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How to configure 2 routers on the same local network

January 18th, 2007 ericdes

Many have reported problems trying to put 2 routers on the same LAN. While router R1 remains connected to the internet and working fine, your idea is to plug another router R2 to it.

I will write about several configurations in this article. While options 1 and 2 will sound familiar to many of you and unfortunately inconvenient as the same time, you might want to give your preference to the 3rd option which offers some of the best of both worlds…

Option 1 - Router R2 as a switch

A first approach is to daisy-chain R2 to R1, i.e. you attach a cable from one of the free LAN ports on R1 to one of the free LAN ports on R2. Whatever you set in the configuration of the router R2 won’t matter because it will downgrade as a regular switch. A DHCP server running on R1 will propagate its service to the computers connected to the R2 ports as well.

It’s clear that approach is fine if you have a new router with new features that include the ones from your older router. In that case, install the new router as R1 and the old one now R2 as a switch — you will save on a new switch should you need more ports although switches are now very cheap and use much more electricity than routers.

Option 2 - Router 2 as a router

It’s definitively worth trying to attach your cable to the WAN port of router R2. Computers attached to R1 will be able to use the features provided by R1 whereas those connected to R2 will get the features available on R2.

You will also discover a computer connected to R1 won’t ’see’ a computer connected to R2, and vice-versa. Forget about sharing the same LAN, even if both routers set their LAN with the same range of IP addresses, computers will remain invisible to those connected to the other router. You will end up with 2 LANs instead of one.

I’ve read many posts in forums about running a DHCP server on the first router while leaving the second DHCP server disabled, adding a static route between both routers. Actually none of this has ever worked for me.

I came up with this 3rd solution which actually solved my problems.

Option 3 - A better solution

In this scheme Router R1 which is connected to the internet now is in charge of supplying an internet socket to R2. This means R2 will see R1 as the internet gateway and won’t expect any more from it.

We’ll set R1 with IP 192.168.0.1 and DHCP disabled. Connect a cable from a free LAN port to the WAN port of router R2.

Now set the internet connection of R2 as a static IP address with the value of R1: IP 192.168.0.1, Netmask 255.255.255.0 / Gateway 192.168.0.1.

That configuration alone should bring internet to R2. Now we want R2 to act as LAN and DHCP server. Let’s put its IP address to 192.168.0.201 (an example) with its LAN network 192.168.0.0 of netmask 255.255.255.0, the DHCP server starting with IP 192.168.0.2.

Now every device connected to a LAN port on R2 will share that network. If you attach another cable from a LAN port on R2 to a LAN port on R1, R1 will now act as a switch for R2. Therefore the DHCP on R2 will service the computers attached on R1, each computer will ’see’ each other. We’ve solved the problems encountered in option 2.

So we’ll have Internet -> Router R1 (router mode) -> Router R2 (main router) -> Router R1 (switch). You’ll able to use some router features on R1 (before the packets arrive to R2 and after they are sent from R2) as well as those on R2. We’ve solved the problems encountered in option 1.

When booting you LAN, start with R1 and see that your computers won’t get an IP address from R1. Start R2 and see that it gets an internet connection. Renew the addresses on the computers connected on R1 and see how the DHCP on R2 responds. As a matter of fact you’d rather start your LAN by turning router R1 first then R2.

My setup

My router R1 is a SMC Barricade with a DSL modem.
I received a Linksys router (R2) from Vonage which I needed to include in the network.

The SMC is the router (IP address 192.168.0.201) connected to the internet and supplies internet to the Linksys router through its WAN port.

In the Linksys router I had to forward the ports 10000-20000 to 192.168.0.201 because Vonage requests them open for outgoing traffic.

Whether a computer is connected to the Linksys or SMC routers they are able to ping each others.

As an added bonus it works as Vonage recommends it: the Linksys router is installed before any other routers as it is Qos enabled and gives priority to the voice. This is possible because all computers whether attached to it or the SMC router are now behind it.

The SMC is Wifi enabled which is not the case for the Linksys router. As a consequence, a computer connected wirelessly won’t go through the Linksys router, and won’t be part of its network. It gets connected to the internet directly from the SMC router. As you might have expected it the Wifi might be the only feature on R1 not available on the LAN.

Entry Filed under: Networking