One interesting note about enterprise
and corporate networks is that they generally
have more features, and bells, and whistles,
and security than a small office home office.
So from a physical equipment perspective,
one of the big differences is going
to be in the switching environment.
So in a small office home office we
may have a simple 8-port switch.
However, in a corporate environment
they're probably going to have racks and racks of switches.
And they're also going to have different ones
based on where they are.
They'll have some in the wiring closets, referred
to as access switches.
And those access switches can then
connect down to bigger switches at or near the data center.
Those are often referred to as distribution switches.
That's also a likely location to get connectivity
between the corporation and other sites, which
could include connectivity out to the internet
or connectivity up to a remote office or branch office.
And in the main distribution area near the data center,
there's going to be a lot of traffic that
flows through that point in the network.
And to help facilitate moving all that data,
the higher end switches use a feature
known as distributed switching.
And if we have a Layer 2 frame that
needs to be switched when the frame comes in,
if the switch has to take a moment and think about that--
OK, that frame came in here.
And it needs to go out this port.
If that decision has to go to a centralized brain
every single time a frame comes in,
that could be a bottleneck if we have
hundreds or thousands of ports.
And that's where distributed switching can help.
With distributed switching the forwarding information
is distributed out closer to the ports, or at least
the module on that larger switch where those ports exist.
Then as a result, when a frame comes in on this port that
needs be sent out that port, because that learning
and forwarding logic is distorted down
at this level, this module doesn't
have to check in with the centralized brain
to ask it, OK, what do I do?
That information about forwarding
is cached and distributed.
So the switch can make that forwarding decision
without having to bother the central unit every single time.
Also, what we'll typically find in corporate environments
is that they'll have some switches that
also incorporate routing functionality in one box.
So the question might come up, well,
what do you call a box with a whole bunch of ports that
can do Layer 2 forwarding, based on Layer 2
information the frames, as well as make Layer 3 routing
decisions.
Is it a Layer 2 switch?
Or is it a Layer 3 router?
And the answer is it's kind of both
if it has both those functionalities.
And I've seen this often referred to
by many different vendors as a multi-layer switch.
So if you see the term or hear the concept multi-layer switch,
it can be referring to either Layer 3 routing of IP packets
or forwarding of Layer 2 frames, all built into the same box,
referred to as a multi-layer switch.
Back in the 80s when I had my first official corporate job
in the world of IT and networking,
we had dedicated leased lines between our location, which
was in Southern California and a branch office
or remote site in northern California.
And the lease line was fairly expensive.
It was a dedicated circuit between us and our other site.
And because it was really expensive,
we had some fairly intelligent gear
on both ends that could do things
like time division multiplexing and other kind of tricks.
And that way we could utilize that dedicated circuit
as much as possible between our two locations.
And a dedicated circuit, a dedicated leased line
is an example of circuit switching, where
we're moving data frames between point A and point
B over a single path every time.
So all the traffic would go over that leased line from point A
to point B. And then back from point B to point A.
Now, we loved the fact that we had connectivity.
But we didn't love the cost.
So in the late 80s and early 90s,
the big rage was a new technology called frame relay.
And effectively what it did was this.
We had a service provider.
I'll put SP for short.
Instead of having a dedicated leased line,
we would go ahead and rent a logical circuit.
So the central site would connect to the cloud.
The remote site would connect to the cloud.
And then inside the service provider cloud
we'd have a logical connection between the two.
But it wasn't a physical dedicated circuit.
And in this cloud the service provider
had a lot of different paths.
So we might have some of our packets go over one path
and other packets go over a different path.
The key is it's all packetized.
So we're not using the same exact path
as that traffic is moved, or forwarded, or switched,
if you will, over that service provider network.
And that concept of individual packets going over
a network and perhaps not all of them
taking the exact same path, is referred to
as packet switching.
And from a customer perspective, we really
don't care if all the packets take the same path
as long as they get to the other side in a timely fashion.
And in the right order it would be helpful as well.
Another useful idea-- and it's up and coming and will be
for a long time to come--
is the concept of software defined networking,
or SDN for short.
Because think about a large network with lots of gear.
If we had to administer each one of these by connecting to them
and then configuring them, whether there are switches,
or routers, or firewalls, or access points,
connecting to each one of those is a pain in the puzuski.
So at software defined networking,
the concept is this.
We're not going to have the humans touch
the actual infrastructure.
Instead, we're going to have humans interact
with applications.
And that application could go both ways.
It could give us information as a human.
And we could also make changes.
But we're doing it through the application.
And those apps are communicating to controllers.
So there's control.
Looks like we have a controller right here
on the network that's connected to our network infrastructure.
Our applications would interoperate
with those controllers.
And the controllers would then interoperate
with the actual infrastructure.
I hope this has been informative for you.
And I'd like to thank you for viewing.