Asus RT-N12, DD-WRT v24-sp2 build 14896 (08/07/10), mini image (4MB firmware size), connected to the internet, later being referred to as Router 1.

TP-Link TL-WR1043ND, same version, regular firwmare (8MB), later Router 2.

Despite routers run on Broadcom and Atheros chips, it was possible to configure them to cooperate. Both internet and local network are now working.

Setup - Router 1
WAN Connection Type = Automatic configuration - DHCP.
Local IP Address = 192.168.1.1/255.255.255.0
Gateway = 0.0.0.0
Local DNS = 0.0.0.0
DHCP server is enabled, Start IP Address = 192.168.1.100.

Setup - Router 2
WAN Connection Type = Disabled.
Local IP Address = 192.168.1.2/255.255.255.0
Gateway = 192.168.1.1 (Router 1)
Local DNS = 192.168.1.1 (Router 1)
DHCP server is disabled.

Setup - Advanced Routing, operating mode:
Gateway (Router 1)
Router (Router 2), LAN & WAN (LAN would probably work too, since WAN is disabled).

Security: WPA2 Personal using AES.
WDS is not used in any way.
Wireless basics:
Router 1 = AP, Router 2 = Client Bridge,
Network Mode = Mixed,
Wireless Channel is fixed (I used ch.4),
Wireless SSID Broadcast = Enable
Channel Width = 20MHz,
Network Configuration = bridged.
Advanced Wireless Settings. Preamble = Short (read in some article on the net, not sure if it’s needed or not).
I am only using 1 physical wireless interface on both routers for this setup, no virtual ones.

Status -> Wireless -> Site survey to Join a network. Does not ask for a password, will use the configuration on Wireless pages.

On Windows 7 Network Map, PCs from Router 2 network appear connected through a Bridge, as opposed to Switch for devices on Router 1 network.

A quick tip for those new to Linux and struggling to access their DD-WRT router over Telnet. If you changed the username during its first startup, it was only changed for web access, linux/DD-WRT login is always root. Password = the one you entered. I only used Telnet to test internet access, i.e ping by IP (routing check) and host name (DNS check).