So these are the private IP addresses, 10 is a class A, example, 172.16 to 172.31 is a class B and
the 192.168 range is a class C.
Now, don't forget, there are public IP addresses in those ranges.
So 1 to 9 and 11 to 126 are public class addresses.
These are examples of Class B public addresses, 128 to 172.15 and then 172.32 to 191.255.255.255
and then class C is 192 to 192.167 and 192.169 to 223.255.
So based on RFC 1918, some Class B and some Class C addresses were allocated for private addresses.
Now, public addresses used to be managed by the INTERNIC, but they have been succeeded by the IANA
or Internet assigned numbers authority.
The IANA manages the remaining supply of IP addresses to try and ensure that IP address depletion is
pushed out as long as possible.
But these days, you may struggle to get IP version for public addresses as parts of the world have
already run out.
So who's in charge of IP addresses in different parts of the world?
Here are some examples.
So the IANA allocates public IP addresses to one of these groups as an example, RIPE are incharge of
IP addresses in Europe.
For the CCNA course, you need to know three types of NAT,
the first one is Static Nat,
Second one is Dynamic NAT
and third one is PAT.
Now, static NAT maps, a private IP version 4 address to a public IP version 4 address, this
is a one to one mapping.
This is very useful when a device must be accessible from outside the network.
For example, you have a Web server in your internal network that needs to be accessible from devices
on the Internet.
So this type of NAT is often used for servers that require a static IP address, Dynamic NAT maps,
a private IP version 4 address to a public IP version 4 address from a group of public IP version
4 address or from a pool of addresses.
This could be used as an example where two companies merge and they're using the same IP address space.
So you have two companies, for example, using IP addresses, 10.1.1.0 and the devices in those
two companies need to talk to each other rather than renumbering your addresses.
You can use Dynamic NAT to allow those devices to talk to each other.
It's not very efficient and should only be used when absolutely necessary.
Now port address translation or PAT maps, multiple private IP addresses to a single public IP address.
So in other words, you're taking many IP addresses and mapping them to a single public IP address.
Think of your network at home.
You may have multiple PCs, iPhones, iPads or other devices that all need to access the Internet.
ISPs, however, will typically only give you one IP address for your home network, so you may have
three or four or maybe even more devices, let's say 10 IP devices that are using one public IP address.
So 10 devices or or as many devices as you've got at home are using private IP addresses.
And those addresses are then NATTED to the public IP address on your router.
This uses port numbers to differentiate between the different translations,
hence the term port address
translation, PAT is also known as NAT overloading.
We are overloading a single IP address with multiple IP addresses.
It's a type of dynamic NAT and is the most common type of NAT in use today and you'll typically find
it all over the place in businesses as well as your home network.