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I have set up 2 separate wired LANs each one with its own DSL connection. Each LAN consists of the ISP's residential DSL modem, a switch and some PCs, NAS, media players etc. What I want is to connect the 2 LANs while each one is keeping its own internet connection but seeing each other.

Is it possible? How can it be done?


Thank you everyone for your prompt reply. Just to clarify what is my need. Each LAN has its own DSL legal connection and telephone numbers. Physically there are two different apartments but it is able to run a cable from one to another. So each one of two modem router creates a LAN. I need to see other LAN's PCs, and network devices but each LAN maintain separate internet connection (thus telephone etc). I dont want file sharing over internet VLAN etc

I wonder if i: Run a UTP crossover cable from one ISP modem/router to the other connecting to LAN ports. Configure each DHCP server with different IP like A: 192.168.2-10 and B:192.168.2.12-20 Set manually on each PC and network device the IP manually Configure each modem/router other setting the same on both routers

Will this work?

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Basically you have two local networks in the same space, but you want half of the computers to use the Internet #1 and the other half to use the Internet #2. Is that correct? –  Havenard Apr 3 '13 at 18:19
    
It could be done but I would not recommend it as there are so many things that you could screw up. You would have to correctly configure every single device in the network, the clients with the right IP, netmask, default gateway, DNS, ... and the routers with the routing. So my advice is to invest some money rather than a lot of time... But in the end its your call ;-) –  Simon Apr 3 '13 at 18:23
    
Invest some money in equipment? technical service? –  elpa Apr 4 '13 at 7:16

3 Answers 3

Yes it is possible.

First of all, you have to make sure that the two networks are in different subnets like:

192.168.1.0/24 for network A and 192.168.2.0/24 for network B

Than you would have to connect the two subnets. That can be done by using two routers.

  • Router A would be connected to network A via the LAN port and to network B via the WAN port.
  • Router B would be connected to network B via the LAN port and to network A via the WAN port.

The routers would have to be configured properly so they know which network they are serving and which packets they should forward.


As requested by YLearn I explain the solution a bit more detailed:

Router A and B are additional devices and work as DHCP server in their network. The existing DSL modems would acquire a static IP of those routers. The routers could be configured as follows:

  • Router A:
    • assign IP 192.168.1.100 to the DSL modem
    • send the traffic for 192.168.2.0/24 to the WAN port
    • send the internet traffic (unknown IP) to 192.168.1.100


  • Router B:
    • assign IP 192.168.2.100 to the DSL modem
    • send the traffic for 192.168.1.0/24 to the WAN port
    • send the internet traffic (unknown IP) to 192.168.2.100
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As I said "The routers would have to be configured properly"! That means that the routing tables have to be set to not contain loops. With such a simple setup it is not that hard to do. –  Simon Apr 3 '13 at 16:00
    
I think this requires two additional routers or routers with three interfaces (e.g. dual WAN). Routing schemes aside, without them, there would not even be a socket available for you to physically connect the DSL modems to. –  Marcks Thomas Apr 3 '13 at 16:47
    
@MarcksThomas you are right, the two routers I mentioned are two additional routers. –  Simon Apr 3 '13 at 18:01
    
@Simon, thank you for the clarification. Looks good now, so I will go ahead and delete my other two comments. I do however prefer my posted setup as it allows for LAN1 to go out GW2 (or vice versa) if needed with only a routing change. –  YLearn Apr 3 '13 at 19:00

That pretty much depends on what is coming out of these 2 outlets:

So you have two independent legal Broadband accounts (can be two DSL two Cable or one of each.)

There are two terms that might be associated with using two independent Internet connections.

  1. Combining Bandwidth.

  2. Load Balancing two connections.

Let assume that you have two 3Mb/sec. connections each capable to download at 300KB/sec.

With Combined Bandwidth you should be able to download one file at 600KB/sec.

With Load Balancing one single file will not exceed download speed of 300KB/sec. However you can download 2 files at 300KB/sec. or 4 files at 150KB/sec. etc.

Unfortunately Combining Bandwidth can not be done without the ISP providing such a specific service.

Computers are Not mind readers. If the two connections are not synchronized at the source your computer would know how to combine it to a coherent page.

Any if and but about it is just Wishful thinking.

The price of such a service (if available) is usually much more expensive than upgrading your connection from the basic service to a faster business or corporate service.

If you do have two independent services you can achieve Load Balancing by using a Dual WAN Router.

This type of Cable/DSL Routers have two WAN connections for two Broadband Modems and they would mange the Internet traffic to the LAN to be used in the most efficient way.

The ZyXEL P-663H-51 is such a router.

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Source

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Since I you asked here rather than someplace like http://serverfault.com, I am going to assume you are more of a home user with this special need. To avoid anything complicated, such as policy based routing and VLANs, I will keep the configuration simpler but keep in mind any means of doing what you ask is more complicated than your current setup.

I am going to skip DHCP service configuration, but that can be done on the router or on another device in each LAN. I am also skipping NAT inside the gateway devices; this reduces some complexity, but ultimately adds more and could break some things that don't like to be double NAT'd (once at router and again at gateway to internet).

I also assume that each of the current LANs have a gateway device currently, although these will need to have the ability to set a static route so may need to be replaced. In addition to those two devices, you will want two router devices with at least two Ethernet interfaces where you can configure IP routes. For example, second hand Cisco 2611s will work and be cheap, but may not have the performance you want; you will want to do some research. Alternatively, you could use two Linux servers set up for routing.

I would connect GW1's (gateway device one) WAN port to DSL1, and GW2 to DSL2. Gateways get their WAN IP information from the ISP. On the LAN side, static IPs should be used. For this example, I will say GW1 is using 192.168.0.1 and GW2 is using 192.168.0.2 in the 192.168.0.0/24 network.

Using a switch, connect GW1, GW2, R1 (router 1) and R2 together. Assign R1 192.168.0.3 and R2 192.168.0.4 on the interfaces connected to the gateway devices. R1 would then use network 192.168.1.0/24 for LAN1 and an IP of 192.168.1.1. R2 would use network 192.168.2.0/24 for LAN2 and an IP of 192.168.2.1.

Connect a switch to each of the LAN ports on the routers and hosts within each LAN to their respective switches. LAN1 hosts would use 192.168.1.1 as their default GW, LAN2 hosts would use 192.168.2.1.

On R1, create a static route for 192.168.2.0/24 with the next hop of 192.168.0.4 and default route to 192.168.0.1. On R2 create a static route for 192.168.1.0/24 with the next hop of 192.168.0.3 and default route to 192.168.0.2.

On GW1, you would need a static route to 192.168.1.0/24 with the next hop of 192.168.0.3 and on GW2 you would need a static route to 192.168.2.0/24 with the next hop of 192.168.0.4.

Now your two LANs set up, using their original ISPs, but also able to communicate with each other.

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