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I am not a network specialist by trade, and I learn largely by trial and error after working here for 2 years. What I am trying to do now is set up the link between X and Z, figuring out the values in red so that clients and servers behind Z can use internet through X.

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Our existing network consists of Y and Z working properly. We also have a VPN trunk established through this link. I am now trying to set up X.

X came to me with LAN IP: with DHCP. However, my clients and servers are actually on 192.168.3.*. After extensive reading, I came up with the values in RED. But it never worked for me.

Can I verify, theoretically, whether the setup above should work? If not, what is wrong? Is there an easier or more straight forward configuration to use?

Also, Z (DrayTek 3900) acts as a VPN server for client incoming connections and also maintains another VPN trunk to a remote site. In this case, would it be easier to just always static route X to Z?

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Can you get this to work, yes. With the equipment and software you've got, probably not, at least not the way you'd want it to work (I'm assuming you want to use 4G as a "backup" for your Internet connection). What is Z? Setup's like this really aren't "straight forward" at all... unless you simply buy a device that does it for you (easy, cheap, timely - pick two, and all that). – Chris S Jul 31 '13 at 4:24
Have a look at Zeroshell this might be useful. – vasco.debian Jul 31 '13 at 4:35
Sorry, Z is a DrayTek 3900. It supports Dual WAN and also HA. So, given that Z supports it, is the configuration correct? – Jake Jul 31 '13 at 7:58
up vote 1 down vote accepted

It looks to me like you are trying to setup a dual wan connection to the internet. Connection Y being your isp fiber connection, and X being your 4g internet connection. I have done several dual wan setups almost exactly like this. It can be done. But Z needs to be a dual wan capable router, supporting either load balancing (sharing the bandwidth across both connections) or using wan2 as a failover backup wan (wan1 goes down, wan2 comes up). It will not work if your router does not support dual wan. Here is the dual wan router I used for a small business in remote Alaska that had a dsl connection to the isp, and a satellite as backup:

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Sorry, Z is a DrayTek 3900. What I want to know is whether the IP and subnet configuration should actually work. – Jake Jul 31 '13 at 8:00
Yes that ip config should work. Your gateway is and the wan ip of should connect to X that way. – Ben Jul 31 '13 at 17:05

The setup looks fine, assuming dual WAN is properly configured on the DrayTek. You'll have dual NAT to the 4G LTE network, but those typically don't support the kinds of things that dual NAT breaks anyway.

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The mask /22 for your X IP address is odd. I guess you meant to include the 192.168.3.x addresses with that but that wont work. Your mask must be /24 in all 192.168.1.x nodes. Next to this, set portforwarding from X towards for anything that you want to be able to access the 192.168.3 net from the Internet (in your case in particular the VPN). If possible with your equipment, define as a DMZ host in your X router. That will forward anything to it by default and is by far the easiest solution.

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Huh? You can subnet RFC1918 address ranges however you want - the constraint is that all nodes in a subnet have to have the same netmask (and network number), so that there is a return path (among other reasons). Also, this "DMZ" thing typically exists only on consumer-level hardware... – Falcon Momot Oct 16 '13 at 14:13

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