- [Instructor] Let's talk about loopback plugs.
There are loopback testing devices
for just about any type of communications connection.
It could be a serial connection, an older DE-9 connection.
You may hear these referred to as loopbacks or bounce backs
or null connections.
Whatever you wanna call 'em.
I usually just refer to it as a loopback,
and the most common one
is the ethernet RJ45 loopback connector.
This guy has two ports and the first is the male port,
which has the RJ45 plug,
and then the other side has the female port.
So you can connect this in a variety of ways.
And what we do with this,
the reason we use this,
is really to find one of two things.
One, we can find if a particular cable
is connected to a switch.
So, let's say there's a jack on the wall
and you don't know if it's connected to a switch or not.
You could plug this into the jack
and then that port will light up on the switch.
So you can check it that way.
You could also test a patch cable.
If the patch cable's connected directly to a switch,
you could do that from this end.
And so, to show this, we'll connect this
to a basic four port switch here.
And I'll make a connection to one of the ports now.
And the lights are pretty dim,
but you can see here, there's a power light.
And right now it doesn't have a connection
but it usually takes about 20 seconds or so to show up.
And there it goes.
There's our power connection.
We have a link light for that particular port.
If I was to switch the port,
again it'll take about 20 seconds to register that guy.
And you can do this
with just about any regular switching device.
And that link light should come up
once it registers that guy.
So there you go.
And it shows the port that it is actually connected to.
We see here, it's connected to port five,
and let's see that here.
You have one through one through five here,
and then it'll show that link light.
Regardless of what switch you use, this will work.
But if you have one of those SOHO routers, four port device
that is a multifunction network device,
it may not function properly 'cause effectively
what this guy is is a crossover connection.
Pins one to three and two to six are crossed.
So it's kinda like a crossover cable.
It's not a crossover cable,
but it's like it does the same type of thing.
But instead of the crossover cable connecting like devices
this bounces the signal back
because those wires are crossed inside
the single individual plug.
It's not like they're crossed across a cable.
So, that's the loopback plug.
So again, this may or may not work for your SOHO router.
How often are you actually gonna need that?
This is more for if you have a rack mount 24 port switch,
48 port switch, or that type of thing.
Now, sometimes these fail.
If you have an issue with one of these,
you can use a basic patch tester to test it.
And just plug in the guy and then run your test.
And you should see one and three lit up
because pin one is crossed to three on that plug,
and two and six should light up
because pin two is crossed to six.
That's the essence of a crossover connection.
And then they cross the others for good measure.
Four to seven and five to eight.
And that's good because you can actually use this
for more than just ethernet.
You can use this for other types of networking connections
as well that use those other pairs of pins.
And so it cycles through and there you have it.
That's your loopback adapter.
So it's a nice little device to find out
if the cable's connected to a switch and if so,
what port it is connected to.
Now, there's the better way to do that is to use
a tone generator.
If you have a ton of cables
and you're not sure where the cable is,
and if you plug this in and you don't get a link light,
then you're gonna wanna use a tone and probe kit,
or use your cable certifier that has tone built in
to check for that guy.
Now, that was the first way.
The second thing you can do with this is test the computer.
You can test the network card
to see if it's actually functioning.
And now we'll show that now.
Okay, so here we have the back of the AV Editor
computer we built.
Here is our RJ45 port.
So we can test that.
Let's say that we're not sure that it's working properly
and we either don't have a network connection,
a wired network connection,
or the wired network connection is not giving us
a link light.
We can narrow down the problem by plugging in
the loopback adapter and see if it generates
that link light for us.
Now again, when you plug it in,
it takes about 20 seconds usually to register.
And so we have our loopback adapter here.
And by the way, you don't have to just connect with this.
You can use a patch cable if you want,
and connect that to that side.
And you can do that when you're connecting to the PC
or to a switch, and then you'd use the other end
of the patch cable to connect into the port.
Whatever that port may be.
But we could just connect the RJ45 loopback into the port.
And so we'll do that now.
And we'll give it about 20 seconds and it should light up.
And so 20 seconds passed, and it was just about 20 seconds,
and we got that link light.
So, we know that the network card is working physically.
We know we're getting electricity to the card.
The card is working properly,
and it's bouncing signal back and forth from the card,
from the network adapter into this RJ45 loopback.
And I keep saying card, but this is really integrated
into the motherboard, but the network adapter.
So whatever it is, a network adapter or a switch port,
that'll link up and give you a link light after 20 seconds
or so if it's a working port, if the connection is good.
So, that's a nice little tool to use
to test the physical connection, physical connectivity
and check those LEDs.
Make sure that you have that connectivity.
You know, then we could say, okay,
we were connecting a network cable,
but we weren't getting a link on the PC.
We've ruled out that it's the PC's network adapter.
So now we can go further and test that network connection.
And you might use this, or you might use
your tone and probe kit,
or you might use your cable certifier.
You know, it all depends on how far you have to go with it.
And you know, what the scope of the problem is.
So a little bit about the RJ45 loopback.
You can use that to find particular cables
and what ports they're connected to on a switch,
and identify if the RJ45 connection on the computer
is working properly.
So that's it for this sub lesson.