A more recent trend in networking is to establish the concept of a fabric
rather than a network.
What exactly is this concept of a fabric?
Well, typically when we're talking about a fabric, we are talking about
creating some form
of overlay network, which runs on top of an underlay network.
The mechanism that we're going to use for this is ultimately going to be by
building tunnels. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
building tunnels.
And the way I often describe this is to say that the tunnels are going to form
the network
that we want, whereas the underlay is the network that we have.
Let's give an example of this.
And one of the best places to look when we're talking about fabrics is inside
of the data
center.
The data center is one of these network places.
It showed up on our hierarchical network model as a block that connects into
the core.
Now, a data center is intended to host an organization's applications and an WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Now, a data center is intended to host an organization's applications and an
organization's
data.
So typically, we're going to deploy a bunch of servers into the data center.
We're going to deploy storage arrays into the data center.
And this is also where we're going to see a significant amount of virtual
ization.
We're talking about virtual servers or VMs, which creates virtual networking
needs.
And that'll be a topic of conversation later on in the course. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And that'll be a topic of conversation later on in the course.
But the data center is a very critical network location.
We need a very firm network model or network architecture that's going to allow
us to number
one, establish uptime.
We need to stay online in our data center.
And furthermore, we do need to continue to focus on scale.
The problem is that a lot of our data center applications and a lot of the
technology we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
technology we
deployed into the data center requires layer two networking.
So if we need layer two networking, that's great except layer two is not really
known
for its scaling.
Or is it known for its uptime spanning tree loops and failures can cause
broadcast storms
on our network.
And so this is a little bit of a conflict of interest between what the data
center needs
and what the data center ultimately has. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and what the data center ultimately has.
Now a traditional data center architecture is going to look a lot like a campus
network.
We're going to have a distribution block that connects into an access block.
And this is where all of these servers and storage arrays are going to connect
in.
Except instead of calling the distribution block by the distribution name in
order to distinguish
us from campus networks, we're going to call this an aggregation block. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
us from campus networks, we're going to call this an aggregation block.
The aggregation block basically is a distribution block, but it's going to have
data center specific
features features such as fiber channel over ethernet.
And virtual port channeling.
And these are the types of technologies that enable us to deploy all of the,
again, applications
and data hosting that's required in order to keep our organization online and
functional.
These days, if an organization loses access to its applications or data, the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
These days, if an organization loses access to its applications or data, the
whole organization
might as well be down.
We might as well not even be trying to work because we probably can't take
customer orders
and a lot of us can't do our jobs without the applications that allow us to do
our jobs.
So this traditional data center model is really problematic because, again, it
is going
to, first of all, enable us to have layer two everywhere, which is good, but it
doesn't
particularly scale well. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
particularly scale well.
We have scaling issues thanks to layer two.
And just thanks to the fact that we only can have a pair of switches here in
the aggregation
layer in the same way we can only have a pair of switches in the distribution
layer.
If our access switches expand out greatly, which can happen in very large scale
data centers,
we could have hundreds of access layer switches.
We might very quickly outgrow our aggregation layer.
And then we have to deploy a new aggregation layer. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then we have to deploy a new aggregation layer.
Well, where does that go?
The new aggregation layer and new access layer.
So a GG and a CC are going to have to connect through the network core to get
to the other
aggregation layer.
Well, this is layer three and therefore we've just broken our ability to have
layer two
stretched between the two different access layers.
And so this is why traditional data center architectures have been overhauled.
So what do we do today? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So what do we do today?
So what we're doing in the data center is we're deploying the fabric concept.
And so this is where we're bringing the conversation full circle to come back
to the concept
of the fabric.
The idea here is I'm going to deploy a different physical network connection,
what we call a leaf
spine network, which can have multiple spine switches.
Let's say we have four spine switches and pretty much as many leaf switches as
we want.
Certainly there are scalability limits, but we can have dozens and even WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Certainly there are scalability limits, but we can have dozens and even
hundreds of these
leaf switches.
And we connect all of these devices up to one another, but we only connect
spine switches
to leaf switches and we only connect, well, leaf switches back to spine
switches.
We don't actually connect spine switches to each other or leaf switches to each
other.
And furthermore, all of these connections are layer three.
So this is known as the underlay. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So this is known as the underlay.
It's the physical network that again represents what we have.
What do we have?
We have a layer three network.
Well, what do we want?
But we've said over and over again that we want our data center to allow for
layer two
connectivity everywhere.
Meaning that if I have a host over here, that's dot one on a subnet, then the
host over here
that's dot 100 on the same subnet and the same broadcast domain should have WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that's dot 100 on the same subnet and the same broadcast domain should have
access to
one another layer two.
So that's great and all except that's not what I have.
I have a layer three fabric, which is great from a scaling perspective.
By the way, this is why we're building it.
This is for the sake of getting this scaling, but we don't want to compromise
on the fact
that we wanted layer two everywhere.
And so how do we get this?
Well, this is going to come from, or as well, maybe I should say it's going to
define what
we want, what we want is a layer two network. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we want, what we want is a layer two network.
So what are we going to do?
Well, we're going to build an overlay.
And in the case of a fabric like this, we're going to get our layer to via a
protocol known
as VXLAN.
It's essentially saying we're going to extend our VLAN technology.
So what VXLAN is going to do is it's going to provide layer two tunnels. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So what VXLAN is going to do is it's going to provide layer two tunnels.
And this is going to create the overlay network.
So what happens is we build VXLAN tunnels among all of these different leaf
switches.
And there's lots and lots of these tunnels.
Keep that in mind.
But ultimately what we're doing is we're creating the network that we want.
We're allowing this host on the left to communicate to this host on the right.
And they have layer two communication, even though the network that we have is
layer
three. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
three.
This is pretty cool.
And it's a big part of software defined networking, which is a whole trend in
networking
these days that ultimately provides us with this same concept, the ability to
deploy a
network that we want over a network that we have.
And oftentimes we're going to use a network controller in order to do that.
That's a big part of the SDN world because building all of those tunnels and
being dynamic
with them can be very cumbersome for you and I to try to manage via the CLI. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
with them can be very cumbersome for you and I to try to manage via the CLI.
So an SDN environment might say we're going to have a network controller that
does all
of this for us.
But regardless of whether we're doing it manually or via a controller, either
way this concept
gives us the fabric that network that we want, even though we have a different
network
underneath it.
Now this type of technology doesn't stop with the data center.
Cisco has a whole campus architecture known as software defined access. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Cisco has a whole campus architecture known as software defined access.
And at the heart of which is their SDN controller known as catalyst center.
We are going to be talking about SD access because it's within scope of the
exam and this
course.
And it's going to be built on VXLAN but it's going to be deployed not to the
data center,
but ultimately to the campus environment.
It's called SD access because it's delivering this layer to connectivity to our
access layer
on the campus side. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
on the campus side.
And so understanding that fabrics can apply yes within the data center but also
outside
the data center is going to be a major part of bringing together our network
designs.
But understanding that we have these traditional architectures that allow us to
deploy access
layers, aggregation layers, distribution layers, those are going to be
absolutely fine,
especially for small and medium networks.
But as we start to grow our networks to very, very large enterprises, we might
want to
consider migrating to some form of fabric. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
consider migrating to some form of fabric.
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