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[Azure] Site-to-site IPSec VPN and overlapping addresses

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#1 Kamil Bielawa

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Posted 30 August 2017 - 04:52 AM

Hi all,


We have following scenario:


Barracuda NGF F-series deployed in Azure in network

Client A office using network

Client B office using network


We need to connect both offices to Azure (so that the offices see Azure, they don't see each other). That would be quite simple without overlapping address space, but how can we solve it with the overlap?

#2 Steve Vickers

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Posted 31 August 2017 - 02:28 AM



you can do this using a Map Rule and Translation Map for one or both destination networks:





#3 Alex Creech

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Posted 02 September 2017 - 06:56 AM

Could someone provide a recipe\example for this scenario? Azure would need user defined routes and network securty groups setup also, right?

#4 A. Remili

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Posted 26 September 2017 - 11:19 AM



I am also interested in the process if anyone has a recipe lol



#5 Bartek Moczulski

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Posted 11 October 2017 - 03:49 AM

The missing bit of information here is that you need address translation on the branch office boxes (assuming you have them). So the recipe (with example subnets) is:


on Branch A Box:

- firewall rule passing traffic from to Azure and mapping source (using translation map) to

- VPN to Azure with local network


on Branch B box:

- firewall rule passing traffic from to Azure and mapping source (using translation map) to

- VPN to Azure with local network


on Azure box:

- pass traffic from and with Dynamic SNAT


downside: Azure boxes do not see original client IP, neither port. You can optionally map the source back to on the Azure box firewall (+set UDR in Azure to send data towards via NGF box). Remember, if setting UDR, NGF needs to be in a different subnet than your Azure resources.

#6 Kiran Bheemarti

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Posted 28 November 2018 - 06:47 PM



How can we achieve the same without NAT on BranchA and BranchB boxes.


My scenario is similar


OnPrem1 (

OnPrem2 (


Azure VNet (


Installed Barracuda F-Series in Azure VNet. 


I need to set up site-2-site tunnels from OnPrem1 to Azure and OnPrem2 to Azure, but I don't have control on OnPrem1 and OnPrem2 routers, adding NAT rules is not an option. 


How can I achieve this overlapping address space site-2-site topology?