just a quick review,
he said. Keep in mind that even though when we look at our classical addresses and we say Okay
for class A address for the sub net mask 255.0 point 0.0 Our system reads on a binary
so 255.0 point 0.0 is the first octet entirely set to one,
and the remainder is set to zero.
For that reason, you have eight bit set to one.
Sometimes this address is referenced as slash eight.
That slashing number is going to tell you how many bits are set to one of the sub net masks.
So when we go to Class B that has 255.255 point 0.0.
The first two octaves, or 16 bits, is set to one.
That's where you get your slash 16
classy address. You have the 1st 24 bits at 21
so that's where you get your slash 24.
If you keep that in mind, we have a couple more things to talk about, like default address ranges before we can expand upon that and talk about classical ranges
as I mentioned earlier. Subject mask. It's worthless without an I P address
and an I P address is worthless without a sub net mask.
We always want that sub net mask.
Any time I say what's a subject mask?
You should be able to go to a system, do an IP config and see the mask that's being used.
However, if you are unable to find a sub net mask for particular address, there's some assumptions you can make.
Now remember, an assumption isn't a cold, hard fact that wins out in every case.
If you're given a sub net mask that will always trump this default.
But if you're not giving a subnet mask, look at the first auction of the I. P address.
At that first octet falls in the range of 1 to 1 26.
Then you consider it to be a class a address with slash eight sub Net mask or 255.0
It's the first octet falls in the range of 1 28 to 1 91 assumes Class B.
If you notice. When I turned, 27 was skipped,
127 is reserved for a troubleshooting and testing tool called the Loop Back.
So it's not a mistake.
It really is. 1 to 126 for a and 120 to 191 for B.
If the first ox it falls in the range of 1 90 to 2 to 23
that's a classy with a 24 bit mask.
There are also Class D and D sub net masks.
Class D is used for multicasting,
where I send a message out to multiple systems.
Sometimes this is done through videoconferencing or imaging computers.
You'll see less about multicasting in this class.
No, you're ranges of I P addresses. Be able to look at an I p address and say, That's class B. That's classy.
But be flexible enough to know that if you're given a different mask,
that's always going to be the one you go with.
The question becomes, Why is all of this so important?
Why do we really care about the network ID versus the host ID and so on?
What we have to do is be able to determine whether or not traffic is local or remote.
So let's say I'm on a sub net and I'm an on client host whose I P address is 10.1 point 1.1.
If you go back to a chart, you'll know that if the first octet falls in the value of 1 to 126 that's Class A.
So we'll use class A sub net mask here.
I've got some other hosts on the network that all have a Class A sub net mask, and they're all in the 10 Network.
If I want to ping 10.1 point 1.10
and you look at the second illustration, you'll see that what happens is my system will evaluate the addressing. I'm trying to reach and determine if it's all my network or remote network
by looking at I P addresses of my destination and the sub net mask. My client system says that that's on the same network as me.
So it moves immediately to sending out an Air P broadcast which says, Hey, whose I P addresses this.
The computer, 10.1 point 1.10, comes back and says, That's me and here's my Mac address.
So if the traffic is determined to be local, and the client system sends out an therapy broadcast.
But what about if the traffic is remote
going back to the scenario where I'm at a computer? 10.1 point 1.1 with a Class A mask? I paying 172.16 point 1.1?
That's not a local address, so an era P broadcast isn't going to help me.
What do I need to do? In that case,
I need to send that traffic to a router.
Another word for a router is a default gateway.
Your default gateway is where you send traffic that's not in your local network.
You need that router to redirect the traffic to the right network.
In this case, because of the fact the traffic is not local goes to my default gateway,
which you can see in the middle of my screen. I've used the I P Command.
At the very least, it's going to show you my address, my sub net mask and who My default Gateway is
the client, because it looks at the I. P address based on the mask, says this isn't local
and then knows to send the traffic to the router.
Assuming the router is properly configured, the router is able to pass the traffic onto the destination.
So it's important to understand those ideas because if you're taking the test and you can paying a local host,
you're just trying to connect locally,
then the default gateway doesn't matter, and you never use the default gateway if you're just communicating locally.
If you're trying to communicate remotely, you have to make sure that you have your router properly configured.
Remember, your router should always be on the same network that you're on.
Otherwise, you need a router. You get to your router,
so I think you'll probably see some sort of trouble shooting issues where you can't connect locally. Then you can't connect remotely enough to try and isolate what the problem is.
Also mentioned. Tools
I. P. Conflict is good to see and remember that if you're online X or UNIX,
maybe the remote host are trying to get as far away enough through a series of routers.
Don't forget the tools Trace route with UNIX and tracer it with windows.
Those are the tools that will show you it goes throughout our A B or C. So those are handy tools we can use
just wrapping up this section.
We've talked about I p addresses and the fact that an I P address is divided into a network ID and a host.
The way you know that is your sub net mask.
We've looked at default classical add dressing like Class A, B and C addresses.
So anything whose first octet has fallen between one and 126 we can assume his class to a
anything between 128 and 191 is Class B,
and 190 to 2 to 23 is classy.
And of course, remember the sub net masks
255.255 point 255.0.
A lot to remember from this section,
and we also talked about why that significance That way we can tell if traffic is local. Remote
traffic is local was sent on an era P broadcast
traffic is remote. That traffic goes to our local router and perhaps out through the Internet.
This is really critical for the exam.
But even beyond that for your life as a network technician,
I'm going to really encourage you to go back and watch this again. If this is new to you,
make sure you're really solid on those key principles because we're going to take this piece and build on it in the next section.