So let's return one more time to the hierarchical model.
The goal of the hierarchical model is to allow me to expand to as many
different network
locations as needed with the core of the network here in the middle.
But the thing about it, as we've learned, is that we might actually have more
than one
switch in each network block.
And ideally, we're always going to have at least two switches just for the sake
of redundancy.
So if I want to connect to a particular building, maybe a site here on my WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So if I want to connect to a particular building, maybe a site here on my
campus, I would connect
into a distribution block.
I'll put the D here, and then I'm going to have a pair of switches, and we'll
find that
even though I might just from an architectural perspective, draw a single line
and say,
"Hey, the core is going to connect to the distribution."
We know that it's going to have a full mesh, or for that matter, maybe just has
a couple
of connections like this, where we have two fiber connections between the core
and distribution. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and distribution.
So we take advantage of that, we do what we can here.
So we connect our course switches together, we connect our distributions
switches together,
then we have the access layer down here, and this could consist of any number
of access
switches.
And maybe they all have dedicated connections up to the distribution, or maybe
we're going
to have to hang some switches off of other switches.
We'll actually be talking a lot about access layer design coming up here as we
progress
through the network design conversation. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
through the network design conversation.
But while this can represent the campus architecture, one that a lot of us have
probably
seen a lot of information on, it's pretty common to study core and distribution
and access
layers, well, now we've expanded our horizons and realized that we have a lot
of other network
blocks out there.
For example, it might just be something as simple as saying I've got another
distribution
block out here.
So I've got another pair of distribution switches, I'm going to connect those
up to the network WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
up to the network
core in some fashion, I've got another access block down here, and now I've got
connectivity
out to this building, which is itself its own little campus environment.
But from here, we've got all kinds of other network locations to be aware of as
well.
For example, we might have a WAN block, wide area networking, and this WAN
block is probably
going to have a couple of routers in it.
So these routers can connect back to the core as well, and maybe we do full WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So these routers can connect back to the core as well, and maybe we do full
mesh these, however
we want as fine as all layer three connectivity to the core after all.
You can have as many connections as we want and not have to worry about
spanning tree blocked
ports.
But the WAN block is going to allow us to connect out to remote sites that must
connect via
wide area network technologies.
In the case of an overall campus, this distribution block that we drew here is
probably connecting
via some form of fiber, probably single mode fiber to extend the distance that WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
via some form of fiber, probably single mode fiber to extend the distance that
we need to
in order to reach the network core.
But for many of our sites, they'll have to come in via MPLS or some other
technology like
that.
And we're going to bring those connections into these routers and forward them
onto the
core.
And this will allow my users out here at the remote sites to be able to connect
into the
rest of the network.
But it doesn't stop there either.
We might find that we have an internet block. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We might find that we have an internet block.
And the internet block is where things start to get a little bit more complex
as we need
redundant internet designs.
If I just have a single internet circuit coming in, I probably have a firewall
and that firewall
might be redundant.
But ultimately, I'm just going to pass that off to the network core.
But what if I need redundant inbound and outbound internet circuits, where I
have multiple
ISPs that are coming into my organization?
Well, at this point, I might need a pair of routers running at the edge. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Well, at this point, I might need a pair of routers running at the edge.
I might even be running BGP to share routes with my ISPs.
Maybe there are single connections into each router.
Maybe we do have redundancy in there in some fashion.
But ultimately, these routers are going to come in.
And well, in a lot of situations, they'll actually run through firewalls still.
So, my eyes will get those on the drawing.
So maybe we have redundant firewalls here.
And so now we can bring those connections into the network core. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so now we can bring those connections into the network core.
But for larger organizations that have these more complex internet needs, hey,
this internet
block is going to be a really good idea.
And for that matter, then at the end, we can still talk about our data center
infrastructures.
And we might find that one of our data centers is running the traditional
aggregation and
access model at which point our aggregation switches are just going to connect
into our
core switches, probably redundantly at layer three. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
core switches, probably redundantly at layer three.
Redundancy matters even more inside the data center after all.
Or we might find that we have a data center fabric.
And that data center fabric is going to run spine and leaf architectures.
And this will look a little bit different.
As our core switches actually connect in via the leaf switches in this case.
And that's because of how the fabric comes together.
And so either way, whether we're running a fabric or a traditional aggregation
access
model, we're going to find that our data centers are going to connect in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
model, we're going to find that our data centers are going to connect in
through the core.
And on top of all of that, we might have even more distribution blocks or we
might find
that we need additional wind blocks for scaling.
And regardless of which blocks come next, ultimately, I can still connect that
into the network
core there in the middle.
And I can continue to scale my network out to greater and greater sizes.
It's all thanks to mapping back to this hierarchical network model. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It's all thanks to mapping back to this hierarchical network model.