Well, it's time to start thinking big because up until now, we have focused on
what's known
as a single hop type of fabric, which is going to be what we deploy in the
majority of our
corporate networks.
The idea is that I deploy an edge to one site and I deploy an edge to another
site.
And as we've drawn out so many times at this point, we've got a couple of wind
circuits
in here.
And we're going to form tunnels directly to one another.
So IPsec tunnel here and IPsec tunnel down here.
So that works out great other than what happens if we start to think again
bigger globally.
What happens if this edge device is in Eastern Europe, let's say it's in Poland
and the
edge device on the left here, this is on the west coast of the United States.
So let's say it's in California, so the US West coast.
Geographically, these two devices could probably not be much further apart.
We're traversing half of the globe and even though from an overlay perspective,
this looks
very simple.
I'm just connecting from one edge to the other.
But we know that there's an underlay happening here.
So what does the underlay look like?
How many routers?
How many devices are we going to go through?
And it's easy to say, well, just, you know, we should make this better somehow.
Except we still have to take an underlay.
We still physically have to get from one router to the other.
So what more could we do?
I mean, we might resign ourselves to just say, you know what, the global
internet's the
global internet.
And I'm just going to have to rely on it and use it to get from one side to the
other.
Now naturally, if we're using a WAN circuit or service provider like MPLS,
things might
change a little bit, but it's still worth having a conversation to see how they
build
out their underlay in this situation.
So next up, we say, you know, let's not be content.
Let's figure out a way to improve this.
And this is going to lead to the conversation around multi-region fabrics,
which is an architecture
that Cisco devised.
And sometimes we abbreviate these as MRFs.
And again, we're trying to enable things globally.
When we look at the single hop architecture, we could think of this as a flat
network.
We're essentially just moving going from one edge device to another edge device
, potentially
in a full mesh or partial mesh topology.
But there's no hierarchy here.
Every edge device just connects to every other edge device.
With the multi-region fabric, we're going to change this a little bit.
We're going to build a hierarchical network, something that is no longer flat,
sort of
like how when we went from flat networks to hierarchical networks with
distribution layers
and such, we're going to do the same thing now with our SD-WAN environment.
So here's the idea.
I am going to build a core network.
And this core in my SD-WAN, so I'm going to call this my SD-WAN core here just
to clarify,
this is not my network core, this is my SD-WAN core.
And I'm going to deploy, let's just say I deploy, let's deploy four routers for
redundancy
here.
And so I'm going to make sure that we've got good connectivity among these four
routers.
What I'm going to do is attempt to make it so that this is geographically
centered as
much as possible based on my organization.
And so from here, I'm going to divide the rest of my network into region.
So let's say I've got region one on the left, maybe this is the US in this
situation, and
I've got region two over here, and we'll call this Europe.
So now we've got two different physical geographic regions involved.
So what are we going to do?
Well, let's say I deploy, we'll just keep this simple.
Let's say I deploy three edge devices over in region one, and we deploy a
couple over
in region two.
Normally, we'd look at this and say, okay, well, we're going to make sure our
IPSAC tunnels
get built out.
We'll just do one circuit here.
I'm not going to draw two circuits.
That's going to make things really complicated.
But let's just say we do our full mesh on the left.
Well, normally we would do a full mesh over here and we'd be doing this kind of
thing
and it would get really complicated.
And again, we're forming IPSAC tunnels over very long distances.
Instead what we're going to do is we're going to form relationships with the
cores that exist
in our regions.
So maybe these two devices are close to region two or maybe even in region two.
These two devices are going to be close to or inside of region one.
So now what we see here is we formed full meshes.
However, we've done so with a hierarchy in mind.
And we do see that there's this second layer that exists sort of above the edge
layer.
So to be clear, I am forming my edge to edge connections within a region.
That's going to be the first big thing and it's important that we recognize
that.
We are also forming relationships to the core.
However, we're going to factor in our region and we are not any longer forming
relationships
with the edge devices between the two different regions.
Now we have to ask ourselves what is the value of this?
We're building a bunch more tunnels.
However, aren't I still taking whatever internet pathway exists or are we doing
something more
special?
Well, the answer here would be that this is only valuable if we're doing
something more
special, specifically that we're going to need some properties from our core in
order
to fully justify this.
Specifically, we are expecting that we're going to have some very high
bandwidth connections
between our core devices.
So we want to make sure that we're built on essentially the super highways of
the internet.
Rather than relying on whatever lower cost links there might exist out there,
we're going
to pay a premium for much higher bandwidth connections.
So if this truly is between the US and Europe, these would be transatlantic
connections.
Well, do we want the lower end lower bandwidth ones?
Or do we want to pay for the higher end, higher quality ones that are more
likely to
be there and operate fully?
And so what we're going to find is that there are service providers in the
modern internet
that like to provide this.
For example, our cloud service providers are one and we also have another type
of provider
that's worth noting.
And these are known as software defined cloud interconnect providers or SDCIs.
We'll be talking a little bit about these when we study on-ramp in the next
skill.
But either way, these providers have built out an infrastructure such that
everybody in
the world should want to be able to connect to them at a really good high
bandwidth experience.
Because if I'm going to be performing, for example, connectivity into a cloud
space, I
need really good connectivity.
I don't necessarily just want to take standard internet circuits to get there.
So we have these concepts of building much higher bandwidth and lower latency
connections.
And that's exactly what we build the SD-WAN core on.
And then we rely on the standard infrastructure in order to get us out to the
edges that belong
in each region.
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