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

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.

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 (without providing connectivity between the two  LAN’s) 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).

IP: 192.168.0.1

SM: 255.255.255.0

DHCP Enabled = Yes

DHCP Scope: 192.168.0.100 to 192.168.0.199

IP: 192.168.0.2

SM: 255.255.255.0

Default Gateway: 192.168.0.1

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 but will not have access to anything plugged in to Router1.  The reverse is true also, 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.