Two Routers - 1 Port Straight to First Router

Question

At my house we have two Wifi routers one's connected directly to the modem and the other is plugged in down stairs as a second network(Directly connected to the first router) Is there a way that I could make it so that I have the second router have its own network, but have one or two ports that would act as if they were directly connected to the first router? That way I can port forward to devices on the second router. Here are the information about the routers:

Router 1 - Linksys WRT54G Running stock firmware

Router 2 - Linksys E900 Running Tomato Firmware

So to summarize what I'm asking is how would I have two networks from two routers but be able to connect directly to the first router through one of the ports on the second router.

Here's a Visio Drawing of what I would like to look like

Answer 1

You can use Double NAT. See Double Router Forwarding.

On the first NAT device (Router 1) forward the port(s) you need to the IP address of Router 2's WAN port.

Then on Router 2, forward the same port(s) to the address of the device you need to reach.

See the above link for a more detailed explanation.

Answer 2

No. If Router 2 is functioning as a gateway (i.e., has it's own sub-network), then all client computers will be on that subnet. Router 1 will only ever see Router 2, and to forward ports you would have to configure Router 1 to forward the port to Router 2, and additionally configure Router 2 to forward the port to the appropriate computer (see David's DoubleNAT answer). Other computers on Network 1 will not be able to see a computer on Network 2 directly

The only way that a computer can be physically connected to Router 2 and interacted with as if it's in Router 1's network is if Router 2 is functioning as a bridge/switch (Tomato supports this, IIRC). In this situation, there will be no separate network for Router 2.