So what if I want all of the benefits of layer two and the benefits of layer
three?
Well, for the most part, traditionally speaking, we'd say, well, tough luck.
You're going to have to choose one or the other.
But modern networking gives us an option that might actually achieve this.
And this is known as an access layer fabric.
The idea here is that we're going to adopt that fabric concept we talked about
earlier,
especially within the context of the data center, but now we're applying it to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
especially within the context of the data center, but now we're applying it to
our campuses.
So the concept of a fabric is saying that I've got some devices here.
And I have an underlay network.
And remember, we say that the underlay is what I have.
And so I configure maybe EIGRP routing here.
This is all layer three.
Life is good there.
Like now, I'm going to create an overlay network, usually via tunnel mechanisms WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Like now, I'm going to create an overlay network, usually via tunnel mechanisms
.
And this is going to give me the network that I want.
Furthermore, the fact that I can use VXLAN to get me layer two, even over layer
three underlays,
means that I could actually build out a layer two network, whoops, layer two,
that allows
me to have devices on all of these switches that are on the same subnet, not
one over on
the left, not two on the right.
And so this is going to be kind of interesting because we're actually getting WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so this is going to be kind of interesting because we're actually getting
layer three underlay,
layer three physical connections, and yet we're getting the benefits of layer
two.
So when we consider the pros and cons of this solution, the idea here is that
we have
layer three scaling, which is absolutely wonderful.
We don't have to worry about spanning tree protocol anymore.
That's a huge benefit of layer three.
And yet, despite having this as sort of a layer three access layer type of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And yet, despite having this as sort of a layer three access layer type of
deployment,
we get layer two flexibility.
So I don't need to worry if in the future, or for that matter, if today I need
devices
to be able to communicate it layer two, even if they're in different network
closets.
Now there are still downsides to this.
First and foremost, we are going to need layer three switches, and specifically
layer three
switches that are capable of running the XLAN. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
switches that are capable of running the XLAN.
And so these are probably still going to be a little bit pricey, priceier than
just standard
layer two switches.
And furthermore, this does introduce complexity.
Because we're going to need to understand fabrics, underlays, overlays, VX
lands.
It's going to be a little require expertise that today our team might not have.
But there is an upside to this, which is that oftentimes we'll deploy a network
controller
to do a lot of this for us. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
to do a lot of this for us.
This leads us to a conversation where Cisco has created a pre-packaged solution
that
gives us all of this. And this is known as software defined access, oftentimes
abbreviated
as SDA. SDA access is going to use a controller that is going to allow us to
just deploy switches,
plug them into other switches, and our configurations just get automatically WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
plug them into other switches, and our configurations just get automatically
updated from this controller.
The controller is known as catalyst center, and it's going to be responsible
for managing
this network for us, and it does a lot of it without us having to intervene.
Now there's still complexity in setting up the controller and setting up the
environment,
but it does reduce the overall complexity.
So how does this directly map to access layers and distribution layers?
Well it changes the nature of our mapping a little bit. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Well it changes the nature of our mapping a little bit.
We are going to put the distribution switches here in the middle.
And again, these are going to be extending layer three out to our edge.
So if I have an access closet over here with a stack, access closet over here
with a switch
stack, and maybe even a pair of switch decks by the way, and then access closet
up here
with a switch deck.
What I'm going to do is I'm going to build a layer three network out to each
one of these. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
one of these.
And so here, this is my layer three underlay.
So far, this looks just like a layer three access model.
But the difference is now I'm going to deploy VXLAN over the top, and this is
going to give
me my overlay.
So what this functionally looks like is VXLAN tunnels are going to be built
among all of
these other switches.
We're going to get a full mesh of the XLAN tunnels. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We're going to get a full mesh of the XLAN tunnels.
And I believe I've got them all.
Yeah, I think so.
So all of these switches have the XLAN tunnels between them, which creates that
giant cloud,
where we can say maybe we'll just wrap it all up in there.
So we can say, you know what, we don't care about what happens inside of this
cloud.
Instead, all I know is that my host here and my host up here that are
connecting in at
different access closets can all be part of the same VLAN, and they can all be WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
different access closets can all be part of the same VLAN, and they can all be
part of
the same subnet.
So this is why we come back to this idea that we get pretty much all the
benefits of layer
two and layer three.
And then we just have to compare it to the downsides of managing a fabric and
consider
those and decide if that's maybe where we want to go with our access layer
design.
Now we're going to be talking a lot more about Cisco's software defined access
later on
in the course, and we're going to have an even better sense at that point of
all of the
pros and cons of deploying such a solution. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
pros and cons of deploying such a solution.