Overlay networks have really become our go-to for creating better network top
ologies.
As we've said before, an overlay network is sort of the network that I want
when I don't
have it.
What I have is an underlay network.
And so this might be a situation where we've seen that we create an underlay
network that
consists of maybe a layer three world.
So maybe I've got layer three between a bunch of devices, but I really want
layer two.
And so I create a layer two overlay over that underlay or possibly just a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so I create a layer two overlay over that underlay or possibly just a
different logical
architecture.
So whatever this underlay ultimately looks like, you can have all kinds of
different
hops in here and different network paths and so on and so forth.
But if I create a tunnel from this device to this device, well, now these two
devices
are directly connected and they can directly share a GRP and OSPF routes.
And so if I want these two devices to be effectively connected to one another WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so if I want these two devices to be effectively connected to one another
via layer
three, well, that's where I create that overlay of what I want.
Now we're called a long time ago where we discussed the concept of access layer
fabrics.
We are finally going to bring this all back around because we have talked about
LISP and
now we're going to be talking about VXLAN.
And the reason why we're talking about these technologies and why they show up
on this
exam blueprint and inside of this course is because of access fabrics being an WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
exam blueprint and inside of this course is because of access fabrics being an
important
part of enterprise network design.
And so we've talked about LISP and again, we're going to talk about VXLAN.
But in order to really understand what VXLAN is trying to accomplish, it helps
to know
where it came from and why it was developed.
And the answer to where it came from is once again, the data center.
The data center kind of keeps coming up in these network conversations, even
though this
is on core.
And yes, there is a data center core exam, DC core. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And yes, there is a data center core exam, DC core.
And hey, guess what?
We have that content available on our website here at CBT Nuggets.
But at the same time, even though we say, well, data center technology should
really
be in its own, maybe a pillar of network architecture, at the same time, the
data center
is part of our network design.
So we think back to the hierarchical network model where we've got the core of
the network
and we know that connects to a distribution block, which connects to our access WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and we know that connects to a distribution block, which connects to our access
.
We've got all kinds of different blocks in here.
And one of the important blocks is the data center aggregation, which leads to
the data
center access layer.
So this whole thing over here is our data center.
Why is the data center so important?
Well, again, we have two things that we host in the data center that are
mission critical.
Number one is our applications.
And it's really hard to run most of our organizations these days if we have no
access to our applications. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
access to our applications.
Not a lot we can do with pencil and paper if we don't have access to what we
need on
the computers.
But the second thing we host is our data.
Whether that's files and just file servers or maybe even intellectual property,
the massive
amount of storage and data that we run in data centers and now run analytics
against
that data, that is all mission critical for our organizations as well.
And so because of the fact that this is so important to our organization, the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so because of the fact that this is so important to our organization, the
data center
is considered a highly critical environment.
Now when we think of a classical data center architecture, there is strong
parallels between
the data center, this traditional classic architecture and what we did on the
campus
side.
So we really relied heavily on the same three tier architecture.
The idea here was that we'd have a core network block and I would create that WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The idea here was that we'd have a core network block and I would create that
aggregation
block.
So let's just do a pair of aggregation switches.
And remember the aggregation is very similar to the distribution block on the
access layer
or on the campus side.
And so the idea here is that we're going to connect up via layer three to our
core network,
over the core of our network.
And then we also have an access layer down here.
So we've got lots and lots and lots of these access layer switches. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we've got lots and lots and lots of these access layer switches.
And then we're going to connect down here all of our devices.
Now our devices in the data center look a little different than our campus.
We don't have phones and access points and said we have servers, we have
storage arrays,
we have appliances, we have all kinds of things in the data center that we don
't really see
a whole lot of in the campus.
And vice versa, we don't see campus things inside the data center.
Very different use cases.
But we do see that this strongly parallels having a distribution and access
block like WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
block like
we're used to over on the campus side.
So the thing about data centers is that we require layer two everywhere.
And we say that we like layer two on the campus side, but we can sometimes get
away with layer
three out to the campus access layer because layer two isn't really necessary
in a lot
of situations outside of maybe printers that need to communicate with one
another, something
like that.
But in the data center, this is mission critical. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But in the data center, this is mission critical.
We have to have layer two between our servers and our storage especially, but
then some
appliances and softwares, they also require layer two among each other.
And so we need layer two everywhere, which is fine because we built this out
with layer
two.
Now, I say fine, but we still have to worry about things like spanning tree in
this topology.
We have to worry about first-to-part redundancy protocols and all of the same
things that
we have to worry about on the campus side.
There's one of the reasons why we want to go to a campus access fabric rather WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
There's one of the reasons why we want to go to a campus access fabric rather
than having
layer three or layer two everywhere and having to decide, we go with something
like a fabric,
which is, hey, where we're going with this whole conversation as well.
Well, when we move over to or when we realize that we run out of space on the
aggregation
layer, we can't just add a third switch because of spanning tree protocol,
because of first-to-part
redundancy protocols, because of physical connectivity concerns, this third WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
redundancy protocols, because of physical connectivity concerns, this third
switch concept
doesn't really exist.
But we can't just keep building up and building up aggregation switches.
It's going to be port limits and throughput limits on those.
So what we do in the data center, again, the classic model, is we bring this
together and
we refer to this as a pod.
And so from here, we can build another pod.
And so we've got a pair of aggregation switches over here. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so we've got a pair of aggregation switches over here.
This is layer three to the core, and then we've got our access down here, and
it's all going
to be built out the same.
What's the problem with this?
Well, the problem with it is that even though we've got layer two everywhere
here on the
right on this pod, we've got two different pods now, we see that we have layer
three
segmentation through the network core.
So if this storage array needs to be accessed by this server, we're going to
have to have
layer three segmentation, which causes a lot of problems. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
layer three segmentation, which causes a lot of problems.
So this concept of a three tier model and the scaling out via layer three that
just
doesn't fit very well with our data centers.
So there's two problems here.
First of all, it's just the layer three segmentation.
But second of all, another problem starts to occur as we build out these very
large
layer two spaces.
Because what we might start to do is say, okay, well, we're just going to make WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Because what we might start to do is say, okay, well, we're just going to make
the aggregation
layer as large as possible.
And we're just going to deal with the pain points of having to scale this up as
much as
we can, but we don't want to create another pod.
The other problem we start to run into is that our VLAN identifiers, that 4,000
is too
much.
We need more than 4,000 or 4K here, we'll say, more than 4,000 identifiers.
The reason for that is we want to keep our broadcast domain small, we're WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The reason for that is we want to keep our broadcast domain small, we're
deploying small
VLANs everywhere, but that starts to add up.
And this is especially true in the service provider space, because they
typically will
assign multiple VLANs per customer.
And as they scale up to potentially even just a few hundred, let alone like a
thousand
or 2,000 customers, we do start to run out of VLANs very, very quickly.
So what's the solution to all of this?
Well, the solution is to create a combination of two different technologies,
the first of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the first of
which is that spine leaf architecture.
And we've talked about some of this, I understand some of this is review, but
again, it's important
to really understand where we're coming from here.
So the spine leaf architecture changes this classic notion to say, hey, instead
of building
it out such that we have to rely on layer three, let's go ahead and flip things
around
a little bit and try to create more of a backbone centric architecture.
What exactly does that look like? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
What exactly does that look like?
Well, what we're saying here is that we want to have our, if we want to think
of it, our
more aggregation level switches, all we really want them to do is switch
traffic between the
leaf switches.
So you build out your spine and leaf architecture and spines connect to leaf
switches, leaf
switches connect to spine switches, but we do not connect all of these switches
together.
Leaf switches don't connect to leaf switches.
Spines don't connect to spines. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Spines don't connect to spines.
And all of these, by the way, are layer three leaks.
And so the idea here is to enable very fast switching from one of these leaf
switches to
another leaf switch.
And furthermore, because it's layer three, we can scale out to potentially
hundreds of
leaf switches, I mean, the scale of this is absolutely enormous.
We're more limited by physical limits, such as ports on the spine switches, as
well as
just fiber in the data center.
And what's interesting about this is that because of that, these switches in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And what's interesting about this is that because of that, these switches in
the spine
layer are a little bit more dumb, meaning all they care about is bringing a
packet in
and sending that packet out.
They're not responsible for things like spanning tree roots and FHRP and
running all of these
protocols.
They are focused on switching packets.
That's all they really care about.
So not only is this highly scalable, which is a huge improvement over the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So not only is this highly scalable, which is a huge improvement over the
traditional
architecture, it's also highly consistent.
There's kind of an interesting side effect to this that every single device is
exactly
two hops away.
So if I have a server over here and a storage array I want to communicate with,
well, that
could be here, it could be here, it could be all the way out here.
And it doesn't matter because I simply have to send my packet up to one of
these spine
switches. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
switches.
That's hop number one.
And then hop number two is to get down to the remote leaf switch.
And there we go.
I don't have to worry about possibly going one, two, three, four, five hops or
one, two,
I guess that would still be two hops within the same pod.
So we don't have to worry about those inconsistencies anymore.
It's far more consistent and that creates much better network performance.
Well, we still have a problem. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Well, we still have a problem.
And we already said that we need this to be layer two everywhere.
And we've gotten rid of that because of the layer three.
Well, where do we get the layer two from?
And that is the second technology, which is VXLAN, which allows us to deploy
layer two
over layer three.
So now I can form a VXLAN tunnel from one of these leaf switches over to the
other leaf
switch or actually let's say we're communicating to one of those storage arrays WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
switch or actually let's say we're communicating to one of those storage arrays
.
So now I create a layer two tunnel and that carries the entire ethernet frame
and through
the layer three infrastructure and allows these devices to be layer two
connected.
Furthermore, we're going to find that VXLAN identifiers solve this problem over
here
on the right where we're running out of VLAN IDs.
As we've said before, VXLANs allow up to 16.7 or so million identifiers far WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
As we've said before, VXLANs allow up to 16.7 or so million identifiers far
more than
the 4000 we get with VLANs.
It really comes down to this being 12 bits versus 24 bits for the XLAN.
So the spine leaf in the XLAN architecture, this is where the data center is
being built
out today and how it's being built out today.
But this VXLAN technology, it's starting to be used outside of the data center
as well.
And so we're seeing it actually being deployed into these access fabrics that
we deploy on WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we deploy on
the campus side.
So this is why we're studying VXLANs.
It's important to know where it came from and why it matters so much and what
exactly
it's accomplishing, namely this layer two over layer three via tunneling
mechanism.
But at the end of the day, what we're really going to apply this towards within
the world
of enterprise networking is seeing that it also enables us to be able to create
these
access layer types of fabrics.