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- Let's talk about Automatic
Private IP Addressing,

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also know as APIPA.

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This is something that occurs when,

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usually when your computer
cannot get an IP address

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from a DHCP server.

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If you see the address 169.254.X.X,

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any other numbers after that,

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if you see 169.254,

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that means APIPA and
chances are that means

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that your computer's not
getting the correct IP address

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from a DHCP server.

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And APIPA has kicked in.

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This automatic private
IP addressing is built

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into the Windows system,

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and it originally was created

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so that Windows could be
networked together automatically

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without the use of a switch

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or a router or anything like that.

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But nowadays it kind
of just gets in the way

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of clients trying to obtain IP addresses,

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or it manifests itself

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when a client cannot obtain an IP address.

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And so what we're gonna
do is we're gonna show

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an APIPA address in Windows,
and then we'll show how

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to fix the problem using
the IP config command,

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and also show in the registry,
how to disable APIPA.

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So we talked about APIPA

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or automatic private IP addressing,

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and how it can be a problem sometimes

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and could get in the way

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of your computer obtaining
an IP address automatically.

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To be honest with you, I've had texts

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where APIPA has just driven them bonkers.

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But like any technical
problem, it is solvable.

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So first of all, what I
wanna do is I wanna look

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in the command line and see

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whether or not APIPA is actually running.

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Then we'll go into the registry
and show how to turn it off.

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So first we'll go to
the command prompt now.

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And we'll do one of those ipconfig/alls.

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And we'll see that we got lots and lots

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and lots of information.

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Well, we'll start with
the wireless lan adapter.

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And what we're looking for here

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is auto configuration
enabled, that is APIPA,

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and it says, yes, it's running.

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So we know that APIPA
is actually functioning.

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And so if you ever saw 169.254
here as the IP address,

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it's pretty safe to assume
that you could say, all right,

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this computer was trying
to obtain an IP address

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from a DHCP server, but it couldn't do so

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for one of a variety of reasons.

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The DHCP server could be down,

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the computer might not be
accessing the network properly,

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and so on.

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And at that point it gets the 169.254,

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and the APIPA is applied.

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If we look at the other
adapter, the ethernet adapter,

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we'll see here that yes,

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auto configuration is enabled.

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Even though we're not doing DHCP,

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auto configuration
enabled, that's separate.

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So APIPA is actually
still running on this.

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So we know it is actually
running and you may

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in some environments need to turn it off.

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To do that, we'll go to the registry.

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And the best way to get there
is to go to the run prompt,

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and type regedit.

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So we'll do our trusty
Windows and R combo,

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and we'll type regedit
here and press enter.

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And yes, I had already typed it.

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And here's the user account control.

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We'll just say yes for that.

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And that brings up the registry editor.

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So what we wanna do is we wanna locate

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where the APIPA configuration
is, where we can change that.

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And in here, we're gonna go

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to HKEY local machine,

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system,

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current control set,

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services,

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and we'll scroll all the
way down to T C P I P,

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because APIPA is part of
the TCPIP protocol suite.

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And that's here, open that up.

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Then we'll go to parameters,
and then interfaces.

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And finally, we need
to know which interface

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we wanna turn off.

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And you see, these are just associated

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with big hexadecimal numbers.

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These are security identifiers.

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Or they're globally unique identifiers.

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Not important for the A plus,

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but big hexadecimal numbers associated

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with each of our network adapters.

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And if we look at these, we
can find out which one we want.

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This is the guy I want.

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The second one.

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I know that because of the IP address.

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This is my ethernet network
adapter, 10.254.254.204.

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And it has the default
gateway, 10.254.254.1.

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All the networking
information in here is placed

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in here as values.

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And you can make modifications from here.

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This is really going into
depth with the system.

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Now, you gotta be careful
with the registry.

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If you're ever gonna make any
changes or add information,

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you should back up or
export the entire registry,

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or at least export the key or sub key

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that you're messing with.

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And to do that, you just go
to file and go to export.

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And then you select exactly
what you want to back up.

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A lot of times,

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I'll just back up the
entire registry database.

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This way you're safe.

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If a mistake happens,
you could always go back.

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So always have that backup or that export.

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But what we're gonna
do here is we're going

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to create a new value, a new DWORD.

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So we'll right-click,
select new, and then DWORD.

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And this is gonna be called
IP auto configuration enabled.

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And that's all one word.

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Make sure we spelled that right.

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Ipautoconfigurationenabled, press enter.

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That creates the entry.

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And now we have to assign a value.

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If we press enter for this,

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we'll see the actual DWORD configuration.

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Right now it's set to zero
and that's what we want.

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We really can just set it to zero for off,

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and one for on.

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If we set it to zero, then IP
auto configuration enabled,

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or APIPA will be turned off.

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So that's a little bit about APIPA,

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And now you know what it
is, why it might happen,

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and how you can see whether
it's running in Windows,

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and also how to turn it off if necessary.

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So that's about it for this sublesson.