Router to Router Connections

Suppose you have an ADSL modem with a four port router (e.g., a D-Link
DSL504 ADSL Modem/Router). You've bought a second router (e.g., a
Belkin 54Mbps Wireless 802.11g) and want to plug this into the
network to add in and to share more local machines, and to share the
Internet connection. Let's refer to the first ADSL router as router
A and the second as router B.

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, router A might only issue IP's in the range
starting at 192.168.0.2 and ending at 192.168.0.33 and we'll configure
router B with 192.168.0.40. This is all the setup that is
required for router A, which otherwise has DHCP enabled and
its usual WAN setup for your ISP.

Disable DHCP for router B, and configure its WAN
(Wide Area Network) to any STATIC IP. Specify a gateway IP of 0.0.0.0
(or perhaps 192.168.111.1, if your router will not allow
0.0.0.0). This will stop it sending traffic to its WAN (we won't be
using this router's WAN connection). Further configure the WAN Type
to be Static with a WAN IP of 192.168.111.2 perhaps (should be
different to the A network), and a Subnet Mask of
255.255.255.0.

The LAN (local area network) configuration for router
B should be set to STATIC with an IP address within the
subnet range of router A but outside its DHCP range. We might
set the LAN IP to 192.168.0.40 with a Subnet Mask of 255.255.255.255
(or 255.255.255.254 perhaps if that doesn't work) and with DHCP
Disabled. In fact, 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.

   Router A                     Router B
   WAN: --> ISP modem           WAN: Empty ethernet
        Configured for ISP           Static IP with Gateway 0.0.0.0
   LAN:                         LAN:
     IP=192.168.0.1               IP=192.168.0.233
     Subnet 255.255.255.0         Subnet 255.255.255.255
     DHCP: Enabled                DHCP: Disabled
   LAN Ethernet Cabling:
     (1) <======================> (1) --> 
     (2) --> PC1                  (2) --> PC4
     (3) --> PC2                  (3) --> VoIP
     (4) --> PC3                  (4) -->

That's it! (But check out Section 67.3.5 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 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 192.168.0.233. All computers
will be on the same network subnet and so they will have access to
each other for file and printer sharing.