Original subtitles

Now RFCs or Request For Comments are formal documents

from the IETF or Internet Engineering Task Force

which are typically drafted via a committee from multiple vendors

and are reviewed by interested parties.

RFCs are intended to become Internet Standards and the final

version of an RFC will become an Internet Standard and there

often no changes are permitted to that RFC.

However changes or updates can be made in subsequent RFCs

and you'll often find this, where certain RFCs are superseded by

other newer RFCs and therefore become obsolete

Essentially a lot of the information that we're studying

in networking, comes originally from RFCs or Request For Comments.

They are important to understand and read if you want to get

into the nitty gritty or details of specific protocols

However, in networking one of the jokes you may hear is that

If you can't sleep at night, go and read a bunch of RFCs

and that's going to put you to sleep.

However some RFCs are actually done in good humor, and there's

even an RFC, RFC 1149 describing IP over AVIAN Carriers

or in other words, how to transmit IP packets using pigeons

and I am not joking, go and have a look at RFC 1149

and you can see how it's possible to send data using pigeons.

Obviously done in good humor.

Now being serious for a moment, one of the famous RFCs

that you need to know is RFC 1918.

RFC 1918, discusses Private IP Addresses

which are non-routable addresses on the internet these addresses

will be blocked by Internet Service Providers or ISPs

and can thus not be used for sending traffic unto the internet.

So here's RFC 1918, just do a simple search in Google or your

favorite search engine and you'll be able to find this RFC

or go to tools.ietf.org/html/rfc1918

As you can see here, various parties were involved

in the drafting of this RFC, and it also obsoletes previous RFCs.

This RFC is Address Allocation for Private Internets

and explains best practices for the Internet Community

with regards to Private Addressing, notice the date February 1996.

That's a long time ago, even that many years ago

it was recognized, that there was a problem

with the exhaustion of IPv4 addresses

As I'm recording this in 2015,

the Address Registrar for the Americans has recently run out of

IP addresses, so this RFC was created to try and increase

longevity of IPv4 and it's actually worked quite well.

The exhaustion of IPv4 has been postponed,

for longer than a lot of people expected.

In this RFC they mention some of the problems of the internet

which are still challenges today, for example how the internet has

has grown beyond anyone's expectations and this RFC describes the

use of private IP addresses internally within organizations

and those IP addresses would be NAT'd or Address Translated

when traffic is sent unto the internet.

Notice in the RFC, it states that the Internet Assigned

Numbers Authority or IANA, has reserved the following blocks

of IP address space for private internets.

So we have network 10, which is a class A address

networks 172.16 up to 172.31 which are class B networks and

192.168 all the way up to 192.168.255 which are class C networks.

They refer to CIDR in the RFC and we'll discuss CIDR in a moment

and I'll explain what this mask mean, but essentially notice that

a single class A network, 16 contiguous class B networks

and 256 class C networks have been allocated for private addresses.