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Now RFCs or Request For Comments are formal documents
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from the IETF or Internet Engineering Task Force
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which are typically drafted via a committee from multiple vendors
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and are reviewed by interested parties.
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RFCs are intended to become Internet Standards and the final
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version of an RFC will become an Internet Standard and there
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often no changes are permitted to that RFC.
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However changes or updates can be made in subsequent RFCs
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and you'll often find this, where certain RFCs are superseded by
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other newer RFCs and therefore become obsolete
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Essentially a lot of the information that we're studying
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in networking, comes originally from RFCs or Request For Comments.
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They are important to understand and read if you want to get
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into the nitty gritty or details of specific protocols
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However, in networking one of the jokes you may hear is that
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If you can't sleep at night, go and read a bunch of RFCs
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and that's going to put you to sleep.
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However some RFCs are actually done in good humor, and there's
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even an RFC, RFC 1149 describing IP over AVIAN Carriers
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or in other words, how to transmit IP packets using pigeons
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and I am not joking, go and have a look at RFC 1149
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and you can see how it's possible to send data using pigeons.
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Obviously done in good humor.
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Now being serious for a moment, one of the famous RFCs
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that you need to know is RFC 1918.
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RFC 1918, discusses Private IP Addresses
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which are non-routable addresses on the internet these addresses
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will be blocked by Internet Service Providers or ISPs
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and can thus not be used for sending traffic unto the internet.
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So here's RFC 1918, just do a simple search in Google or your
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favorite search engine and you'll be able to find this RFC
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or go to tools.ietf.org/html/rfc1918
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As you can see here, various parties were involved
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in the drafting of this RFC, and it also obsoletes previous RFCs.
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This RFC is Address Allocation for Private Internets
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and explains best practices for the Internet Community
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with regards to Private Addressing, notice the date February 1996.
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That's a long time ago, even that many years ago
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it was recognized, that there was a problem
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with the exhaustion of IPv4 addresses
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As I'm recording this in 2015,
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the Address Registrar for the Americans has recently run out of
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IP addresses, so this RFC was created to try and increase
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longevity of IPv4 and it's actually worked quite well.
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The exhaustion of IPv4 has been postponed,
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for longer than a lot of people expected.
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In this RFC they mention some of the problems of the internet
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which are still challenges today, for example how the internet has
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has grown beyond anyone's expectations and this RFC describes the
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use of private IP addresses internally within organizations
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and those IP addresses would be NAT'd or Address Translated
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when traffic is sent unto the internet.
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Notice in the RFC, it states that the Internet Assigned
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Numbers Authority or IANA, has reserved the following blocks
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of IP address space for private internets.
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So we have network 10, which is a class A address
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networks 172.16 up to 172.31 which are class B networks and
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192.168 all the way up to 192.168.255 which are class C networks.
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They refer to CIDR in the RFC and we'll discuss CIDR in a moment
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and I'll explain what this mask mean, but essentially notice that
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a single class A network, 16 contiguous class B networks
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and 256 class C networks have been allocated for private addresses.
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