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and you'll often find this, where certain RFCs are superseded by 10

other newer RFCs and therefore become obsolete 11

Essentially a lot of the information that we're studying 12

in networking, comes originally from RFCs or Request For Comments. 13

They are important to understand and read if you want to get 14

into the nitty gritty or details of specific protocols 15

However, in networking one of the jokes you may hear is that 16

If you can't sleep at night, go and read a bunch of RFCs 17

and that's going to put you to sleep. 18

However some RFCs are actually done in good humor, and there's 19

even an RFC, RFC 1149 describing IP over AVIAN Carriers 20

or in other words, how to transmit IP packets using pigeons 21

and I am not joking, go and have a look at RFC 1149 22

and you can see how it's possible to send data using pigeons. 23

Obviously done in good humor. 24

Now being serious for a moment, one of the famous RFCs 25

that you need to know is RFC 1918. 26

RFC 1918, discusses Private IP Addresses 27

which are non-routable addresses on the internet these addresses 28

will be blocked by Internet Service Providers or ISPs 29

and can thus not be used for sending traffic unto the internet. 30

So here's RFC 1918, just do a simple search in Google or your 31

favorite search engine and you'll be able to find this RFC 32

or go to tools.ietf.org/html/rfc1918 33

As you can see here, various parties were involved 34

in the drafting of this RFC, and it also obsoletes previous RFCs. 35

This RFC is Address Allocation for Private Internets 36

and explains best practices for the Internet Community 37

with regards to Private Addressing, notice the date February 1996. 38

That's a long time ago, even that many years ago 39

it was recognized, that there was a problem 40

with the exhaustion of IPv4 addresses 41

As I'm recording this in 2015, 42

the Address Registrar for the Americans has recently run out of 43

IP addresses, so this RFC was created to try and increase 44

longevity of IPv4 and it's actually worked quite well. 45

The exhaustion of IPv4 has been postponed, 46

for longer than a lot of people expected. 47

In this RFC they mention some of the problems of the internet 48

which are still challenges today, for example how the internet has 49

has grown beyond anyone's expectations and this RFC describes the 50

use of private IP addresses internally within organizations 51

and those IP addresses would be NAT'd or Address Translated 52

when traffic is sent unto the internet. 53

Notice in the RFC, it states that the Internet Assigned 54

Numbers Authority or IANA, has reserved the following blocks 55

of IP address space for private internets. 56

So we have network 10, which is a class A address 57

networks 172.16 up to 172.31 which are class B networks and 58

192.168 all the way up to 192.168.255 which are class C networks. 59

They refer to CIDR in the RFC and we'll discuss CIDR in a moment 60

and I'll explain what this mask mean, but essentially notice that 61

a single class A network, 16 contiguous class B networks 62

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