Re: Network monitor

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At the risk of going wildly off-topic for this list,
here's a quick tutorial on what a hub and switch are.

In the early days of Ethernet, the data was carried on
thick yellow cables (thickwire). There was a definite upper
length to the cable - as there are electrical considerations 
to the signals.

Then came along thinwire, using thin coax cable and standard
T-pieces to tap signals off. Still having length limits.B

Boxes called repeaters were developed, which connected 
Ethernet segments together. They electrically repeat the signal,
so you can have a longer run and more machines on a network.

Next come learning bridges. 10Mbps Ethernet can easily be saturated
if traffic is busy - ie. many stations talking to each other,
or if one (more) stations are broadcasting wildly - broadcast storm.
A learning bridge applies some intelligence. It is a computer with
two interfaces. It registers (learns) the MAC addresses on each interface
and only permits traffic across when the destination MAC is on the other

So we end up with the classic 'backbone' and spur network.
All the backbone really is is an Ethernet segment separated from the
rest of the (say) departmental segments via bridges.

(Can;t remember the company which first made an Ethernet switch -
I even worked with one once)
Switches now come along - in te era now of twisted pair.
They are a learning bridge on each port.
So each port is its own collision domain, offering data transfer 
between any pair of ports at a theoretical top speed.

So to summarise a Hub is a multi-port repeater.

A Switch is a multi-port bridge.

And SNMP-managed switches can be asked to give lots of parameters -
including the MAC addresses of all stations attached to any port.

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