1
00:00:00,000 --> 00:00:05,000
Now RFCs or Request For Comments are formal documents

2
00:00:05,000 --> 00:00:10,000
from the IETF or Internet Engineering Task Force

3
00:00:10,000 --> 00:00:14,000
which are typically drafted via a committee from multiple vendors

4
00:00:14,000 --> 00:00:17,000
and are reviewed by interested parties.

5
00:00:17,000 --> 00:00:21,000
RFCs are intended to become Internet Standards and the final

6
00:00:21,000 --> 00:00:25,000
version of an RFC will become an Internet Standard and there

7
00:00:25,000 --> 00:00:30,000
often no changes are permitted to that RFC.

8
00:00:30,000 --> 00:00:35,000
However changes or updates can be made in subsequent RFCs

9
00:00:35,000 --> 00:00:40,000
and you'll often find this, where certain RFCs are superseded by

10
00:00:40,000 --> 00:00:44,000
other newer RFCs and therefore become obsolete

11
00:00:44,000 --> 00:00:48,000
Essentially a lot of the information that we're studying

12
00:00:48,000 --> 00:00:53,000
in networking, comes originally from RFCs or Request For Comments.

13
00:00:53,000 --> 00:00:57,000
They are important to understand and read if you want to get

14
00:00:57,000 --> 00:01:02,000
into the nitty gritty or details of specific protocols

15
00:01:02,000 --> 00:01:06,000
However, in networking one of the jokes you may hear is that

16
00:01:06,000 --> 00:01:11,000
If you can't sleep at night, go and read a bunch of RFCs

17
00:01:11,000 --> 00:01:14,000
and that's going to put you to sleep.

18
00:01:14,000 --> 00:01:18,000
However some RFCs are actually done in good humor, and there's

19
00:01:18,000 --> 00:01:26,000
even an RFC, RFC 1149 describing IP over AVIAN Carriers

20
00:01:26,000 --> 00:01:30,000
or in other words, how to transmit IP packets using pigeons

21
00:01:30,000 --> 00:01:35,000
and I am not joking, go and have a look at RFC 1149

22
00:01:35,000 --> 00:01:37,000
and you can see how it's possible to send data using pigeons.

23
00:01:37,000 --> 00:01:42,000
Obviously done in good humor.

24
00:01:42,000 --> 00:01:47,000
Now being serious for a moment, one of the famous RFCs

25
00:01:47,000 --> 00:01:50,000
that you need to know is RFC 1918.

26
00:01:50,000 --> 00:01:54,000
RFC 1918, discusses Private IP Addresses

27
00:01:54,000 --> 00:01:58,000
which are non-routable addresses on the internet these addresses

28
00:01:58,000 --> 00:02:02,000
will be blocked by Internet Service Providers or ISPs

29
00:02:02,000 --> 00:02:06,000
and can thus not be used for sending traffic unto the internet.

30
00:02:06,000 --> 00:02:12,000
So here's RFC 1918, just do a simple search in Google or your

31
00:02:12,000 --> 00:02:16,000
favorite search engine and you'll be able to find this RFC

32
00:02:16,000 --> 00:02:24,000
or go to tools.ietf.org/html/rfc1918

33
00:02:24,000 --> 00:02:28,000
As you can see here, various parties were involved

34
00:02:28,000 --> 00:02:33,000
in the drafting of this RFC, and it also obsoletes previous RFCs.

35
00:02:33,000 --> 00:02:37,000
This RFC is Address Allocation for Private Internets

36
00:02:37,000 --> 00:02:42,000
and explains best practices for the Internet Community

37
00:02:42,000 --> 00:02:48,000
with regards to Private Addressing, notice the date February 1996.

38
00:02:48,000 --> 00:02:51,000
That's a long time ago, even that many years ago

39
00:02:51,000 --> 00:02:55,000
it was recognized, that there was a problem

40
00:02:55,000 --> 00:02:59,000
with the exhaustion of IPv4 addresses

41
00:02:59,000 --> 00:03:01,000
As I'm recording this in 2015,

42
00:03:01,000 --> 00:03:06,000
the Address Registrar for the Americans has recently run out of

43
00:03:06,000 --> 00:03:12,000
IP addresses, so this RFC was created to try and increase

44
00:03:12,000 --> 00:03:18,000
longevity of IPv4 and it's actually worked quite well.

45
00:03:18,000 --> 00:03:22,000
The exhaustion of IPv4 has been postponed,

46
00:03:22,000 --> 00:03:26,000
for longer than a lot of people expected.

47
00:03:26,000 --> 00:03:30,000
In this RFC they mention some of the problems of the internet

48
00:03:30,000 --> 00:03:34,000
which are still challenges today, for example how the internet has

49
00:03:34,000 --> 00:03:40,000
has grown beyond anyone's expectations and this RFC describes the

50
00:03:40,000 --> 00:03:45,000
use of private IP addresses internally within organizations

51
00:03:45,000 --> 00:03:51,000
and those IP addresses would be NAT'd or Address Translated

52
00:03:51,000 --> 00:03:54,000
when traffic is sent unto the internet.

53
00:03:54,000 --> 00:03:58,000
Notice in the RFC, it states that the Internet Assigned

54
00:03:58,000 --> 00:04:04,000
Numbers Authority or IANA, has reserved the following blocks

55
00:04:04,000 --> 00:04:07,000
of IP address space for private internets.

56
00:04:07,000 --> 00:04:12,000
So we have network 10, which is a class A address

57
00:04:12,000 --> 00:04:20,000
networks 172.16 up to 172.31 which are class B networks and

58
00:04:20,000 --> 00:04:28,000
192.168 all the way up to 192.168.255 which are class C networks.

59
00:04:28,000 --> 00:04:35,000
They refer to CIDR in the RFC and we'll discuss CIDR in a moment

60
00:04:35,000 --> 00:04:41,000
and I'll explain what this mask mean, but essentially notice that

61
00:04:41,000 --> 00:04:46,000
a single class A network, 16 contiguous class B networks

62
00:04:46,000 --> 00:04:51,000
and 256 class C networks have been allocated for private addresses.