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 00:00:40,000 and you'll often find this, where certain RFCs are superseded by 10 00:00:40,000 --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.