Re: [SLUG] ethernet couplers

From: rfoxwor1@tampabay.rr.com
Date: Sun Jun 15 2008 - 21:13:47 EDT


---- Chris Mathey <slug@mathey.org> wrote:
 
> CSMA/CD is just for half-duplex communication, which is basically dead.
> I haven't seen a hub in a really long time. If I did find one in my
> environment it would be ripped out immediately :)
>
> Full Duplex Ethernet, collisions are impossible since tx and rx are on
> different wires, and each segment is connected directly to a switch.
> Therefore, CSMA/CD is not used on Full Duplex Ethernet networks.

Yes, if you are not using a hub then you need to use a switch (unless
you have access to a tap device from such as NetOptics). If you are
in need of monitoring your net traffic for whatever reason, you can
do this, if you have a prof. grade switch that can be set up with a span
port. If you are using some of the cheaper switches sold as a
consumer grade item, that choice is not available. For my way of
thinking I could not imagine having a network with no way of checking
the traffic flow. If you (anyone, pl.) think this is not necessary, you just
haven't yet run into the problem that _makes_ it necessary. To do this,
you either use a good* configurable switch, a tap or a hub. Or, guesswork.

* good == $

Sounds like your environment is a good (see *) commercial setup with
proper hardware. But I'd be interested in knowing why you feel a hub
is an inherently bad device to even have installed. Unless someone has
uncontrolled access to your wiring closet, and can just go
around jacking a "sniffer" onto your network without you knowing it.

Or, knowing why someone else felt it necessaary to have installed it
to begin with (such information can be very helpful - sometimes better to
let it lie and quietly watch it to see who was interested in it). It's quite
obvious the hub would not have been installed by you, is it? When you
"rip it out immediately" however, you lose all that people diagnostic. And
remember, physical (e.g. console) access is king. When that happens,
game over.

And it can hardly be about faster internet, when your gigabit LAN
is throttled down to 300k when it hits the first interface downtown
sharing traffic with a thousand kids downloading movies..

Yes I have two hubs at home. One on either side of my firewall.
This is so I can run an instance of wireshark on a third machine,
(eth with no assigned IP) plugged into a hub port, and see what
kind of threats are trying to get in. Or, help debug my wife's
telecommuting when it is acting balky. Using a switch, that would let
me do this, is for me vast economic overkill.

But I am my own purchasing manager. YMMV. Be thankful you
don't have to do that. Right now, "home" IS my "environment".

- Bob

PS in this day and age I would recommend the tap option
for this purpose, see www.netoptics.com e.g. 96443 copper port
aggregator.

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