All language subtitles for 011 RFC1918 - Class A, B, C and IPv4 Link Local Addresses.en

So once again, orif see 1918 discusses IP addresses that are not roadable on the Internet.

They are three blocks of addresses, one class A network, 16 Class B networks and 256 Class C networks.

Here are the range of addresses once again.

And remember, when you are sending traffic internally from an IP address such as 10.1, that one,

that one to a website such as Google dot com or Facebook dot com, your IP address has to be nattered

or network address translated to a public IP address such as 15 dot one, but one that one.

This is a public class address and this is a private class address.

These addresses will not be accepted by Internet service providers and therefore will not be routed

onto the Internet unless, of course, an Internet service provider forgot to add an access list blocking

traffic from these networks.

So in this example, my PC has an IP address of 10 dot zero zero six.

That is a private IP address, which is not a roadable on the Internet, but I am able to ping Yahoo!

Dot com, which has a public IP address of 87 dot 248, dot 122, 122.

And that's because my IP address is being nattered or network address translated by my router when I

send traffic to the Internet.

Here's another example.

Ping Google dot com.

The pings succeed because once again my IP address is being netted.

That is not covered in this video.

Please refer to other videos for explanations of network address translation, but in brief that will

translate one of these IP addresses to a publicly roadable address when traversing a router.

That's how I'm able to use a private IP address on my local PC but still be able to access devices on

the Internet.

My address is being nattered when I traverse my local Internet gateway, which could be as simple as

your router at home, which connects you to the Internet.

The next special IP address range is the IP version four link local addresses or more formally, dynamic

configuration of IP version four link local addresses as per orif C 397.

Microsoft referred to this address order configuration method as automatic private IP address or HIPPA.

So that's Microsoft IP Version four link local addresses.

Now this is used where a PC is configured for DHP or dynamic host configuration protocol, but no DHP

servers are available, so an IP address cannot be allocated via DHP and therefore the PC automatically

chooses an IP address in the range 169000 248 020.

This allows computers to use a link a local IP addresses for communication on a local segment.

Now in the really, really old days of networking going back to Windows three point one.

If you wanted to PCs to communicate, you had to either allocate an address using DHP or you had to

manually configure the IP addresses on the PCs to communicate with each other these days.

That's not necessary because IP Version four link local addresses will allow two computers to communicate

with each other when no DHP server is available.

So if you connected to PCs back to back using a cable, they'd be able to communicate with each other.

Without the user having to configure static IP addresses on those devices.

The PCs would simply use an IP address in this range and be able to communicate with each other.

Hosts randomly generate the host specific portion of the address.

This is a Class B address.

Notice the mosque to find 5.0 5.0 zero, which indicates that the first octets is a network and hosts

will randomly choose the host specific portion of the address.

Once again, this makes the lives of non-technical users a lot easier because they can simply connect

two devices together without the need of a DHP server allocating addresses, the two pieces can immediately

communicate with one another.

The user doesn't have to configure a DGP server or manually configure IP addresses on the PC's.

As long as the two pieces are connected via a cable or a local segment through a switch.

As an example, they can communicate using IP.

So a PC with IP address 169000 to Five-fold.

At one point one can communicate with another PC, which for example, chose an IP address of one six

nine to five for one to two.

No manual configuration is required.

In this example, I'm using consecutive addresses, but typically the addresses chosen by the hosts

are random and won't be sequential like in this example.

Be careful, however, with this address range, it's non roadable.

In other words, the hosts can communicate on the local link, but the traffic is noncredible.

This can cause issues because users will be able to communicate with other devices on the local segment

or local link.

But they will not be able to communicate with the devices on the Internet or devices in a different

subnet.

So if you type IP config on a PC, for example, and you see that the PC has an address in the range

169 or 204 DOT extracts, that means the PC was not able to get an IP address via DHP and dynamically

allocated itself an IP version for link local address.

No DHP server was available and thus an IP address wasn't allocated to the device.

It simply chose an address from the 169 204 address range.