Networking: How to add another router

[shimi]

On Sun, Feb 13, 2011 at 6:47 PM, Geoff Shang <geoff at quitelikely.com> wrote:

> Hi,
>
> I find myself with the need to connect 5 ethernet devices to 4 available
> ports.
>
> I'm running an ADSL modem/router with a 192.168.2.x network (for historical
> reasons) and have allocated static addresses to all of the static devices,
> and a pool of DHCP addresses for devices which ask for it.
>
> Right now the fifth device is running on wireless but I want to plug it in
> if I can.
>
> A quick Google tells me that there's no kind of double adaptor available 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.
>
> Assuming that there is no such double adaptor device that I can use to get
> me a fifth port, the only solution I can see is to drag out the Edimax
> router I have here which is no longer being used.
>
> Assuming I do this, I'm wondering how to configure it.
>
> I'm guessing that it will actually have to route.  I can't see myself doing
> bridging because there'll have to be two devices on it (the router will need
> to take up one of the 4 ports on the modem/router so this then leaves 5
> devices and only 3 other ports,).
>
> Presumably I need to configure the WAN port so that it connects to the
> existing network.  Do I need to set aside a subnet of the 192.168.2.x
> network specifically for the second router, or can I just enlarge the entire
> network and have it all just cope, with the right packets going to the right
> places?
>
> My preference would be to be able to keep it all as one big network, as I'd
> rather not have to reallocate static addresses if I can help it, which I'm
> guessing I'd have to do if I had to make the second router have its own
> subnet of the 192.168.2.x network.
>
> Netmasks and such tend to confuse me a little and I'm not sure what I
> should be doing here, so any suggestions would be helpful.
>
>
Take the un-used router; Go into its configuration; Disable the Internal
DHCP server; Verify that the router does not have an IP address which
already belongs to any other device in your LAN (if it does, change it to
something else. best something on a different netmask altogether...);

Then, disconnect one of the devices on your currently active 4 port router;
Connect a cable between the now vacant port to one of the LAN (note: NOT the
WAN!) ports of the un-used router. Then you can use the extra vacant ports
of the previously un-used router as an extension to your existing network.
(The 4 ports in any common router are actually a switch...)

Good luck,

-- Shimi
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