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GNU/Linux Desktop Survival Guide
by Graham Williams

Router to Router Connections

Suppose we have a typical ADSL modem with a four port router (e.g., a Fritz!Box 7390 (as of January 2012), an iiNet Bob2 (failed to get it working stably for 8 months from July 2011 and provider gave up trying to help and refunded it), or a 2Wire 2701HGV-W, or a D-Link DSL504 ADSL Modem/Router). We've bought (or have lying around) a second router (e.g., a Belkin 54Mbps Wireless 802.11g) and want to use this to add more computers to the network through ethernet cables to share drives, printers and the Internet connection. Let's refer to the first ADSL router as router A and the second as router B.

Optional: We probably don't need to limit the DHCP address range on router A--just as long as the address we use for router B has not been allocated to some other computer by router A, but my instructions used to include the following suggestion: Configure router A to issue DHCP addresses in some range that does not include one IP address that we will use for router B. For example, we might configure router A to only issue IP's in the range starting at (or or and ending at (or or Then we'll configure router B with (or or This is all the setup that is required for router A, which otherwise has DHCP enabled and its usual WAN (ADSL) setup for your ISP.

Disable DHCP for router B (and perhaps we don't need the router's firewall or DMZ), and configure its WAN (Wide Area Network) type to be STATIC and set it to any IP (e.g., or should be different to the A network), with a netmask of Specify a gateway IP of (or perhaps or, if your router will not allow This will stop it sending traffic to its WAN (we won't be using this router's WAN connection).

With the LAN (local area network) configuration for router B set to STATIC set an IP address within the subnet range of router A but outside its DHCP range. We might set the LAN IP to (or or with a Subnet Mask of (or perhaps if that doesn't work) and with DHCP Disabled. Router A will serve as the DHCP server for anything connected to router B.

Make sure that nothing is plugged into router B's WAN. Connect a LAN ethernet port of router B to a LAN ethernet port of router A to have them talking to each other, using the usual ethernet cable that you would use to plug your computer into the router. The setup will look something like the following:

   Router A                     Router B
   WAN: --> ISP modem           WAN: Empty ethernet
        Configured for ISP           Static IP with Gateway
   LAN:                         LAN:
     IP=                  IP=
     Subnet         Subnet
     DHCP: Enabled                DHCP: Disabled
   LAN Ethernet Cabling:
     (1) <======================> (1)
     (2) --> PC1                  (2) --> PC4
     (3) --> PC2                  (3) --> PC5
     (4) --> PC3                  (4) --> PC6

That's it! (But check out Section 69.4.5 for details on protecting your wireless connection from random access.)

Now, computers serviced by router B (directly connected by Ethernet cable or else connected wirelessly) will be assigned DHCP by router A, within the 10.1.1.* (or 192.168.0.*) network, together with DNS assignments. Router B is just another IP node on A's network. Any LAN computer can access and configure router B by accessing it as (or All computers will be on the same network subnet and so they will have access to each other for file and printer sharing.

I added [110421] another old router (replaced D-Link ADSL) as router C. It's network address was set to (or It is connected directly through to router A. Remember to disable DHCP for router C. This seemed to function without further setup.

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