Wow — how’s this for suckage? Another volunteer was installing a pair of DSL modems at my church to connect the LAN in the main building to a building about 800+ feet away (i.e., one modem at the main building and another at the end of a dormant twisted pair that was laid out to the remote building several years ago):
One thing that was driving me nuts with the DSL installation was the fact that the head DSL modem would not work when the EH end was plugged directly into the Dell switch with a straight through CAT-5 cable. I got it to work by plugging the cable from the Dell switch into a small hub I brought along then pluging the DSL modem into this hub. I thought it strange that I was getting a connection from the Dell switch to my hub using a straight-thru cable. Usually one uses either a crossover cable or the “stscking” connection on the hub to connect a switch to a downstream hub. Unless, thought I, that the Dell Switch is auto-sensing and reverses the input & output connections to accomodate either a straight-thru or a crossover cable.A trip to the Dell website confirmed that auto-sensing is a “feature” of this switch.
I called Black Box, who made the DSL modems and talked to a tech about this. He said that the modem is auto-sensing, too, so two auto-sensing devices are fighting each other and never figure out which polarity is which. Inserting my “stupid” hub in line, settled the issue in that both the Dell switch and the DSL modem saw a regular hub connection.
The KISS solution is to simply leave a hub in the line.
I’m glad it wasn’t me!