Best way for connecting a new office to the network

Hello,
I have bought two SXT Router for P2P connection and one RB75U-2HnD for local WIFI and wire network.

Yesterday I finished a transparent P2P bridge with WDS over the two SXT devices, that works fine for me. This P2P connects and already working company network to a new office without any network. So to imaging what I mean, it´s like the new office has got a single network-plug connected to the patchpanel and so the main switch of the old network now. Because of the P2P is in transparent mode it´s like if I would have a normal cable connection, so you can forget about the two SXTs.

Now I like to connect the RB75U-2HnD with this new network socket I mounted on the wall, what is connected over P2P with the switch of the old network.
If I use the router in normal AP mode with NAT activated, it works just fine. I´m able to reach the internet an also the computers in the old network.

But out of it´s nature, NAT online allows outgoing requests and I cannot access the new office from the old one.
So what would be the best solutions to connect the RB75U-2HnD with the old network without using NAT, that I can access both network from both sides?
Are there any tutorials on that?

Thank you

for not use NAT, use static routing.

for example, if you have a core router and rb751.


internet---------core router (192.168.1.1/24)----------------(192.168.1.2/24) 751U-2HnD (192.168.2.1/24)------
192.168.1.0/24 192.168.2.0/24

in the core route add a static route like this
ip route add dst-address=192.168.2.0/24 gateway=192.168.2.1


and in the rb751 add a static route like this
ip route add dst-address=0.0.0.0/0 gateway=192.168.1.1