NAT from private address to private address

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tkdimfp

Mar 8, 2018
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Hello, really hoping one of the resident network gurus can point me in the right direction and I hope I am asking this in the right way.

I have a netgear srx5308 router with one Internet WAN connection and then also have a dedicated point to point connection with a 3rd party company plugged into a LAN port. They have assigned me a subnet with only a few addresses. i'll make up some hypotheticals:

192.168.10.x is our local desktop network.
192.168.20.x is our local server network.
192.168.100.x is the server network on the other LAN.
192.168.200.x is the transportation network. i.e. this is a 3 address network for the point to point connection. 192.168.200.1 is the local side and 192.168.200.2 is the 3rd party side.

So, I have a static rule setup for all 192.168.100.x to go to 192.168.200.2, and the 3rd party routes on their side, which is working.

The problem is, they only route back to 192.168.10.x. We need 192.168.20.x to talk to 192.168.200.x as well, but that does not work (there is no route back).

I really cannot control anything on the far side, so I think the best solution overall is to NAT everything going to the point to point connection to 192.168.10.x. Then we can have as many networks as we want on our side and we just need to translate to 192.168.10.x. The question is how can I do this? Or rather, can it be done with the equipment I have? We are also about to pull the trigger on a Meraki device, but functionality seems pretty similar (read: limited).

I think one potential solution is to put the 3rd party connection on the WAN and assign the WAN address to be on the 192.168.10.x network? But I am trying to avoid that since our next device may not have many WAN ports and we want to get redundant Internet.

Thank you in advance!!
 
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I am not sure of the capabilities of your router. The main issue with NAT is the direction the traffic flows. Traffic can easily go from the inside network to the outside network and nat allows the traffic back. The problem comes when the traffic is initiated from the outside network. The router does not know which machine to send this traffic to since all the internal machines she same external IP.

Now if you have a lot of ip addresses you could say nat 1-1 ip like 192.168.1.x to 10.168.1.x. That method mostly except for a apps that detect the ip change.

There are many other variations of nat to pools of ip but if you end up having to assign multiple internal machines to a external IP you will have the issue of...
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tkdimfp

Mar 8, 2018
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those were just as example. the internal addresses are 172.x.x.x addresses.

I am not trying to make 192.168.20.x work directly. Else, every time we setup a new network we will have to get them to make routing changes. Also, there are finite number of addresses.

I am trying to figure out how to translate any internal network address to show as 192.168.10.x to the other side -- essentially the same thing as NATing to a public address, but internally from LAN network to LAN network across a LAN port.
 
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bill001g

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Aug 9, 2012
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I am not sure of the capabilities of your router. The main issue with NAT is the direction the traffic flows. Traffic can easily go from the inside network to the outside network and nat allows the traffic back. The problem comes when the traffic is initiated from the outside network. The router does not know which machine to send this traffic to since all the internal machines she same external IP.

Now if you have a lot of ip addresses you could say nat 1-1 ip like 192.168.1.x to 10.168.1.x. That method mostly except for a apps that detect the ip change.

There are many other variations of nat to pools of ip but if you end up having to assign multiple internal machines to a external IP you will have the issue of traffic only working when it is initiated from the inside network.

Of course none of this is supported by most consumer grade routers they allow only a simple nat to a single IP. Commercial equipment and even many third party firmware for consumer routers support very advanced nat configurations.

Mostly your issue is going to be can you tolerate the restriction sharing ip via nat will impose on incoming connections. If your traffic is always initiated from the local machines then you likely can do what you want IF you get a device that can do more complex nat configurations.
 
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tkdimfp

Mar 8, 2018
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overall, it could not be done with the netgear router. moved to enterprise router.

outside to inside initiated connections managed through port forwarding.

thanks
 
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