Double NAT/Twice NAT VPN Setup

Please help with configuration of a Double NAT VPN

Diagram of the VPN Network
Client A has a Site to Site VPN to Client B
Client A will soon have a Vlan in it's network to Client C
Client A and C have the same Subnet, and changing them is non optional. (

I need to reconfigure the VPN so that there is no longer a conflict.

Client A will send traffic to new remote network
Client B will NAT traffic from to and Vica-versa on it's way back to Client A

Client B is running Cisco ASA 8.2
Client A is running a Sonicwall TZ210 (or similar)

I need assistance with configurations for the Cisco ASA... I speculate the Sonicwall will just update the remote network details for IPSec.
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Daniel HelgenbergerCommented:
please have a look on this recent (ongoing) thread:

Exactly the same. The consensus so far is not to use the quite complicated dual FW setup any more but one next gen firewall.

But your question is answerd here:
Jan SpringerCommented:
When connecting two internal networks on the same subnet via a VPN, perform NAT through the VPN tunnel so that the conversation between the two networks is: public network to private network.
QlemoBatchelor, Developer and EE Topic AdvisorCommented:
The SonicWall just needs to NAT to, forcing to the VPN tunnel. The answers come back from, and are translated to again if arriving via the tunnel.
Packets from/to on A/C network will not get translated.

That way, nothing has to be done on the ASA side, only SonicWall needs to perform destination NAT.

Here a guide for VPN with overlapping networks. But you would need to configure NAT on the Sonicwall as well

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Blue Street TechLast KnightCommented:
Any update on this?
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