Tag Archives: adapter

Making an Ethernet Loopback Adapder

This post will be short (and sweet). Ethernet Loopback Adapters are little handy pieces of equipment that route the transmitting pins in an Ethernet jack back to the receiving pins in the same jack. This is good for testing link connectivity on an Ethernet card – if the adapter can establish a link with itself the hardware on the adapter is probably OK. In real life, this can save you hassle quickly testing ADSL modems, routers, switches, desktops and laptops without plugging the device into another jack to get the link light to come on.

This how-to will use an existing Ethernet cable which will be converted to a Loopback cable.  There are lots of guides and video online about creating such an adapter using an Ethernet jack and wires, but this requires having an uncrimped  Ethernet jack, some wires, and a crimper. In my case, a trip to the store to buy the components I already have at home on ready Ethernet cables seemed wasteful (most people will have a cable or two, or can buy a short cat 5 cable for under 2 dollars). I strongly recommend using a cable with a broken or missing jack – after all, we only need one Ethernet jack which is properly wired to a cat5 or higher cable.

1. Cut the cat5 cable a few ( 2 or 3 ) inches from the jack.

2. Strip about an inch from the shielding of the cat 5 cable, revealing 8 separately shielded color coded wires inside.

3. Strip about half an inch from the shielding on four wires: green-white, green, orange-white, and orange.

4. Twist the green-white and orange-white stripped ends together, connecting pin 1 to pin 3.

5. Twist the green and orange stripped ends together, connecting pin 2 to pin 6.

If you have some tape, you may want to cover the tips up. Otherwise, make sure the tips don’t touch each other. The end result will look like this:

twisted pairs on an Ethernet loopback adapter

twisted pairs on an Ethernet loopback adapter

You can test your new loopback adapter in any working Ethernet jack by plugging it in!

You can see the Port line is on for a wireless router with the loopback adapter plugged in:

Link light on with loopback adaper plugged in

Link light on with loopback adaper plugged in

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Slackware 13.37 and the ASUS PCE-N13 Wireless Adapter

ASUS PCE-N13

The ASUS PCE-N13 is not especially pretty, but its cheap, fast, and officially supported!

If you are on the market for a wireless adapter for your Linux desktop, the best bang for the buck today seems to be the ASUS PCE-N13. Not only will ~30$ get you a/b/g/n support, 300Mbps transfer rates, 2 antennas and a PCIe bus, but it also says “Linux Support” right on the box, and not in some fine print in an obscure corner. The only card in my local shop to read that, although all of them work just fine. So this is a *moral* choice as well 😉

The card is indeed supported by the rt2860sta module. Unfortunately, with Both Slackware 13.37 and Ubuntu 10.10, the kernel module fails to bind to the card because the various rt2800 and rt2x00 modules conflict with rt2860sta. The module loads, but all attempts to initialize the card result in error messages. To remedy this, simply blacklist the other modules from loading by adding those modules to /etc/modprobe.d/blacklist.conf like this:

# Blacklist rt2800 and rt2x00 modules
# This will allow the rt2860sta module to bind to the ASUS PCE-N13 card:
blacklist rt2800lib
blacklist rt2800pci
blacklist rt2x00lib
blacklist rt2x00pci

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