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I have two network with two different ISP. The first network (let say Network A) consist of PCs, Laptops, Printer and NAS. The second network (let say Network B) consist of PCs and Laptops. What I want to do is to join both of the network, so users in Network B can access NAS and printer in Network A. Both of the network have different ISP, and each network should only use their corresponding ISP. Both of the network connected to Asus RT-N66U for wireless devices. So how to connect this two network without each network using other ISP?

the network diagram

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    I feel like you would need to setup up one of the computers in network A as a VPN server. then connect router B (if the router is capable, might have to be each computer) to the VPN server in network A so that all devices in network B will be able to access devices in Network A. Would need to port foward the right ports on router A to the VPN server. Thats my thought on how i may approach it. However Im really keen to see how people do this. – Jason Joslin May 2 '17 at 5:58
  • Are those two networks in the same physical building or are they separate? – Frederik Nielsen May 2 '17 at 6:17
  • Another thought i had was to set up a DNS could be inside or outside network b and configure your router to use it. Set up printer.mycompany.com to point to router As IP address and then set up port fowarding to point the printers port to the printer inside your network. Also within your router you should be able to configure it to only port if request is from the public IP address of router B. Still just a brainstorming suggestion. @esa reckons your router support OpenVpn config so thats probably a better option – Jason Joslin May 2 '17 at 9:10
  • I wouldn't expose the printer and/or the NAS to the public Internet, especially when it is so easy to set up a site-to-site VPN. – Esa Jokinen May 2 '17 at 9:17
  • @EsaJokinen noted thanks for that info :) However if you only allowed from 1 ip address wouldnt it make it okay to be accessible by public? – Jason Joslin May 3 '17 at 3:41
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Luckily, Asus NT-R66U seems to have VPN capabilities. You can configure one ASUSWRT as OpenVPN server and the other as VPN Client.

  • Choose OpenVPN because PPTP isn't secure.
  • The router used as VPN server must have a public IP.
  • Since the other LAN is 192.168.0.0/24 and the other 192.168.1.0/24, it's most likely TUN (tunneling) interface type you want to choose from advanced settings.
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Is there actually a cable running between your two Asus routers? If there is, you don't need to go through the trouble of setting up a VPN between the two devices.

The whole point of a router is connecting disjointed networks. That is literally its only job. We've got used to seeing multiple devices bundled together as "routers", but what you've really got there is a router/firewall/access point/general purpose operating system. We just need to focus on the routing part of it.

I don't know how complicated the operating system on those Asus RT's are, but what you would normally do here is create a tiny network just for the cross-router links, and then tell the router to use that link for accessing the other links.

For example, you would give the router on the left an additional IP address of, say, 192.168.30.1/31 and the router on the right an IP of 192.168.30.2/31

Then you would tell the left router that it can access 192.168.1.0/24 via 192.168.30.2, and you would tell your right router to access 192.168.0.0/24 via 192.168.30.1

The specifics of exactly how to do this I leave to you, as I am not familiar with that device, and from what I can see there are a variety of different operating systems it could be running.

  • After checking the router settings, the closest thing to this is by Lan->Route. But the description tells me that both network can use both of the ISP. LAN - Route This function allows you to add routing rules into RT-N66U. It is useful if you connect several routers behind RT-N66U to share the same connection to the Internet. – Stephen Hadisurja May 2 '17 at 11:29
  • Each network will use its default gateway for every destination that does not have a specific route. So as long as the default gateways are set correctly on each individual network, they will not use the "other" gateway to get out to the internet. Someone could manually force a connection out via the other gateway though, if they really wanted to (this is what a firewall would stop). Adding routing rules is exactly what you want to do, but you need to get the additional IP addresses onto your routers first. – Mark Henderson May 2 '17 at 12:44
  • This is the right way of doing it, creating a VPN is no only unnecessarily overcomplicated and problematic, it will also make the speed between networks really slow as the data will need to get encrypted, sent over the internet from one ISP to the other and then decrypted, encryption and decryption ads considerable load to the routers too. – MrLumute May 3 '17 at 4:10

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