Mi router tiene 3 opciones para trabajar:

GateWay:    In this mode, the device is supposed to connect to internet via ADSL/Cable Modem. The NAT is enabled and PCs in LAN ports share the same IP to ISP through WAN port. The connection type can be setup in WAN page by using PPPOE, DHCP client, PPTP client or static IP.

Bridge:      In this mode, all ethernet ports and wireless interface are bridged together and NAT function is disabled. All the WAN related function and firewall are not supported.

Wireless ISP:    In this mode, all ethernet ports are bridged together and the wireless client will connect to ISP access point. The NAT is enabled and PCs in ethernet ports share the same IP to ISP through wireless LAN. You must set the wireless to client mode first and connect to the ISP AP in Site-Survey page. The connection type can be setup in WAN page by using PPPOE, DHCP client, PPTP client or static IP.

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Me parece que el router principal no es muy bueno y se satura muy facilmente al conectarse varios equipos a la vez, me refiero a unos 15 a lo mucho.

Lo que quiero es que el router principal le asigne una IP a mi router y entonces con mi router hacer una RED privada en un segmento distinto para asignar IP a los 2 routers que se conectan a mi, o sea para el router principal es una sola IP o solo equipo.

Que modo seria el adecuado?

Aorita lo tengo en Brigde... y el cable del router principal lo tengo conectado en el puerto WAN.