Which Disaster Recovery Test option allows VM failover while retaining the same IP address in the DR region?

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Which Disaster Recovery Test option allows VM failover while retaining the same IP address in the DR region?

Rob McNees 341

I believe the 2 DR Test options are: Test Failover vs a Full Failover. We have done various "Test Failover" drills, but I want to actually bring up the same VM IPs from the Primary Region to the DR Region. This would involve:

Shutting down the Primary region application (Note: I'm doing this test on a QA environment and not the Production Environment )
"Swing" the vNet (Network CIDR) that contains the VMs, from Primary Region to the DR Region. (set peering, route tables, etc to accomplish this)
Perform testing in DR Region
I do NOT want to failback (or "reverse replicate") data during testing back to the Primary Region. All Testing data is throw away. After Testing I want to switch vNet (Network CIDR) back to Primary Region as if nothing happened on the Primary.

Should I do "Test Failover" or "Full Failover" process (to accomplish the 4 points above)? I want the test to be as close as reality as possible without replicating data back to the primary region that was created during the testing itself. Please provide reasons why one over the other (pros/cons) may help me understand. Thank you!

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Answer 1

Naveena Patlolla 4,805 Microsoft External Staff Moderator

Hi Rob McNees

The best way to do a complete testing is full shutdown I.e. failover

1.Please create a different Vnet CIDR from the source, because if you use the same CIDR range there

will be issues in peering, same 2 address ranges cannot peer.

2.The Application which u hosted on the VM it is better join to the domain, and in application use

internal DNS Name instead of using hard coded IP.

3.Once you failover the IP address will change but still your VM name remains the same.

Since you configured with DNS name so they will be no issue.

4.As per best practices source and DR Region CIDR should be different.

But if you want test with same IP address you can test by using test failover option.

Please let me know if you face any challenge here, I can help you to resolve this issue further

Provide your valuable Comments.

Please do not forget to "Accept the answer” and “upvote it” wherever the information provided helps you, this can be beneficial to other community members.it would be greatly appreciated and helpful to others.

Naveena Patlolla 4,805 Reputation points Microsoft External Staff Moderator

2025-07-15T23:21:29.8633333+00:00

Hi Rob McNees

Just want to check if the above answer worked for you or else please let us know if any help, we are always here to help whenever you need us.

Please do not forget to "Accept the answer” and “upvote it” wherever the information provided helps you, this can be beneficial to other community members.it would be greatly appreciated and helpful to others.

Rob McNees 341

thanks Naveen for your reply and attention to detail. Let me address the points and use your enumeration number to reference your comment:

The reason why I want to use same CIDR is because of the following reasons:

         a. I would like to test as close to if we have a real DR and we want to   maintain the same IP number.  Mainly because some applications do not always use DNS and there are so many IP references (not DNS) in other integrating applications that I think this would make it easier on the applications teams (addresses point 2 - yes, I agree it is better to have apps use DNS, but so large, will cause more issues and it is considered best practices, but our network team also wanted to lean to same IP addresses).  

               b.  If we unpeer the CIDR vNets in the primary region, then peer that same CIDR in the DR Region- then there should not be any peering issues (this is what I mean by "swinging the network" to DR Region). if we do this unpeer/peer - do you see an issue if this is done correctly?  Please advise.  But also consider these questions on weighing what is best approach:

Q1: Is moving the peered network from primary to DR Region more of a challenge? "Yes"

Q2: Is this test more of what would happen in a real DR (to move network) "Yes" - so practicing what would actually happen would be preferred. I dont want to have to figure out how to move peering to DR Region in the actual DR event.

Rob McNees 341 Reputation points

2025-07-16T12:54:23.11+00:00
thanks Naveen for your reply and attention to detail. Let me address the points and use your enumeration number to reference your comment: (sorry the first reply I put in a comment!) :-)

The reason why I want to use same CIDR is because of the following reasons: a. I would like to test as close to if we have a real DR and we want to maintain the same IP number. Mainly because some applications do not always use DNS and there are so many IP references (not DNS) in other integrating applications that I think this would make it easier on the applications teams (addresses point 2 - yes, I agree it is better to have apps use DNS, but so large, will cause more issues and it is considered best practices, but our network team also wanted to lean to same IP addresses). b. If we unpeer the CIDR vNets in the primary region, then peer that same CIDR in the DR Region- then there should not be any peering issues (this is what I mean by "swinging the network" to DR Region). if we do this unpeer/peer - do you see an issue if this is done correctly? Please advise. But also consider these questions on weighing what is best approach: Q1: Is moving the peered network from primary to DR Region more of a challenge? "Yes" :-) Q2: Is this test more of what would happen in a real DR (to move network) "Yes" - so practicing what would actually happen would be preferred. I dont want to have to figure out how to move peering to DR Region in the actual DR event.

Thanks again for your thoughtful reply and the help!
Rob McNees 341 Reputation points

2025-07-23T12:35:42.8966667+00:00

@Naveena Patlolla I hope things are well. Please reply to my additional thoughts I posted on July 16th above. Thank you!
Naveena Patlolla 4,805 Reputation points Microsoft External Staff Moderator

2025-07-24T19:47:41.7566667+00:00

Hi Rob McNees
Sorry for the delay in response.
Below are the answers to your questions:
Q1: Is moving the peered network from primary to DR Region more of a challenge? Yes, it's more complex than a simple failover, because we cannot Move Vnet directly, you need to move all VMS in that Vnet.

Q2: Is this test more representative of a real DR event? Yes, It Represents real DR event. The Approach of Unpeer and Peer it will affect anything, so please processed with the Plan you mentioned.

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Which Disaster Recovery Test option allows VM failover while retaining the same IP address in the DR region?

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