network segmentation without using vlans

[Kristian Erik Hermansen]

On Feb 19, 2008 4:48 PM, James Knott <james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org> wrote:
> Please read again that part about the link integrity test.  It is
> performed periodically.  If there's no response the line is considered
> disconnected.  Will Linux or any other OS send or receive data on a
> disconnected ethernet port?
>
> I based my post on "Ethernet - The Definitive Guide", by Charles E.
> Spurgeon, published by O'Reilly, on page 132 for the link integrity test
> "10BASE-T transceivers continually monitor the receive data path for
> activity as a means of checking whether the link is working correctly.
> The transceivers also send a link test signal to one another to verify
> the integrity of both twisted-pair links".  Information on
> auto-negotiation starts on page 85.  I have known about both for many
> years.  It's the link integrity test, that allows the NIC connect light
> to turn on.
>
> I am quite familiar with ethernet wiring.  Pairs 1 & 3 (pins 4&5 and
> 1&2) are the minimum required for ethernet to work.  As I mentioned
> above, without that link integrity test succeeding, data will not be sent.
>
> Also, if you just want to monitor you can use a hub or a special device
> called an ethernet tap.  Also, some switches can configure a port as a
> monitor for other ports.  Linux, in the 2.4 kernel, provided a way to
> turn off the transmitter, while still receiving.  I don't know if that
> feature is present in 2.6.
>
>
> Incidentally, I'm employed as a senior technician for a company that
> does specialized work for telecommunications companies, such as Bell,
> Telus and Allstream.  A part of my work involves networking, including
> routers, switches, VoIP and PPP links.  My career, in both
> telecommunications & computers, spans almost 36 years and I also studied
> electrical engineering at Ryerson.  I do have some idea of what I'm
> talking about, even without referring to texts.

Maybe I should buy you a beer next time I come into town :-)  I also
have background education in Electrical Engineering, in addition to a
degree in Computer Science, but not nearly as much industry
experience.  Sounds like you could be my Dad!  Maybe the wise old sage
could slap some sense into me at a future conference encounter...heh
-- 
Kristian Erik Hermansen
--
"It has been just so in all my inventions. The first step is an
intuition--and comes with a burst, then difficulties arise. This thing
gives out and then that--'Bugs'--as such little faults and
difficulties are called--show themselves and months of anxious
watching, study and labor are requisite before commercial success--or
failure--is certainly reached" -- Thomas Edison in a letter to
Theodore Puskas on November 18, 1878
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