How can I configure NAT over VPN in a Site to Site VPN?
03/26/2020 
1669 
57630
DESCRIPTION:
A VPN tunnel cannot be established if both the destination network and the local network have the same subnets. The Apply NAT Policies feature or NAT over VPN is configured when both sides of a proposed site to site VPN configuration have identical, and hence overlapping, subnets.
Network Setup:
In this scenario, a VPN tunnel is created between a SonicWall NSA 2650 and a SonicWall NSA 4600, and NAT over VPN tunnel is configured to translate the networks to a different subnet. Site A subnet, 192.168.1.0/24 is translated to a virtual subnet of 172.16.1.0/24 and Site B subnet, 192.168.1.0/24 is translated to a virtual subnet of 172.16.2.0/24.
- Site A: 192.168.1.0 /24 is mapped to 172.16.1.0 /24
- Site B: 192.168.1.0 /24 is mapped to 172.16.2.0 /24
RESOLUTION:
Configuring Site A (NSA 2650)
Create Address Object for Local & Remote Network
- Login to your SonicWall management page and click Manage tab on top of the page.
- Navigate to Objects | Address Objects page. On right side, click Address objects tab and select View as Custom.
- Click Add button under Address Objects, to get Add Address Object Window.
- Create an Address Object called Local Translated. This is the NAT'ed network for the local subnet.
- Name: Local Translated
- Zone: LAN
- Network: 172.16.1.0
- Netmask: 255.255.255.0 (This is required to be identical to the actual local subnets)
- Create an Address Object called "Remote Translated". This is the NAT'ed network for the remote subnet.
- Name: Remote Translated
- Zone: VPN
- Network: 172.16.2.0
- Netmask: 255.255.255.0 (This is required to be identical to the actual remote subnets)
Create VPN Policy
- Login to your SonicWall management page and click Manage tab on top of the page.
- Navigate to VPN | Base Settings page.
- Under VPN Policies, click Add button to get VPN Policy window.
- Create a new Site to Site VPN policy with settings as per the screenshot.
Configuring Site B (NSA 4600)
Create Address Object for Local & Remote Network
- Login to your SonicWall management page and click Manage tab on top of the page.
- Navigate to Objects | Address Objects page. On right Side, Click Address objects tab and select view as Custom.
- Click Add button under Address Objects, to get Add Address Object window.
- Create an Address Object called Local Translated. This is the NAT'ed network for the local subnet.
- Name: Local Translated
- Zone: LAN
- Network: 172.16.2.0
- Netmask: 255.255.255.0 (This is required to be identical to the actual local subnets)
- Create an Address Object called "Remote Translated". This is the NAT'ed network for the remote subnet.
- Name: Remote Translated
- Zone: VPN
- Network: 172.16.1.0
- Netmask: 255.255.255.0 (This is required to be identical to the actual remote subnets)
Create VPN Policy
- Login to your SonicWall management page and click Manage tab on top of the page.
- Navigate to VPN | Base Settings page.
- Under VPN Policies, click Add button to get VPN Policy window.
- Create a new Site to Site VPN policy with settings as per the screenshot.
- Once both VPN policies are configured with NAT over VPN, the following access rules and NAT Policy would be auto-created.
From VPN to LAN
From LAN to VPN
NAT Policy
How To Test
- Bring the tunnel up by pinging the NAT'ed (translated) ip in the remote site.
EXAMPLE: In order to connect to the web server having IP 192.168.1.100 in Site A from Site B, use the NAT'ed IP of 172.16.1.100. - Likewise, in order to connect to the host IP 192.168.1.5 in Site B from Site A, use the NAT'ed IP of 172.16.2.5.
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