Need for Crossover Cables



  • I worked for a long time at a med center where all the nics had auto MDIX. Never gave it a thought. My first build of a test machine for pfsense wouldn't work, and I was stumped for several days. Then it occurred to me that the nics I used were fairly old 3Coms and that they didn't have auto MDIX. Without auto MDIX a straight thru cable won't work between two nics, and that is what I was trying to do in building a perimeter firewall. The problem was solved when a WRT54GL was inserted in between the two nics in switch mode (no cable in the Ethernet port). That router has auto MDIX on the switched ports. A crossover cable would also work, but I don't have a single one. In the future I will use TrendNet nics that have auto MDIX. It is amazing how a little thing like that can stop a pfsense project stone cold, and if it doesn't occur to you to consider crossing over cables, you don't know how to get it to work.



  • I have a 50 cent solution…  OK - Maybe $1

    http://www.cctvcamerapros.com/CAT-5-Wiring-Diagram-s/293.htm



  • @glh1309:

    I worked for a long time at a med center where all the nics had auto MDIX. Never gave it a thought. My first build of a test machine for pfsense wouldn't work, and I was stumped for several days. Then it occurred to me that the nics I used were fairly old 3Coms and that they didn't have auto MDIX. Without auto MDIX a straight thru cable won't work between two nics, and that is what I was trying to do in building a perimeter firewall. The problem was solved when a WRT54GL was inserted in between the two nics in switch mode (no cable in the Ethernet port). That router has auto MDIX on the switched ports. A crossover cable would also work, but I don't have a single one. In the future I will use TrendNet nics that have auto MDIX. It is amazing how a little thing like that can stop a pfsense project stone cold, and if it doesn't occur to you to consider crossing over cables, you don't know how to get it to work.

    Auto-MDIX is mandatory with Gig-E NICs.  If you're using 10/100 cards then they may not have that feature.


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