[Snort-users] Re: Wiring a "read only" cable (Joe Pampel)

Wynn Fenwick wfenwick at ...4126...
Fri Nov 30 19:26:02 EST 2001

Hi Guys,

Correct me if I'm wrong but this works for a hub only and not a switch.
Switches would get confused at the logical link layer, would they not,
since they would see the same frames on the incoming from the host as
were outgoing to the host?

I have also tried building the cable that has a schematic listed at

While electrically the high-pass filter worked as expected, our Cisco
3500xl compensated for the attentuation, which was obviously off a bit
because the R of the cable may not have been accurate enough, or the C
value of the cap was not tolerant enough.

The host was able to transmit despite the presence of the cap on the Tx


Jay Flowers wrote:

No, this is neither a crossover cable, nor are pins 1 and 2 simply cut.

(I can easily see how colorblindness would make it difficult or
to see that the wire colors of the sniffer cable match the normal one,
the crossover one.)

This is a normal ethernet cable, with pins 1 and 2 shorted over to pins
and 6 on one side, normal wiring on the other.

I suspect this was done by cutting a small amount of insulation off of
3 and 6, and soldering in pins 1 and 2, but I'm sure there are other
to make the splice.

This is a pretty cool trick and looks like it will deal with the problem
just cutting the TX wires on 100baseT (which causes the link to go dead
you can't receive). I've not tried it, but it makes some sense to me why

this works, and I'll believe Josh that it does work.

At 08:23 AM 11/30/2001, Flowers, Jay wrote:
>So this is a crossover cable with pins 1 and 2 cut on the crossed side?

>Jay Flowers
>Integic Health Care
>-----Original Message-----
>From: Lists [mailto:lists at ...2694...]
>Sent: Friday, November 30, 2001 6:19 AM
>To: Josh Oshiro
>Cc: snort-users at lists.sourceforge.net
>Subject: Re: [Snort-users] Re: Wiring a "read only" cable (Joe Pampel)
>I use a simple cable on all of my sniffers. I have successfully used
>cable on Windows 2000 Pro and Server boxes when deploying Snort.
>Give it a shot.

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