In order to setup the Tomato Firmware router as an access point, the following steps have to be completed. This is a setup for a home environment. If you are setting this up for a workplace, the IP address range should be something other than 192.168.1.1 (as it is too common). Same goes for the Subnet, it should be something other than 255.255.255.0, if you need more than 254 IPs.
Disable WAN/Internet (set to "disabled")
Setup the access point IP address to something other than the main router (Eg: if the main router is 192.168.1.1, then set the access point to 192.168.1.2 or similar)
Subnet Mask should be set to 255.255.255.00
Set "Gateway" to the IP address of the main router (Eg: if the main router is 192.168.1.1, then that will be the gateway)
Under Advanced - > DHCP/DNS check "Use user-entered gateway if WAN is disabled"
Disable DHCP
Enable wireless and configure the security. Set wireless mode to Access Point.
Connect a cable to one of the LAN ports. Although you can re-use the WAN port as additional LAN port when WAN is disabled, it is recommended to use one of the LAN ports to avoid confusion.
