very low cost ethernet hub with monitor port?

Look on ebay for a 4 port hub. That's where I got mine.

I've heard that vendors have been knwon to use the words interchangable and an Ebay sellor is likely to miss-describe the item, so it's kind of a crapshoot. They will be *very* cheap, so yo might have to buy a couple.

The dongle won't work.

find one where the description gives the manufacturer and p/n, then check on the web site for exactly what it is.

to start you off i have a Netgear dual speed hub, type DS116 - 16 ports of

10/100.

this is 2 hubs, 1 @ 10M and 1 @ 100, with a switch linking them, so a 10/100 device can connect.

as long as all device attach at the same speed, it acts like a simple hub at

10 or 100.

and no - i got it for the same reason, so it isnt for sale.

You need to make sure you get a repeater. As others have said, manufacturers sometimes call products "hubs" which are actually switches. Problem is very few chipset vendors still makes repeating silicon - all the volume moved to switching more than 5 years ago. If you just want 10M repeating, take a look at 3C16700A from 3Com - 8 port repeater. Also from them is 3C16755 which is a 5 port 10/100 repeater with a switch to connect the 10M and 100M collision domains. Both are around $60. Clearly you can buy a small switch for less than half this, but that isn't going to help ;-)

Note that I expect most repeaters to be EOL within the next 12 months as none of the current silicon that I am aware of is RoHS compliant, so it can't be shipped to any regions requiring this complaince.

(snip)

If you can remove the terminating resistor on a dongle receive port, it should be possible to connect it to a pair in the middle of a cable, such that the cable can be used to pass traffic. You won't be using the transmit port for snooping, so don't even connect that.

I don't know which dongles, if any, have a terminating resistor that can be removed. On newer ones, it is likely surface mount, and maybe also be on older ones. That makes is a little harder to remove, but it should still be possible.

-- glen

glen herrmannsfeldt wrote in part:

Only if the isolation transformer is 10base2-style high resistance. But what if the isoXfo is low resistance (50ohm)? Why would a terminating resistor exist? Or is there too much inductance?

-- Robert

The line should be terminated somewhere close to 100 ohms.

10baseT is pretty different, the whole transceiver is isolated from the AUI cable, but not from the ethernet cable. Collision detect is based on the DC (more or less) voltage on the cable, so it can't have a transformer there.

For 10baseT and 100baseTX the line should be terminated at 100 ohms for megahertz range frequencies, the low frequency resistance of the transformer might be lower. It might be that newer ones can terminate from inside the transceiver IC, which would make it harder to remove.

-- glen