Networking: How to add another router

[Nadav Har'El]

On Sun, Feb 13, 2011, Geoff Shang wrote about "Networking: How to add another router":
> I find myself with the need to connect 5 ethernet devices to 4 available 
> ports.
>...
> to help solve my problem.  The closest I've seen is a way to send two 
> 10/100 mbps Ethernet feeds down the one ethernet cable, but you still need 
> two ports at each end.  I only have one so that's no good.

Your problem is trivially solved by the addition of any modern switch, or
even ancient hub.

You connect 2 of the devices to the switch, and connect the switch with one
wire to the 4th available port.

All modern switches (and this probably includes your home router) learn MAC
addresses they see on input ports, and there is no limit to one MAC address to 
one input port. In other words, your router learns by watching the traffic
that your two computers' MAC addresses are both located on the end of one
port (behind the switch, but it doesn't know that), and switches packets
for these MAC addresses to this port. ARP traffic (to find the layer-2
MAC address of a layer-3 IP address) is duplicated to all ports, giving a
chance to all computers, not just 4, to answer.

In any case, a switch works on layer-2: MAC addresses and Ethernet packets.
You can still have a flat layer-3 network (one subnet) on top of a whole
tree of switches, hubs, and the likes.

So basically, you have a non-problem: the wire splitting device you were
looking for is any switch or hub you can lay your hands on.

Nadav.

-- 
Nadav Har'El                        |      Sunday, Feb 13 2011, 10 Adar I 5771
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