What does an ADSL modem router switch do with non TCP/IP?

Sorry, but I don't really understand the details of switching and routing.

I want to connect a computer and a printer interface to two of the ports on
a 4 port ADSL modem router. The computer communicates with the printer
interface using ethernet, but does not use TCP/IP (it actually uses
Appletalk). When the switch gets the packets, will it try to look inside
the packets to see where it ought to send the data - if so, it won't find
the TCP/IP info? All that is on the packets is the MAC address - will this
be the MAC address of the printer interface, in which case, will there be
any problem in the fact that the first leg of the journey is actually going
to the MAC address of the switch into which the computer is plugged?

Also, if the switch doesn't really know where to send the packets, will
they also get sent to the router, and hence to the ADSL link? Is this a
potential security problem, or is it not something I need to worry about
because noone is going to be looking for these packets?

(I gather that a hub just connects the ethernet segments without doing
anything to the data, but the devices that are on the market now all seem
to indicate that they are switches, so I understand that these look at the
packets)

Sorry if these questions are couched in the wrong terms, but it just seems
unlikely to me that an ethernet switch that does not know about the
particular protocol in use would be able to send the data to the right
place.

Or am I just worrying unecessarily, (a little knowledge being a dangerous
thing) and it will all just work?

Tim Lyons.

It'll work fine. Switches work on the ethernet layer in the world of MAC
addresses, and are blissfully unaware of IP. They do inspect the
information - called frames not packets at this layer - but routing
decisions are only made on IP data. If the frame doesn't contain IP, the
data stays on the LAN side of the router, with the MAC address used to
decide which port the data goes to.

Cheers, Benedict from ITchest.
--
Add the 'co' to reply
www.itchest.co.uk
Tel: 0870 162 0840

"Tim Lyons" <(E-Mail Removed)> wrote in message
news:timl-(E-Mail Removed)...
> Sorry, but I don't really understand the details of switching and routing.
>
> I want to connect a computer and a printer interface to two of the ports
on
> a 4 port ADSL modem router. The computer communicates with the printer
> interface using ethernet, but does not use TCP/IP (it actually uses
> Appletalk). When the switch gets the packets, will it try to look inside
> the packets to see where it ought to send the data - if so, it won't find
> the TCP/IP info? All that is on the packets is the MAC address - will this
> be the MAC address of the printer interface, in which case, will there be
> any problem in the fact that the first leg of the journey is actually
going
> to the MAC address of the switch into which the computer is plugged?
>
> Also, if the switch doesn't really know where to send the packets, will
> they also get sent to the router, and hence to the ADSL link? Is this a
> potential security problem, or is it not something I need to worry about
> because noone is going to be looking for these packets?
>
> (I gather that a hub just connects the ethernet segments without doing
> anything to the data, but the devices that are on the market now all seem
> to indicate that they are switches, so I understand that these look at the
> packets)
>
> Sorry if these questions are couched in the wrong terms, but it just seems
> unlikely to me that an ethernet switch that does not know about the
> particular protocol in use would be able to send the data to the right
> place.
>
> Or am I just worrying unecessarily, (a little knowledge being a dangerous
> thing) and it will all just work?
>
> Tim Lyons.

In article <s%91c.8091$(E-Mail Removed)>, "Benedict
Addis" <(E-Mail Removed)> wrote:

>It'll work fine. Switches work on the ethernet layer in the world of MAC
>addresses, and are blissfully unaware of IP. They do inspect the
>information - called frames not packets at this layer - but routing
>decisions are only made on IP data. If the frame doesn't contain IP, the
>data stays on the LAN side of the router, with the MAC address used to
>decide which port the data goes to.
>
>Cheers, Benedict from ITchest.
>--

Benedict,

Thanks very much for the very helpful reply both on this and on how they do
the equipment at the price, that was very detailed and considered.


One thing I didn't quite understand is whether IP is considered. You seem
to be saying the switch is unaware of IP, but then you say routing
decisions are made on the basis of IP? When is IP considered and when not.

(anyway, it looks as though I shouldn't have anything to worry about).

Thanks,
Tim

On Wed, 03 Mar 2004 21:37:16 +0000, (E-Mail Removed) (Tim
Lyons) wrote:

>One thing I didn't quite understand is whether IP is considered. You seem
>to be saying the switch is unaware of IP, but then you say routing
>decisions are made on the basis of IP? When is IP considered and when not.
>
>(anyway, it looks as though I shouldn't have anything to worry about).

IP addresses are considered when it is acting as a router, so when
data is be transferred between the Internet side to the local network
it is routing and looking at the IP level.

When data is just being switched between devices on the local network
IP addresses are not considered. This means that you can use
Appletalk, IPX etc on the local network and data will be switched
between devices successfully.

Basically there are two completely separate bits of hardware in the
box, one that just acts as a switch and the other that acts as a
router. The router part watches for traffic on the switch that is
intended for it and injects traffic into the switch when it receives
it from the Internet.
--
Andy Norman (E-Mail Removed)
http://www.norman.cx/
Replace the fish with my first name to reply

Andrew Norman wrote:


> Basically there are two completely separate bits of hardware in the
> box, one that just acts as a switch and the other that acts as a
> router. The router part watches for traffic on the switch that is
> intended for it and injects traffic into the switch when it receives
> it from the Internet.

You may find it eaiser to visulise if you imagine a fifth port on the
switch - that is inside the box and is connected to the ethernet port on
the router.


--
Cheers,

John.

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