Re: WiFi ADSL Modem Router thingy as a Router for a Cable Modem?

On Thu, 11 Aug 2005 09:37:41 GMT, Jeff Gaines commented

> An ADSL Modem/Router that has, say, four ethernet ports will act as a
> dumb switch/router if you just use those 4 ports. If you want the modem
> functions (firewall, NAT etc.) you must plug the 'phone line into a
> specific socket (slightly different socket).

I thought that firewall and NAT were router functions, a router being the
connector between two networks (also known as a gateway) - usually the
Internet and the home LAN, a modem simply converting between transmission
methods - traditionally between the computer bus and audio tones.

A router has two IP addresses, one on each network (assuming it is connected
to just two networks, and both use Internet Protocol - usual but not
meccessary)

However, having checked with http://www.webopedia.com, it seems that NAT &
firewall are functions of yet another box, which some manufacturers happen to
combine with a router.

A switch is a device that filters and forwards packets between LAN segments -
in a small network, each segment will have just one host (computer, etc) on
it, so the packet travels only over the segments with the originating and
target hosts on, as opposed to an unswitched hub, where the packet will be
forwarded to all attached segments.

So a typical ADSL Modem/Router contains an ADSL modem, a Router, a NAT box,
and a switch. The modem converts the signal from the ADSL line to something
the router can handle; the routers uses headers and forwarding tables to
determine the best path for forwarding the packets, and uses protocols such
as ICMP to communicate with other routers and configure the best route
between any two hosts; the NAT box makes all necessary IP address
translations; and the switch selects which ethernet port, and hence which
host, the packet is to be forwarded to. This is for inbound packets, outbound
go in the reverse direction, and have reverse conversions.

Having written (or pasted) that, and remembering that the four functions are
typically packed into a single box, I'm not surprised that there is confusion
and confuzzlement.

To do what pmj wants, the box would need a further ethernet post, connected
on the WAN side of the router, in parallel with the connection from the
modem.

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