How to configure NAT over VPN in a site to site VPN with overlapping networks


To watch a video tutorial on this topic, click here
 


Feature/Application:

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.

Procedure: 

In this scenario, a VPN tunnel is created between a SonicWALL NSA 2400 and a SonicWALL NSA 240, 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

Configuring Site A (NSA 2400):

Step  1. Login to the SonicWALL Management interface.
Step  2. Navigate to the Network > Address Objects page.
Step  3. 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)

Step  4. 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)

Step  5. Navigate to the VPN > Settings page.
Step  6. Click on Add to create a new Site to Site VPN policy with settings as per the screenshot.

Configuring Site B (NSA 240):

Step  1. Login to the SonicWALL Management interface.
Step  2. Navigate to the Network > Address Objects page.
Step  3. 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)

Step  4. 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)

Step  5. Navigate to the VPN > Settings page.
Step  6. Click on Add to 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:

 

 


How To Test:

Bring the tunnel up by pinging the NAT'ed (translated) ip in the remote site.
For eg. 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.