matches, it won't be able to be peered:

Your best bet would be to change the address space to the range that doesn't overlap with on-premises and any other network in Azure, to avoid routing issues..

https://learn.microsoft.com/en-us/azure/virtual-network/update-virtual-network-peering-address-space#modify-the-address-range-prefix-of-an-existing-address-range