[wellylug] Dummy ethernet crossover?

[Ewen McNeill]

In message <20040928060120.16229 at mail.pbp.net>, "Edmund A. Hintz" writes:
>    This makes good sense... In talking with a few folks in meatspace
>here I was thinking the same thing. My next step will probably be to try
>turning off the auto-negotiation stuff and see if it works. Will have to
>wait for morning though, I left the hack cable back at the office...

Random other thoughts which may help:
- the transit/receive pairs are polarised, so you want to be sure you've
  connected the right ones together (but even then I don't expect it to
  work without more, due to the "catch 22" nature of which end sends
  first...)

- if you are doing what I think you're doing, then really you don't need
  a physical carrier, you just need the driver to _think_ there is carrier
  (since I believe unlike the snort situation, you don't actually need to
  receive any data across that port).  In which case a software solution
  may be more appropriate (again if you're doing what I think you're
  doing, you don't have all the source -- but there may be enough source
  amongst the bits that have been open sourced to allow you to short
  circuit the "test for link is up and report" into a "report link is
  up in the driver).

Finally since someone mentioned it, the Ethernet "carrier" isn't simply a 
a DC offset, the more important thing is akin to a "keep alive" pulse
that lets the interface know that there is a live connection at the
other end (and 10baseT, 100baseT, etc, all have their own patterns of
pulses, etc -- auto negotiation is effectively selecting amongst these).

The PDF link I posted earlier has some EE (electrical engineering)
details of how it works.

Ewen