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and you'll often find this, where certain RFCs are superseded by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