Add a second Router to your LAN


By: Curt R
August 28, 2009

We have many requests in the Network Forum on how to properly add a second (or third) router to an existing LAN that already has a SOHO router connected to the internet.  I'm going to write out a brief guide so the next time it comes up, I can just post a link to this instead of typing it all out again!

The general setup of SOHO Router's is similar.  While some use a different subnet, every one I've worked with uses a Class C Private IP Addressing Scheme.  I'm going to use the basic Class C private for this tutorial (192.168.0.0)

I'm going to give two setup guides:

Version 1 will be for a simple, single subnet setup

Version 2 will be cover separate subnets

The term “Router1” will refer to the router connected to the internet.  Any others (ie: Router2, Router3) will be downstream of Router1

Version 1:
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When connecting a second router to an existing LAN it’s easiest to connect LAN port to LAN port and configure the LAN side of the downstream router as compared to connecting to the WAN side.

Router1 (LAN Side):
IP: 192.168.0.1
SM: 255.255.255.0
DHCP Enabled = Yes
DHCP Scope: 192.168.0.100 to 192.168.0.199

Router2 (LAN Side):
IP: 192.168.0.2
SM: 255.255.255.0
Default Gateway: 192.168.0.1
DHCP Enabled = No

You will note in the above configuration that the LAN IP of Router2 is within the same subnet as Router1 but is outside of the DHCP Scope defined on Router1.  This is important.  If you use an IP within the scope, the DHCP service may attempt to give that IP to another computer you plug into your network.  Using an IP outside of the scope avoids this potential problem.  Also, devices like Routers, Servers, network printers should always have a statically assigned IP address so that the IP never changes.

If you have everything configured correctly, any computer plugged into Router2 will get an IP from the DHCP service on Router1 and will have full LAN and internet connectivity.

The DHCP Scope’s Default Gateway IP address should point at Router1 (192.168.0.1) as it is the gateway to the internet.

If you need to add another router, or two or three, simply set the LAN IP on Router3 to 192.168.0.3 and configure all other TCP/IP settings the same as Router2.  Do the same for any others you may add.  I would like to point out, using a switch makes more sense than using a router as a switch requires no setup. 

Version 2:
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When you wish to have a separate, and secure, LAN attached to your existing network you will need to segregate the new LAN using a different, and separate subnet. In order to do this, and provide internet connectivity to the new LAN, you will need to configure your downstream router (Router2) and use routing to go between subnets. In this case, you will use the WAN port on Router2 to connect to the upstream router (Router1).


Router1 (LAN Side):
IP: 192.168.0.1
SM: 255.255.255.0
DHCP Enabled = Yes
DHCP Scope: 192.168.0.100 to 192.168.0.199

Router2 (WAN Side):
IP: 192.168.0.2
SM: 255.255.255.0
Default Gateway: 192.168.0.1

Router2 (LAN Side):
IP: 192.168.1.1
SM: 255.255.255.0
DHCP Enabled = Yes
DHCP Scope: 192.168.1.100 to 192.168.1.199

Every SOHO Router I’ve setup like this configured the route between subnets automatically when both the WAN and LAN side are configured correctly. It’s simple enough to find out if it’s working, plug a PC into a LAN port on Router2, if you can access the internet, it’s working. If you can’t, you may need to check the routing table to ensure you have the route between the two subnets (WAN and LAN side) properly configured.

Once setup and working properly, the 192.168.1.0/24 LAN will have internet access, connectivity with anything else plugged into Router2, and will have access to anything plugged in to Router1.

Computers plugged into Router1 will have internet access and LAN access to devices plugged into Router1. But they will not have access to anything plugged into Router2.

If you wish to let clients plugged into Router1 have access to the subnet on Router2, you would have to add a static route on it (Router 1) that points at the Router2 gateway IP address. Although I want to add, in most cases, you use this method to separate the two. It’s much easier to use Version 1 if you want full sharing between the clients plugged into the two routers.


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