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[music]

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Okay, so let's start out
with the early Internet.

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What did that look like?

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So what we're talking about here

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is the 1960s - the early 1960s.

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I would like to say - and yes, I
can actually say that was before

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I was born, good - but
the early Internet,

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some terms you may
have heard of before,

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DARPA or ARPA.

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DARPA stood for The Defense

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Advanced Research
Projects Agency.

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And the early Internet started

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out as a project from -

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I'm not sure if I'm 
pronouncing it correctly,

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if people say DARPA or D ARPA,

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never actually really
looked that up -

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but it started out as a research

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project from them
and they created

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something called the ARPANET.

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And originally, way back in the day,

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the ARPANET was very simple.

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It simply consisted of two
hosts which were mainframes,

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so this is even
before laptops or

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PCs were generated. You had

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these two monstrous computers
that were talking to each other,

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and that was the early
form of networking,

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having one mainframe be able to
connect and get the resources of

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another mainframe.

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It was a point-to-point
connection

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using circuit switching lines,

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actually using the phone lines.

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The mainframes were located
at different universities,

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different colleges.

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I think they were in the
same state originally.

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I think they were both in
California originally.

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But they used basically
the telephone

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lines to get to each other

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and transfer their data.

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Wait, went a little fast there.

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So keep in mind, back in
these early days here,

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there was no such thing as a
LAN - as a Local Area Network.

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And this is important
to conceptualize

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because I don't know if
you're like me or not,

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but when I try to
visually think,

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visually picture in my mind,

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data going across a network,

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the image that comes to
my head is, number one,

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I imagine data coming into my laptop -

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so inbound or ingress data -

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and I envision that as a series
of electrical pulses, right?

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Zz, zz, zz, zz, electrical
pulses coming in,

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and these electrical
pulses are being

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interpreted as 1s and 0s.

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So my NIC card is seeing this electricity
bouncing around on the cable,

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and it's interpreting that as
a series of just thousands

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of 1s and 0s coming in
really really quickly.

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And when I think in terms
of sort of the OSI model

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and the stack and all that stuff, the
first thing that comes to my mind is

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okay, those electrical pulses,
that's my physical layer.

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That's Layer 1 of the OSI model -

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the electricity coming
into the NIC card -

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and then I start going
up the OSI model.

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This is the way I
envision. I say, Okay,

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well, the next one is the
data link layer - Layer 2.

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And at the data link layer, my NIC
card says, Okay, let's see here.

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What rules am I following?
What protocol am I following?

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Oh, I'm doing Ethernet.

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So according to the
rules of Ethernet,

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the first few pulses
of electricity

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are the pre-amble and
the Ethernet frame.

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The next few pulses
of electricity

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are the destination MAC followed

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by the source MAC.

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Then eventually, Layer 2 says, I'm done.

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I've looked at a
few hundred bits.

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I've been able to interpret
that as an Ethernet frame.

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Within those few hundred bits, it
told me that the next section is

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going to be IP, and so now we
go up to the networking layer.

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When I visualize this,
I start at Layer 1,

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I go to Layer 2, and
then Layer 3 and on up.

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Why I'm bringing it up right
here is because originally,

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when the original
ARPANET was designed,

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there really wasn't a Layer 2.

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There was a Layer 1.

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It was a circuit
switched line using

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telephone lines
for one mainframe

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to call another
mainframe, but there

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was no such thing as Ethernet

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originally, back in these days,
back in the early 1960s.

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So there was no such
thing as MAC addresses.

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A lot of times, people
assume that historically,

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Layer 2 came out first,

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MAC addresses, and then
IP came out after that.

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But it's actually
just the opposite.

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TCP/IP came out before local
area networks came out,

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before Ethernet.

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So as it says here,
All communications

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originally were point-to-point,

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and initially, it was
like circuit switching,

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which is another way of
saying, the phone lines.

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And then, as more and more
networks start coming up,

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they were still point-to-point -

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one device talking
to another device -

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but they start using other types
of media at the physical layer,

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like satellite uplinks, like
direct cable connections.

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I don't mean cable modem,
I mean a physical,

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hardwired cable from one
mainframe in one building

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to another mainframe
in another building.

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That's what I'm
talking about there.

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So as these point-to- point
networks were being developed,

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as it says, There was a need to
develop a protocol so that hosts

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on these disperate
networks could

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communicate with each other.

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So the idea was, Okay, I've just

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developed a very
primitive network

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where my mainframe can
talk to another mainframe.

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Now, what if I expand that to
where my mainframe now has the

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ability to talk to six
other mainframes?

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Still direct connections.

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What if I expand that
a little bit further?

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What if I say, I
want my mainframe

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to talk to Sally's mainframe,

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and then jump through
Sally's mainframe

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to Bob's mainframe on the

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other side? Now, it's
not point-to-point,

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it's me talking
to somebody else,

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and then going through them to

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somebody else.

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And they start saying, Okay, we

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need some sort of
address to do that.

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So when I connect
to Sally, I need

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to have some way of telling her,

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Hey, I don't really
want to talk to you.

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I don't really need your data.

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I just need you to take what I'm

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sending you and
pass it on to Bob

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behind you. So this is where the
whole idea of TCP/IP originally

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became invented.

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They said okay,
well, we need some

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sort of address so that when I'm

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sending my data to Sally,
she knows it's not for her,

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it's for the person
behind her, so

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she can establish a connection.

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We also need to figure
out some ways to make,

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that data reliable,

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like how do I know if I send
something to Bob way out there,

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how do I know if it got there?

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How long should I wait
before I determine that oh,

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it doesn't look like it got there.

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What should I do about that?

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So they actually developed TCP
right along the same time as IP.

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So TCP was developed to answer

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questions of how do I make
this very unreliable,

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very primitive connection
reliable for me?

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What do I do when stuff is lost?

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Then of course, they put IP along

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with that so we can
have addressing.

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Just to give you
some interesting

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terminology, back in the original ARPANET,

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these two or three colleges or

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universities that had mainframes

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talking to each other,

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that they actually developed
a whole unique box,

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a whole unique system that the

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mainframe would
connect to and then

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these boxes - these
black boxes - is

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actually what form the network.

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These black boxes would use the

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circuit switching
lines to talk to

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each other. And
they were called--

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has anybody studied the history of

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the Internet? Does
anybody know what

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those original - I
would say routers -

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what was the name
of the very first

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routers that were developed that

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these mainframes connected
to talk to each other?

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Does anybody know?

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It actually has kind of a
funny sounding acronym.

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They were called IMPs or
Internet Messaging Processors.

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They were huge.
They were like the

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size of a refrigerator, and of course,

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the mainframe was like the
size of your whole house.

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But the mainframe would connect

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to this big
refrigerator size box

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called an IMP and it actually was the
IMP that needed to be addressed.

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The IMP needed to
have an address

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so it could talk to the IMP in Standford,

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could talk to the
IMP in Berkeley,

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or the IMP in Stanford

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could talk to the
IMP in Los Angeles.

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That's where they
originally came up

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with the idea of
Layer 3 addressing.

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The main point I
want you to take

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away from here is
that number one,

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the very, very first
networks were

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point-to-point only,
because number two,

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there was no concept of
local area networks.

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There was no concept
of something

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called a broadcast domain where

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a whole bunch of devices could
see each other on the same wire.

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That had not been created yet.

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This is what networks looked
like back in the early days.

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You had these internet messaging
processors connecting to always uo

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permanent circuits.

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The original Layer
3 protocol that

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they used to address
these things

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actually wasn't even IP.

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They came up with a precursor to that,

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which was called the Network

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Control Protocol - NCP.

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And NCP didn't even really-- the
only kind of addressing it used

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was like for port numbers,

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like whatever protocols were
running on that mainframe,

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each protocol had sort of
its own unique port number

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and that's how they
addressed things.

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And then of course, we
had dial-up circuits,

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where people would use modems
to connect to each other,

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or satellite networks.

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So these were the early days.

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Then people said - and this
is what I described earlier -

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they say, Well, what
if I, in the future,

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need to jump through something?

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What if I need to connect--

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as we can see here, this mainframe

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on the far left wants to connect
all the way to the mainframe in

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the bottom, so we've got to jump

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through a couple
things to do that.

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So it was the vision of these
early Internet pioneers

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that if somehow
people could connect

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these disparate
networks together

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- a satellite network connected

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to a modem network
connected to a

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dial network - if
they could somehow

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connect all these
things together,

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you would now have networks
connected by a series of hops.

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And so there was going
to be a need for

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some kind of networking
addressing scheme,

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flow control, air
correction and detection,

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and all that stuff, and that
is where TCP/IP was born,

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with a need to
solve the problems

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introduced by what you see right here.

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So the original designers
of TCP/IP said,

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Okay, well one of
the things we're

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going to need is each hop in

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the network is going to need an address

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so when we send data, that

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hop knows is that data for you,
or for someone behind you?

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And so the original
designers of IP said,

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Okay, well let's see here.

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Everything is
viewed by computers

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as binary. It's just 1s and 0s, 1s and 0s,

252
00:10:53,561 --> 00:10:54,892
it's just a string of binary.

253
00:10:54,892 --> 00:10:56,900
So they said, Well,

254
00:10:56,900 --> 00:10:59,647
in however many
meetings they had,

255
00:10:59,647 --> 00:11:00,609
they decided and that address is

256
00:11:00,609 --> 00:11:02,796
going to be 32-bits long.

257
00:11:02,796 --> 00:11:04,960
They said that a unique network

258
00:11:04,960 --> 00:11:07,071
address is going to
be 32-bits long,

259
00:11:07,071 --> 00:11:08,753
and they said, Okay,
well, you know--

260
00:11:08,753 --> 00:11:12,040
remember this is like
the late 1960s now,

261
00:11:12,040 --> 00:11:16,399
like 1969, 1970 - and
at this point in time,

262
00:11:16,399 --> 00:11:20,372
there's literally a handful
of these networks.

263
00:11:20,372 --> 00:11:22,413
So they said, Well,
let's see here.

264
00:11:22,413 --> 00:11:24,060
A 32-bit address,

265
00:11:24,060 --> 00:11:26,126
I don't really see
how there's ever

266
00:11:26,126 --> 00:11:27,474
going to need to be anymore than

267
00:11:27,474 --> 00:11:29,158
a couple of hundred networks.

268
00:11:29,158 --> 00:11:30,807
This is all experimental.

269
00:11:30,807 --> 00:11:32,509
We're just seeing if this works.

270
00:11:32,509 --> 00:11:34,040
So of this 32-bit address,

271
00:11:34,040 --> 00:11:37,413
we'll just say that
the first 25% of it -

272
00:11:37,413 --> 00:11:41,319
the first 8-bits - will
represent the network,

273
00:11:41,319 --> 00:11:42,842
and then the remaining bits will

274
00:11:42,842 --> 00:11:46,477
represent that unique
IMP or mainframe

275
00:11:46,477 --> 00:11:48,247
on the network.

276
00:11:48,247 --> 00:11:50,597
Keep in mind, the
original IP address

277
00:11:50,597 --> 00:11:52,229
was 32-bits long - just like

278
00:11:52,229 --> 00:11:55,536
it is today - but key difference was,

279
00:11:55,536 --> 00:11:57,240
it was understood that of that

280
00:11:57,240 --> 00:12:00,759
32-bit address, only
the first eight

281
00:12:00,759 --> 00:12:03,337
bits at the front
end represented

282
00:12:03,337 --> 00:12:04,639
the network address.

283
00:12:04,639 --> 00:12:07,403
If you think in terms of binary,
you realize that with eight bits

284
00:12:07,403 --> 00:12:09,314
to play with, you're
pretty limited

285
00:12:09,314 --> 00:12:10,871
in how many networks you have.

286
00:12:10,871 --> 00:12:14,432
As a matter of fact, you only
have 254 networks available.

287
00:12:14,432 --> 00:12:15,960
Now with eight
bits, technically,

288
00:12:15,960 --> 00:12:17,648
if you think of every possible

289
00:12:17,648 --> 00:12:19,384
combination of
binary you can come

290
00:12:19,384 --> 00:12:23,220
up with from 00000 up to 11111,

291
00:12:23,220 --> 00:12:26,050
and everything in
between, technically,

292
00:12:26,050 --> 00:12:29,516
that gives you 256 combinations

293
00:12:29,516 --> 00:12:33,974
of numbers, of bits you can come up
with with eight bits to play with.

294
00:12:33,974 --> 00:12:36,263
But the early
designers of IP said,

295
00:12:36,263 --> 00:12:41,712
Well, two of those combinations are
not going to be usable as an address.

296
00:12:41,712 --> 00:12:45,239
The combination where
the network is all 0s,

297
00:12:45,239 --> 00:12:47,651
so the first eight bits,
if those are all 0s,

298
00:12:47,651 --> 00:12:49,915
that represents like
a default route -

299
00:12:49,915 --> 00:12:51,538
a route to anywhere.

300
00:12:51,538 --> 00:12:56,222
Then the other combination is
if all of those bits are 1s,

301
00:12:56,222 --> 00:12:57,865
that's considered a broadcast.

302
00:12:57,865 --> 00:13:00,202
It's like sending
something to anybody.

303
00:13:00,202 --> 00:13:04,179
So those two numbers out
of 256 you could not use,

304
00:13:04,179 --> 00:13:06,718
that left 254.

305
00:13:06,718 --> 00:13:10,557
Back in 1969, 1970, they were thinking,

306
00:13:10,557 --> 00:13:11,444
We're never going to use

307
00:13:11,444 --> 00:13:14,462
254 networks. This
is experimental.

308
00:13:14,462 --> 00:13:15,687
This is for fun.

309
00:13:15,687 --> 00:13:19,122
Of course we know, that didn't
turn out to be the case.

310
00:13:19,122 --> 00:13:23,314
Now what's kind of interesting
is, it was actually very forward

311
00:13:23,314 --> 00:13:25,162
thinking of these people to come

312
00:13:25,162 --> 00:13:27,369
up with a networking
address where

313
00:13:27,369 --> 00:13:30,206
you had a network address and
then a bunch of host bits.

314
00:13:30,206 --> 00:13:34,469
Because if you think about it,
there were no LANs back then.

315
00:13:34,469 --> 00:13:35,864
There were no broadcast domains.

316
00:13:35,864 --> 00:13:37,721
It was just point-to-point.

317
00:13:37,721 --> 00:13:39,520
They could've come up with
a scheme where they said,

318
00:13:39,520 --> 00:13:42,359
Okay, every device is just
going to have a 32-bit number.

319
00:13:42,359 --> 00:13:44,812
We're not going to divide this
between network and host.

320
00:13:44,812 --> 00:13:46,784
You're going to
have a unique name.

321
00:13:46,784 --> 00:13:48,128
I'm going to have a unique name.

322
00:13:48,128 --> 00:13:51,716
We're all just going to know
each other's unique names.

323
00:13:51,716 --> 00:13:52,826
But they didn't do that.

324
00:13:52,826 --> 00:13:55,340
They took those 32-bit
number and they divided it -

325
00:13:55,340 --> 00:13:59,592
8 bits for the network, 24
bits on the end for host.

326
00:13:59,592 --> 00:14:02,224
Because they did
that, it was setting

327
00:14:02,224 --> 00:14:04,269
the stage for a few years later

328
00:14:04,269 --> 00:14:07,353
when LANs and Ethernet
would come out

329
00:14:07,353 --> 00:14:08,770
and those host bits would take

330
00:14:08,770 --> 00:14:10,687
on a lot more relevance.

331
00:14:13,683 --> 00:14:16,839
So we can see here in
this particular case,

332
00:14:16,839 --> 00:14:19,217
we've got four unique networks.

333
00:14:19,217 --> 00:14:22,027
So if we only have
8-bits to play with,

334
00:14:22,027 --> 00:14:24,246
it would say something like,
Okay network number 1,

335
00:14:24,246 --> 00:14:27,491
you can see there, it's going
to be 7 zeros followed by a 1.

336
00:14:27,491 --> 00:14:32,015
Network number 2, it's going to
be 6 zeros followed by a 10.

337
00:14:32,015 --> 00:14:34,264
So as long as those
8-bit patterns

338
00:14:34,264 --> 00:14:35,903
are unique from each other,

339
00:14:35,903 --> 00:14:37,223
they're different,

340
00:14:37,223 --> 00:14:40,615
they could be recognized as
being different networks.

341
00:14:46,198 --> 00:14:50,653
All right, now here
we go into the 1970s.

342
00:14:50,653 --> 00:14:55,440
So in the late
1970s, now Ethernet

343
00:14:55,440 --> 00:14:57,254
and Token Ring
came on the scene.

344
00:14:57,254 --> 00:14:58,793
Some of you guys might
be saying, Token Ring?

345
00:14:58,793 --> 00:15:00,781
What's that? That's not part
of the CCNE. You're right.

346
00:15:00,781 --> 00:15:03,411
Token Ring died out
many, many years ago,

347
00:15:03,411 --> 00:15:04,764
but back in this day,

348
00:15:04,764 --> 00:15:09,215
they were competing Layer 2
protocols, data link layer protocols.

349
00:15:09,215 --> 00:15:11,640
Both Ethernet and
Token Ring were

350
00:15:11,640 --> 00:15:14,125
founded on the
same idea that you

351
00:15:14,125 --> 00:15:16,748
could have a bunch of devices,

352
00:15:16,748 --> 00:15:19,345
still probably mainframes
or big servers,

353
00:15:19,345 --> 00:15:21,873
but a bunch of devices
all connected

354
00:15:21,873 --> 00:15:25,115
to some common network media

355
00:15:25,115 --> 00:15:28,380
and able to see each other, be
able to talk to each other.

356
00:15:28,380 --> 00:15:29,533
For example Ethernet,

357
00:15:29,533 --> 00:15:34,254
the original Ethernet was a big
thick coaxial cable, very similar

358
00:15:34,254 --> 00:15:36,294
to the cable that goes
into your cable TV set.

359
00:15:36,294 --> 00:15:39,116
It was big, it was yellow,
it wasn't really bendable,

360
00:15:39,116 --> 00:15:40,722
and the idea was you could have

361
00:15:40,722 --> 00:15:43,581
several mainframes
all clamped into

362
00:15:43,581 --> 00:15:46,573
that same cable and if they
were running Ethernet,

363
00:15:46,573 --> 00:15:49,327
now they could see each
other on that cable.

364
00:15:49,327 --> 00:15:52,006
If any mainframe started
transmitting voltage,

365
00:15:52,006 --> 00:15:53,852
started transmitting
electricity on that cable,

366
00:15:53,852 --> 00:15:58,548
you had more than one device on
that cable that could see it.

367
00:15:58,548 --> 00:16:01,734
This is the whole idea
of a broadcast domain.

368
00:16:01,734 --> 00:16:04,628
A broadcast domain
is a collection

369
00:16:04,628 --> 00:16:07,492
of devices connecting
to a common

370
00:16:07,492 --> 00:16:11,182
network media, let's just say
it's a cable to make it simple.

371
00:16:11,182 --> 00:16:14,276
In that broadcast domain, if one

372
00:16:14,276 --> 00:16:16,162
of those devices
starts using that

373
00:16:16,162 --> 00:16:18,905
network media, starts
transmitting electricity on it,

374
00:16:18,905 --> 00:16:22,617
voltage on it, all the
other devices see that.

375
00:16:22,617 --> 00:16:24,204
They're privy to that.

376
00:16:24,204 --> 00:16:25,412
So that was different, right?

377
00:16:25,412 --> 00:16:27,094
Back in the early
internet, it was

378
00:16:27,094 --> 00:16:28,703
just two devices connected to

379
00:16:28,703 --> 00:16:30,956
a cable and that was it.

380
00:16:30,956 --> 00:16:32,959
Now, with Ethernet,
you've got the

381
00:16:32,959 --> 00:16:35,673
concept of three or four or five

382
00:16:35,673 --> 00:16:37,449
devices could all
be connected to

383
00:16:37,449 --> 00:16:38,604
that same cable and they could

384
00:16:38,604 --> 00:16:41,191
all see each other.

385
00:16:41,191 --> 00:16:43,482
So now we have
another-- now we had

386
00:16:43,482 --> 00:16:45,549
a requirement that 
did not exist previously.

387
00:16:45,549 --> 00:16:49,894
Previously with just two
devices on a cable,

388
00:16:49,894 --> 00:16:53,529
when device A started
fluctuating the electricity,

389
00:16:53,529 --> 00:16:55,496
there's only one
place it could go -

390
00:16:55,496 --> 00:16:59,336
device B. Device B knew, Okay, if
I see some electricity coming in,

391
00:16:59,336 --> 00:17:02,418
some 1s and 0s, it's
got to be for me

392
00:17:02,418 --> 00:17:04,955
because there is
only me and device A

393
00:17:04,955 --> 00:17:05,527
on the cable.

394
00:17:05,527 --> 00:17:07,188
There's  nobody else it could be for.

395
00:17:07,188 --> 00:17:11,035
There was really no need for any
kind of addressing at Layer 2

396
00:17:11,035 --> 00:17:13,225
because it was point-to-point.

397
00:17:13,225 --> 00:17:15,859
Now with the broadcast
domain, with Ethernet,

398
00:17:15,859 --> 00:17:18,159
we do have the requirement
for an address,

399
00:17:18,159 --> 00:17:22,650
because now we could potentially
have 30 devices all seeing that

400
00:17:22,650 --> 00:17:25,191
same electrical
energy, all being

401
00:17:25,191 --> 00:17:26,700
privy to these 1s and 0s going

402
00:17:26,700 --> 00:17:28,941
across the cable, and
now they need to know,

403
00:17:28,941 --> 00:17:30,219
Is that for me

404
00:17:30,219 --> 00:17:32,254
or can I safely ignore it?

405
00:17:32,254 --> 00:17:34,051
So that's why with
Ethernet they said,

406
00:17:34,051 --> 00:17:38,112
Okay, we need to build in an
address called a MAC address,

407
00:17:38,112 --> 00:17:41,755
a Layer 2 address into Ethernet, so
that when I put stuff on the wire,

408
00:17:41,755 --> 00:17:44,246
I can address it to a
unique individual.

409
00:17:44,246 --> 00:17:46,542
And so when I see stuff
coming on the wire,

410
00:17:46,542 --> 00:17:50,783
I know if it's for me
or if it's not for me.

411
00:17:50,783 --> 00:17:52,728
Now also keep in mind that the

412
00:17:52,728 --> 00:17:54,821
original developers
of Ethernet and

413
00:17:54,821 --> 00:17:59,026
Token Ring, they said, Well,
Ethernet and Token Ring,

414
00:17:59,026 --> 00:18:01,711
there's protocols out there

415
00:18:01,711 --> 00:18:03,142
right now that it could carry,

416
00:18:03,142 --> 00:18:06,299
like Ethernet might be
carrying IP behind it,

417
00:18:06,299 --> 00:18:09,237
but maybe in the
future someone will

418
00:18:09,237 --> 00:18:11,430
develop other types
of protocols.

419
00:18:11,430 --> 00:18:14,048
We don't want to limit-- as
a developer of Ethernet,

420
00:18:14,048 --> 00:18:15,911
let's say I'm the
designer of Ethernet,

421
00:18:15,911 --> 00:18:18,461
I don't want to
limit or restrict

422
00:18:18,461 --> 00:18:22,038
myself to where my
Ethernet protocol

423
00:18:22,038 --> 00:18:26,002
is only ever going to be
able to carry IP packets.

424
00:18:26,002 --> 00:18:29,035
I want to design it so it's
fluid, so it's scalable,

425
00:18:29,035 --> 00:18:32,197
so that if anybody develops
another protocol five,

426
00:18:32,197 --> 00:18:35,439
ten, fifteen years from
now, my Ethernet protocol,

427
00:18:35,439 --> 00:18:40,640
which was developed way back in
1972, can carry that new thing.

428
00:18:40,640 --> 00:18:44,606
So this is why Ethernet needed
its own unique address.

429
00:18:44,606 --> 00:18:46,552
A lot of times when
we think of Ethernet,

430
00:18:46,552 --> 00:18:49,395
logically in our minds we
think, Oh, Ethernet carries IP.

431
00:18:49,395 --> 00:18:50,415
Ethernet carries IP.

432
00:18:50,415 --> 00:18:52,858
Well, that's true,
but Ethernet can

433
00:18:52,858 --> 00:18:55,555
carry hundreds of
different protocols,

434
00:18:55,555 --> 00:19:03,022
not just IP. So the designers
of Ethernet were to assume that

435
00:19:03,022 --> 00:19:05,080
a frame might carry
non-IP protocols

436
00:19:05,080 --> 00:19:07,362
so they put their own address

437
00:19:07,362 --> 00:19:08,995
into an Ethernet frame.

438
00:19:08,995 --> 00:19:13,995
[music]