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Please forgive my ignorance, but I need to set up an IPSEC site-to-site VPN between our 192.168.x.* network and a 10.y.z.* network somewhere else. I guess I need some appliance that can masquerade the 192.168.x.* packets as 10.y.z.* packets and vice versa. Can this be accomplished via source NAT? Do I even need source NAT?

Right now we have a Cisco RV320 router which can do site-to-site VPNs but not source NAT (it does PAT but it looks to me like that doesn't include source NAT).

What's the easiest way of accomplishing this?

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    Are you sure you need to NAT? Since your addresses don't overlap, you probably don't need it. – Ron Trunk Sep 19 '17 at 13:42
  • I'd love to do this without NAT but I don't see a straightforward way to do it on the RV320. The problem is that the address range we use on our end (192.168.x.*) is occupied at the other end, so I need to somehow map it to 10.y.z.* which they're not using. – user12345 Sep 19 '17 at 14:02
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    Can you be more specific about which address ranges are used in which location? – Ron Trunk Sep 19 '17 at 14:10
  • NAT is not needed with different address ranges as you have outlined in your question. By the way, that route does do inside-source NAT. – Ron Maupin Sep 19 '17 at 14:31
  • Okay, that's good to know. So I have all the hardware I need, I just need to figure out how to set it up. – user12345 Sep 19 '17 at 14:36
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This does happen a bit to have duplicate subnets when trying to setup a vpn. Use your favourite web search engine to search for "site to site vpn with duplicate subnets"

For example: https://learningnetwork.cisco.com/thread/66026

The RV320 is a nice SOHO router and performs well for a small business. Please let us know how you go with your set-up.

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Since the private IP addresses on both sides don't overlap there's no need for NAT. Bear in mind that NAT is a kludge and should be avoided where possible.

When you establish a VPN tunnel you need each side to know that the other side's subnet is reached through the tunnel. The easiest way is to set up the static routes 192.168.x.0/24 -> tunnel interface and 10.x.y.0/24 -> tunnel on the far side.

When the default gateway on each side differs from the VPN gateway you also need to add the route on that.

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