>> When testing, avoid using a switch or a hub (spoken:
>> 'multi-port-repeater').
> How do you figure?  Modern bridges (Ethernet switches in marketing
> speak) operate at full wire speed with impressively little latency
> added.

Actually, a true hub has even less latency than a layer-2 switch.
Switches have to receive at least the first 48 bits of the data (the
Ethernet destination address) before they can tell what port(s) to
forward the packet out, meaning a delay of at least 48 bit times,
probably more because of channel seizure and suchlike goop.  A true
hub, on the other hand, just blindly echoes carrier, introducing only
as much delay as is incurred by demodulating and remodulating - perhaps
on the order of a couple of bit times, and doesn't care about channel
seizure leadins and such - indeed, it could be argued that it's fair to
call it a layer-1 device.

Of course, most (layer-2) switches can be set for store-and-forward
rather than cutting over immediately after the Ethernet destination MAC
address (and early cutover works only when both ports are at the same
speed anyway).  This will increase latency, of course, but if your
network suffers from a lot of collision fragments, jabbers, etc, it can
be worthwhile to do so, and many people do.  There's also latency
introduced if the destination port is busy when the switch would like
to send to it, though this "can't happen" under certain common
conditions (only two hosts involved, running full-duplex at the same
speed, with the switch never sending packets on its own initiative).

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