[CentOS] CentOS or other Linux Internet Router/Gateway

Mon Aug 23 21:32:47 UTC 2010
John R Pierce <pierce at hogranch.com>

> Just to confirm. The Linksys wireless router can become a wireless
> switch with the firewall and router capabilities disabled. (This is a
> Linux version, BTW, so I'm also going to look into the firmware
> modifications, but I doubt I can load my programs there and am a
> little nervous about bricking the router).
>
>

while you still have connectivity to the router do exactly the following 
steps.

A) set the linksys's internet/WAN IP address to a 'safe' static IP, lets 
use 192.168.250.250 ... we'll never use this address.  don't plug 
anything into the WAN port.

B) disable the DHCP and DNS service on the router, and configure the 
linksys LAN IP address to something unused on your 'new' LAN, like 
192.168.0.250 ... you will use this to access the linksys configuration 
web page.

C) setup your new 'nix gateway to talk to your ISP (static, dhcp, or 
PPPoE, depending on the ISP configuration), and the 2nd ethernet as LAN 
address 192.168.0.1, with a dhcp server dishing out a reasonable IP 
range like 192.168.0.100-200.  Also setup a DNS forwarder on the 'nix 
gateway, and set 192.168.0.1 as the DNS address returned by the DHCP 
zone option for DNS.  your clients will use 192.168.0.1 as their gateway 
and DNS, with network mask 255.255.255.0    if you have hosts with 
static IP's you can use any IPs between 192.168.0.2 and 192.168.0.99, 
also 192.168.0.201-254 not counting 250 that we used for the linksys.

D) plug a linksys LAN port into your 'nix gateway, and plug a PC into 
another LAN port on the linksys, and see if its all working.  you should 
be able to raise the linksys config pages as http://192.168.0.250 if you 
used the addresses I gave above.