Re: [tlug] Class B Hubs not suitable for data center use?

[Jonathan Q <jq@example.com>]

On Thu, Aug 29, 2002 at 10:17:20AM -0400, Josh Glover wrote:

>A switch, however, is doing some simplistic routing. IIRC, a switch
>maintains an ARP cache to send a packet addressed to a certain IP
>address to the port where the ethernet interface having the hardware
>address corresponding to that IP address is connected.

Works for me.  The switch is doing switching (layer 2) though,
not routing (layer 3), unless of course it is a layer 3
switch.  What,  you may ask then, is the difference between
a layer 3 switch  and a router?  Not very much.  A layer 3
switch is basically a router with a whole bunch of ethernet
ports and probably no serial ports.  It is quite possible to
use a powerful layer 3 switch as a network core router, as
long as the network isn't too big.  If you need a Cisco 12000,
that probably isn't going to work :-)

The description of the use of/need for buffer memory is spot-on.
The switch has to process packets, and if it doing a lot of
complex switching (trunking, etc.) and is also under heavy load, 
the packets might sometimes be coming in faster than the switch can
switch them.  As long as the switch has more switching fabric 
bandwidth than the sum of its ports, this is not likely to happen,
but if the switch does not, then it could really need that buffer
memory sometimes.  Also, if a packet is fragmented, the switch
may store it there.

Going further, switches that use store-and-forward switching
will need somewhere to keep the packet while the whole thing is
arriving.  Guess where one good place might be? :-)

To keep this slightly more on topic, have any TLUGgers ever
used anything from the Linux Router Project?

Jonathan
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