First off, I assume this is a simple question, but I do not have a background in networking. Nonetheless, I am responsible for setup and maintenance. I would appreciate any help.

I have the following network layout in one building:

network layout

How do I go about facilitating direct communications between the individual networks? I.e. devices on the VOIP network can communicate with devices on the LAN network without going over the WAN connections? And all devices have access to the DCs and DNS servers located on the network.

The part that confuses me is I need to maintain the WAN separation transparently to the devices. I.e. the stationary phones need to use WAN-1. The stationary desktops need to use WAN-2. The travelling devices need to connect over WAN-3. I am guessing this is achieved by the gateway address passed out by the router dhcp?

Can you recommend any specific cost effective hardware to make this happen for a small user base? Each network uses a Ubiquiti EdgeRouter Lite as the router/gateway if that helps with recommendations.


If your existing WAN routers have extra interfaces then you can connect them to each other and configure either static routes or a routing protocol so those networks can communicate with each other. If the existing WAN routers do not have any additional capacity, then either an additional router with the capability to connect to all of the networks or maybe even better a layer 3 switch that can connect to all the networks and route between them should do it.

If you configured all the existing WAN routers yourself then you can probably do it no problem, you will just want to update the routing tables on the existing WAN routers to have routes to each of the other networks, once you have things all connected.

  • The routers do not have enough spare interfaces. Can you point me towards an appropriate switch? The switch approach sounds plug and play. How do you keep dhcp isolated between networks if they are all plugged together with a switch?
    – user319862
    Apr 5 '15 at 18:29
  • I found an article that goes over using a layer 3 switch. If I understand correctly, I should be able to plug each router and corresponding layer 2 switch into the layer 3 switch and the layer 3 switch can be configured pass dhcp between the router and switch and then route between all of the networks. Any comments about the Netgear M4100-26G switch for this job? The one mentioned in the article cannot be mounted in a rack. Here is the article I mentioned for reference: smallnetbuilder.com/lanwan/lanwan-howto/…
    – user319862
    Apr 5 '15 at 18:58
  • Ouch the the netgear layer 3 switch I mentioned seems expensive. Is that what I should expect one to cost? Maybe you can recommend something that would work for this setup so I do not feel like I am guessing and likely to end up with something that wont offer the needed functionality
    – user319862
    Apr 5 '15 at 19:03

This could easily be achieved with VRFs (Cisco, in combination with route leaking) or policy based routing. Using VRF will give you the performance advantage over policy based routing, but is more complex to configure. My blog[1] has an article on policy based routing and there are plenty of VRF examples on the internet.

[1] https://glennmatthys.wordpress.com/2012/04/24/policy-based-routing-example-route-one-subnet-via-isp-a-and-another-via-isp-b/


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