So this is the format that we're going to use for our quiz questions.
I'm going to display a question like this on the screen and you're going to
have the
opportunity to again pause the video just to make sure that you have time to
answer.
And then we'll roll right into the explanation, which is why you need the pause
button.
So either way, make sure that you're taking the time to answer these questions
as we go.
So first question here.
And I believe we have seven or eight of these.
Now I'm trying to remember either way.
Well, we've got about that range.
So first question, what description best describes the hierarchical network WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So first question, what description best describes the hierarchical network
model?
Take a moment to review these answer choices and give your best answer.
Now the answer that I would give for this is going to be right here, D, the
principles
that provide structure and scale.
But let's go ahead and go through each one of these because I think that we
could probably
convince ourselves that any one of these answers choices is true.
For example, when we say vendor specific, we might be thinking, okay, is this a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
For example, when we say vendor specific, we might be thinking, okay, is this a
Cisco set
of principles or does this apply broadly to everyone?
And it does apply broadly to everyone.
This is not just something that Cisco proposes and pushes out there.
It's something that all network vendors agree on.
And this is how we should build our networks out regardless of whether we're
using Cisco
hardware or not.
Now next, this one might have caught some people.
It's a template for scaling to very large networks.
It absolutely scales very large networks, but not exclusively. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It absolutely scales very large networks, but not exclusively.
It also scales for very small networks, meaning that I can collapse my layers.
Remember, we could have a collapsed core and distribution layer.
In fact, we could have a collapsed core distribution and access layer.
If indeed we have users coming into the same block and then we connect out to
other blocks,
those are the functions of core and access and then maybe distributions in
there as well.
So remember, it's not just about getting to very large networks. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So remember, it's not just about getting to very large networks.
It can actually scale down as well.
See a set of rules that should never be broken.
The phrase allergy here is kind of intentional.
You should be very careful about question answers that have always or never in
there.
It's not that we should plan to break the rules, but again, collapsing core
distribution
access together or if we have a physical limitation, if we need to connect a
distribution switch
on one building to a distribution switch in another, which then connects to a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
on one building to a distribution switch in another, which then connects to a
core.
Is this allowed by the model?
Technically not.
It's not meant to allow us to just sort of daisy chain all of these network
blocks together,
but at the same time, does the real world require this?
Yeah, the real world does require this.
Maybe I need to spend a bunch of money digging fiber to get this distribution
switch to the
core switch, whereas this connection here by and large works fine.
Is it perfect? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Is it perfect?
No.
Is it what we probably have to expect in the real world?
Yes.
And then lastly down here, three tier core distribution access.
A lot of us might have come into this architectural conversation, expecting to
only talk about
these three network layers because these are the ones that commonly get cited,
especially
when we're first getting introduced into networking.
But the reality is that, hey, we've got a lot more layers and a lot more
network blocks
to talk about now, and so it goes well beyond these three tiers. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
to talk about now, and so it goes well beyond these three tiers.
So D is the right answer.
It provides structure and it provides scale, whether that's scaling up or
scaling down,
but either way, it gives us a foundational set of principles that allow us to
build our
networks in a way that we won't regret down the road.
We don't want to organically grow our networks in such a way that it creates a
massive headache
later when we're trying to do whatever phase comes next.
So here we have an open-ended question.
It's what three layers are used in the campus architecture. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It's what three layers are used in the campus architecture.
The answer here is probably, well, we kind of just talked about it in the last
question,
but it's probably something we're all somewhat familiar with coming into this.
It's the core distribution and access layer.
So when we talk about the hierarchical network model, it has a core block in
the middle, and
then we attach all of these other blocks to the core block.
And so we can be very flexible with how we scale out our architecture, but WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so we can be very flexible with how we scale out our architecture, but
within a site,
let's say over here, this is going to be a campus site.
This campus architecture concept is where we get the core distribution and
access, otherwise
known as the three-tier model.
And so we're going to have a distribution block, which is usually just a pair
of switches
that connect up to the core.
And then we have all of the access switches connecting to those distribution
switches.
Ideally, in a perfect world, we have separate hardware for each one of these WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Ideally, in a perfect world, we have separate hardware for each one of these
layers, the core,
the distribution, and the access.
But sometimes we do have to collapse those layers as we've talked about and
even mentioned
in the last quiz question.
Now something to keep in mind in all of this is what happens if I have another
site over
here.
So this would be another campus site.
It might be all one campus to be clear.
I should probably call this a site over here as well.
We might have one campus with many different buildings, and each building is a
distribution,
type of switch, and we might find that we have to hang some buildings off of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
type of switch, and we might find that we have to hang some buildings off of
other buildings.
But ideally, we do go through some kind of campus core.
And at this point, we see that this three-tier model still applies, but notice
that the
core is shared.
So my three-tier model over here exists, and my three-tier model exists right
here.
And again, that core block is going to be the same core block for both of those
sites.
So just some things to keep in mind as we evolve our conversation beyond the
three-tier architecture WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
three-tier architecture
or the three-tier model and move more to that higher level global view of what
a network
should look like using the hierarchical network model.
So now we're going to talk about a fun concept and something that's going to
come up absolutely
later on in this course when we get to Cisco Software Defined Access and Cat
alyst Center.
But either way, we're going to be talking about access fabrics.
And that is a technology that is, in my opinion, very exciting and a lot of fun WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And that is a technology that is, in my opinion, very exciting and a lot of fun
.
Either way, what is the value of a fabric architecture when compared to a
classic design?
Let's look forward to separate benefits that we can use to justify the
deployment of a
campus fabric architecture.
So generally speaking, what we're going to be looking at here is the ability to
remove
the need for spanning tree protocol and the fact that it scales out to larger
network
sizes.
Unfortunately, the cost of a campus fabric requires layer three switches and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Unfortunately, the cost of a campus fabric requires layer three switches and
there, well, I should
say the architecture requires layer three switches and therefore the cost is
going to be
more.
So we can actually expect it to be a more expensive solution.
It also doesn't reduce complexity.
I would love for it to be a less complex model that gives us all the other
benefits.
But the reality is that deploying standard spanning tree-based switches, that's
pretty simple
even though we don't like spanning tree.
And it is far more complex to run routing protocols and VXLAN. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And it is far more complex to run routing protocols and VXLAN.
And then lastly, eliminating the distribution block, this is false.
We actually do still use the distribution block from a physical perspective.
It's just not going to run the same protocols that it was using or that it was
running in
a standard environment.
So just as a quick reminder of what exactly a fabric architecture is, the idea
here is
that we're going to take our classic campus architecture where we have a
distribution
and access layer like this and we have to decide between layer two or possibly WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and access layer like this and we have to decide between layer two or possibly
deploying
layer three here.
Usually we deploy layer two and this is where we need spanning tree protocol
and all of
these things.
So this is to be our traditional architecture.
But now instead we're going to create a fabric that sort of creates this cloud
that carries
our layer two traffic across layer three.
So now we could draw our access layer switches more in a circle. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So now we could draw our access layer switches more in a circle.
At least that's how I like to do it.
And then you've got this kind of cloud concept because they're all connecting
to an underlay,
which is ultimately still the distribution switches here in the middle.
Or distributions, which is do still exist.
It is layer three out to the edge and we're going to run some kind of routing
protocol
in there to handle this.
And now though we're forming a set of the X land tunnels that carries our layer
two traffic
everywhere.
And so this still allows my laptops here as I draw them out and maybe my WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so this still allows my laptops here as I draw them out and maybe my
printers, etc.
All of these devices can continue to extend layer two to one another as if it
was this architecture
that was extending layer two natively.
So a little bit different and certainly something we're going to be diving into
in a lot more
detail later on.
Again, when we get to software defined access.
But for now, what we really need to understand is just sort of the value of a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But for now, what we really need to understand is just sort of the value of a
fabric architecture
at the access layer and what exactly goes into making it special when compared
to the classic
design.
So this is question number four.
And I did just confirm that there are indeed seven questions.
So just to give us an update, this is sort of the middle question of this group
.
But I do encourage taking a moment to pause the video because what we want to
do here is
we want to map each one of these configurations or features.
And ultimately what we might call functions to either the access distribution WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And ultimately what we might call functions to either the access distribution
or core
distribution or access block.
And what this is really asking us to do is make sure that we know where these
functions
go because we don't necessarily want our core switch providing POE to end users
because
that's not the purpose of the network core.
So just to give away one of the answers kind of, I guess.
And either way, go ahead and pause the video and make sure that you can map
each one of these
features and functions to one of these blocks. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
features and functions to one of these blocks.
So as we go through this together, what we want to do is recognize sort of the
purpose
of each one of these blocks because that's going to help us remember what
functions need
to go aware.
So access, the most important part about the access block is this is where our
users connect.
So anything involving user connectivity should go on the access layer,
distribution is going
to be all about servicing the downstream from a layer three perspective and a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
to be all about servicing the downstream from a layer three perspective and a
layer two
perspective.
So we're talking about spanning tree protocol and FHRP's, that's the kind of
thing we can
expect on the distribution layer.
And this can be the tricky one because sometimes it's hard to know exactly
where a function
goes.
So as long as the distribution layer almost feels like it could go into the
core or access.
Now the core is focused on switching traffic among all of the different blocks.
So we've got other distribution blocks out there. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we've got other distribution blocks out there.
We might have a data center aggregation block.
We might have a WAN block or an internet block.
And the core is designed to connect us to all of those.
So now let's go and go through each one of these functions.
So when we talk about authentication, this is endpoint authentication.
And again, if it has to do with users, this is going to involve the access
layer.
So that's an access layer technology.
Stub routing.
So in a traditional environment, the access layer doesn't do layer two. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So in a traditional environment, the access layer doesn't do layer two.
And as a result, the routing is going to go up here between the core and the
distribution.
So stub routing is used to make our routing table smaller and more efficient.
And so when we're advertising routes up to the core, we want these routes to be
simplified.
And therefore, stub routing is going to be a distribution concept.
And by the way, so is route summarization, since we're on the topic.
Actually, I'll write this over here. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Actually, I'll write this over here.
So route summarization is also going to be for distribution.
It allows me to again, reduce the routing table size of my environment.
QoS tagging has to be at the very edge.
As user traffic comes in, we want to identify what type of traffic it is and
tag it.
So that's going to be access layer.
FHRP's we've just said go in the distribution layer.
That's going to be what allows us to route, not route, but make sure that we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
That's going to be what allows us to route, not route, but make sure that we
have redundancy
among the gateways, which are going to ride on SVIs.
And those SVIs therefore reside on the distribution layer.
So we'll mark that here.
Access layer enforcement access layer access control, ECL access control list.
Got to get my terminology right.
ACL enforcement is going to happen on the SVIs.
And therefore again, because the SVIs are at the distribution block, that's
going to happen WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
going to happen
at the distribution layer.
Full routing is a function of the core.
Again, we want to simplify our routing operation from the distribution layers
perspective, but
the core is responsible for all of this routing and layer three switching.
And so not only is the core doing full routing, but it's also doing that fast
layer three switching
over here on the right.
So SVIs already addressed POE is providing power to end devices.
So that belongs to the access layer.
The ELAN assignment, just like QOS tagging, is going to happen at the edge. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The ELAN assignment, just like QOS tagging, is going to happen at the edge.
We're going to apply a VLAN tag based on which port a device comes in on.
And same thing with the QOS trust boundary, that is an access layer function.
Meaning that if a packet comes in and it has a QOS tag of let's say maybe DSCP
EF, that's
one of the highest, if not the highest priority that we can assign a packet.
Well the question is, do I trust it? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Well the question is, do I trust it?
Because if it's just a PC trying to get prioritized access, we don't want to
trust it.
But if it's a phone, an IP phone, trying to say, hey, I'm carrying voice
traffic, then
we absolutely want to trust it.
So we define the trust boundary at the edge.
And once a packet hits the distribution layer, we shouldn't be asking about
whether we
trust it or not.
We should absolutely be trusting the packets because the access layer already
performed
that filtering for us. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that filtering for us.
So this is a very large list of functions.
And if we're able to go through this and identify where all of these functions
go, that
means we have a very firm grasp of the core distribution and access
functionality.
So sticking with the topic of the network architecture and the hierarchical
model, we want
to look at this diagram and identify the functions served by each block.
Now when we say functions here, I don't mean the functions on the previous
slide that
would take a long time. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
would take a long time.
I just mean hey, is this performing the function of an access block, a
distribution block,
or a core block, or this is a little bit of a hint, or is it multiple, hence
the plurality
there.
So anyways, let's go ahead and pause the video and start to assign these block
functions.
So anywhere that users are connecting, we can expect that to be an access layer
functionality. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
functionality.
This means that these switches here out at the edge are going to be access
blocks, but
the users are also connecting up here, which means that we have access layer
functionality
here at this site.
Now anything that's connecting down to the access layer is going to perform
distribution.
So we are going to perform distribution functions on these switches.
So here at site 2, we see that we have a distribution block connecting to an
access block and over WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
access block and over
here same thing, we have distribution that's going to be needed to connect down
to the access
layer.
Now here's the interesting thing.
We have two distribution blocks connecting to one another.
And so is either of these our core block?
Well if we had just said that, hey, maybe we've got an internet block up here,
it's coming
in over here, that would have clarified things.
But ultimately one of these is going to have to serve as the network core.
And right now, as it's drawn, we could have picked either one. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And right now, as it's drawn, we could have picked either one.
So yes, that means we could have picked site 1 to say that, hey, this is the
core block,
which means that when I do have another block coming in, it's going to connect
over here.
And that does mean that all three functions exist on one set of switch hardware
.
Meanwhile if you had said that the core is going to be over here, that's fine.
It just means that future blocks have to connect here.
So a little bit of an open-ended aspect to the core function, but it is
something for us
to recognize that we're going to want to identify that function based on future WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
to recognize that we're going to want to identify that function based on future
connectivity.
All right, question number six.
And the following benefits describe a layer 2 or layer 3 access layer
deployment.
So when we're looking at these benefits, lower cost infrastructure and point
flexibility,
seamless wireless roaming, this is absolutely the qualities we'd expect out of
layer 2.
Layer 2 comes with downsides, especially spanning tree protocol.
But there's a reason why we see most organizations deploying layer 2. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But there's a reason why we see most organizations deploying layer 2.
It does make it so we don't have to deploy layer 3 switches, which is more
expensive, so it
creates lower cost.
It maximizes our endpoint flexibility because now we can ensure that all of our
devices
can be on different subnet, regardless of if they connect in at different
access layer
closets.
That requirement doesn't come up a lot these days, but if it does come up, at
least we're
prepared for it.
And it doesn't show seamless wireless roaming. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We've mentioned that wireless laying controllers can enable seamless roaming
when we have layer
3 access closet design.
But if we don't have wireless laying controllers, then layer 3 access layer
closets, that's going
to give us a bad time, ultimately, because when I roam from one access point to
another,
and we're connected to access switches that connect in to a layer 3
distribution, at
this point, I'm conducting a layer 3 roam. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
this point, I'm conducting a layer 3 roam.
And that's going to be very painful because I'm going to have to get a new IP
address,
unless the wireless system has some very fancy backend systems to try to tunnel
traffic
around.
Wireless laying controllers kind of fall into that category.
It creates tunnels that allows us to do layer 2 roaming across layer 3
boundaries.
But ultimately, if I want to be sure that this is a layer 2 roam, I should go
with layer
2 access layer deployments.
Layer 3 has the benefit of better scale, and it makes it so that I can WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Layer 3 has the benefit of better scale, and it makes it so that I can
ultimately eliminate
spanning tree.
That's a huge benefit of layer 3, but it does come with some downsides as well,
meaning
that there is no perfect solution to when choosing between layer 2 and layer 3
designs.
All right.
We have reached the last question.
Question number 7.
What protocol is at the heart of access layer fabrics by enabling layer 2 over
layer 3? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
layer 3?
Well the answer here is straightforward.
It is the XLAN.
And one of those questions where we either know it or we don't.
But when we look at tunneling protocols, a lot of them are going to carry layer
3 over
layer 3.
I take a layer 2 frame that has an Ethernet header, let's say, and I strip it
off and
I take this layer 3 packet that remains, and I put another layer 3 header in
front of
it, along with a new layer 2 header, and then we forward it across, and we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
it, along with a new layer 2 header, and then we forward it across, and we
strip these
off, we extract the original layer 3, but notice we have lost the layer 2
information.
Well the XLAN is going to keep that.
It's going to keep the layer 2 Ethernet header information, it keeps the entire
frame,
and then it puts the encapsulation here, we send it across, and once we get rid
of the encapsulation
by de-incapsulating, we're left with the original frame and its entirety. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
by de-incapsulating, we're left with the original frame and its entirety.
So the XLAN enables layer 2 over layer 3, and we're going to see it not only in
data
center, spine and leaf fabrics, but even in campus architectures when we're
looking at
fabric access technology, such as Cisco's software defined access.
[BLANK_AUDIO]