So why do we need net or network address translation.
The major reason is IP version 4 address exhaustion.
For years there's been a worry that IP version for addresses would run out and the heavy essentially
run out today is the drive to move to IP version 6 because of IP version 4 address exhaustion.
However it's probably more than likely that he's still using an IP version for dress and in a lot of
networks today engineers still need to make the move to IP version 6.
One of the reasons for that is because of RAFC 1918 RAFC 1918 was drafted in February 1996.
So in other words it's been around for a long time.
This discusses the address allocation for private internets.
I'm not going to bore you going through the entire document.
But notice in section 3 they talk about private address space.
The Internet assigned numbers of 30 or I honor has reserved the following three blocks of IP address
space for private internets 10.00 that zero up to 10 or 255 255 255.
In other words a 10 slash 8 Prefect's 172 to a 16.00 up to 1 7 2 3 1 2 5 5 2 5 5.
This is a 1 7 2 door 16 slash 12 Prefect's and then we have 1 1 2 1 6 8 0 2 0 2 1 2 1 6 8 255 255.
This is a 1 9 2 1 6 8 slash 16 Prefect's in my example here.
I'm using a 1 9 2 1 6 8 189 address internally.
What are you using on your PC.
More than likely if you're at home using one of these are provision for addresses in companies as mentioned
such as Apple or HP you may be using a public IP address.
So RAFC 19:18 was drafted to try and conserve IP addresses.
The idea here is that rather than allocating public IP addresses to every device in the Internet devices
within companies could be allocated these addresses and they could be enacted or translated when they
needed to access the Internet with port address translation or pat.
The idea is is that you overloading an IP address hence the term that Cisco uses.
We could have one public IP address used by 500 internal devices.
These are F.C. 19:18 addresses are non ratable on the Internet.
In other words Internet service providers will block or drop in traffic going to or coming from these
address ranges.
Well that's assuming that they've configured they rightest correctly but they should have access lists
blocking those addresses so that they non-radical on the Internet.
These are iffy 19:18 addresses are used internally within organizations and hence we have the term private
addresses used within private networks and public addresses used on the global public internet now.
Technically there's nothing stopping private IP addresses from being routed across the Internet.
The reason they non-radical is because ISP are blocking traffic to or from those address ranges.
So the issue is if private IP addresses are non-profitable how do we get onto the Internet.
Well that's way network address translation that comes in that allows us to translate a private IP address
to a public IP address your Internet service provider or ISP will allocate you an IP address or a range
of IP addresses a router or other type of device will translate to your internal private IP addresses
to that globally readable public IP address.
Now the terminology that Cisco use can be confusing and it's something that people often struggle with
Cecka use the terms inside a local address inside a global address outside local address and outside
global address.
Now the terms used to network address translation can be very confusing.
This is probably one of the hardest things to understand with Nat.
So you use these terms inside a local address inside global address outside local address and outside
global address to try and help you remember these terms.
Think of the following analogy.
The PC in this apology PC one is an insider in your organization.
Insiders in your organization are people who work for your company or who have access to the Insight
Network or local area network.
So this PC is an inside host or inside the server on the other hand is an outsider.
It doesn't belong to your organization.
It's on the global Internet.
It is an outside host the network that the PC is connected to is the local area network.
This is a local LAN or local network.
If you run with a shock on this network and captured packets they would be deemed to be local addresses
because they are on the local LAN the Internet.
On the other hand once again is global.
Think of traces in the Internet as global addresses because they are on the global Internet.
So in other words think of addresses as follows.
Inside a local is the IP address of this inside host on the local LAN inside global is the IP address
of the local PC PC one as seen on the global Internet.
If he sniffed traffic on a local LAN you would see the inside a local address of the PC if he sniffed
traffic using Y shack on the internet you would see the inside global address of the PC outside a local
is the IP address of this outside server.
When seen on the local area network outside global is the IP address of this server on the global Internet.
So in summary this is an inside host.
So we have an inside local address an inside global address the inside hosts IP address on the local
area network is an inside local address this inside hosts IP address when seen on the global Internet
is the insight global address inside host on local network inside.
Host on global Internet this outside PCs IP address when seen on the global Internet uses the outside
global address.
But when seen on the local area network is the outside a local address.
I hope that helps you remember the terms.