Airport Extreme and Ethernet - Trial and Error

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Day 2 of our Ethernet project.

At the very least, we've isolated the problem.



The switch is fine.

If I bring it up to the home office, and plug it directly into the Airport Extreme, it lights up like a Christmas tree.

It's the wires in the walls that are causing our problem.

That's upsetting. But it may not be fatal.

Isolating the Problem

We had Cat5e ethernet wires run throughout our house.

In each case, the wires terminate with a finished "female" wall jack on one side - and in the basement storage closet, they terminate with a standard "male" plug.

The Airport Extreme is in the upstairs home office.
Our switch sits in that basement storage closet.

To connect the Airport Extreme to the switch, I ran a patch cable from an Airport Extreme LAN port, to the wall plate.

Behind the wallplate, the ethernet cable runs to the basement, where I connected the "male" end of that cable to the switch.

This SEEMS like a direct connection.

It's Airport Extreme --> patch cable --> wall jack --> Cat5e --> switch. 

But we got absolutely nothing. The LAN port on the Airport Extreme would not light up. The switch will not light up. No activity. No data transfer.

Bad LAN port? Bad patch cable? No. I attached my laptop to that same LAN port, using the same patch cable, and the computer connected with no problem.

So the router and the patch cable are not causing the issue.

Dead switch? No. When I brought the switch up to the home office, and connected it directly to one of the Airport Extreme's LAN ports using the same patch cable, everything worked.

The LAN port lit up - the switch lit up - even the MyQ device that I attached to the switch worked.

So, are the cables in the wall bad? Potentially. They certainly aren't working.

But I have another idea about the culprit.

Cat5/Cat5e/Cat6 wires have a number of twisted pairs inside, arranged by color. Those wires can be arranged in two different ways - called 568A and 568B.

There's no real difference between the two wiring formats. B is used a LOT more often, but they should be interchangeable. As long as both ends of each wire use the same diagram!

I popped open the wall jack in our office, and confirmed that our electrician used format 568A.

The "male" ends in the basement closet were all also 568A.

So, no problem?

Well.... all of our patch cables are Cat6 - and 568B.

Still, that shouldn't be a problem, based on my research. The wrong-colored wires are in the wrong places, but electricity isn't looking at colors.

BUT, given that it's NOT WORKING, this A-vs-B thing a variable I'd like to eliminate.

(You may remember a similar wiring issue when we were installing our ADT Pulse telephony system.)

We're essentially using a 568A wire as an extension cable for a 568B cable.
I don't know WHY that wouldn't work, but that may not be entirely kosher.

I'm guessing (hoping) that the problem stems from the fact that our internal wires are "female-to-male". My hypothesis is that we're essentially creating a crossover-type cable, with B-male on one side (the patch cable connected to the router) and A-male on the other (the end of the internal cable).

I still don't understand why this wouldn't work, but whatever.

It's either my hypothesis is correct, or the wires in the wall are physically damaged

I have 2 ways of testing this hypo.

First - the half-measure. I'll pick up a 568A patch cable (or an adapter) tonight. We'll be 568A all the way from the Airport Extreme to the switch.

If the router can connect to the switch, we'll know that the A/B swap is causing our problem.

Then - full measure. I'll cut off all of the terminations of the ethernet wires in the wall, and re-wire them all as 568B.

Not fun, but I'm not going to deal with this issue because my electrician randomly chose the less-common wiring diagram.

Now, If the 568A cable doesn't work - we're calling the electrician and contractor back, to re-run cables.

And while he's at it, he can install Cat6.

UPDATE - Fry's didn't have ANY patch cables that were 568A. I tried to use a crossover adapter, no luck. The electrician will return on Friday morning. 

2 comments :

  1. My town just installed its own fiber network, and it's been awesome so far. However, rather than just using WiFi, I'm hooking up my laptop to an ethernet cable. Luckily, I haven't had quite the same frustration as you have had in dealing with the seemingly random changes between T-568A and T-568B cabes! I think we're supposed to use Cat 5e cables, too. https://www.protelecominc.com/services.html

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    1. Ultimately, we got the ethernet working. The problem wasn't with the 568A/B switchoff - it was with the style of cable terminators our technician had used - which apparently were not allowing a consistent signal to pass.

      They made the changes, and things are working well now.

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