The hierarchical network model is a great model. It's one that we absolutely
want to use
for the foundations for our network designs. But notice that our focus for why
the hierarchical
network model is so important is because of scale. The larger our network gets,
if it's built on
the foundational principles of the model, then we're going to have no problem
scaling out.
But things get a little bit interesting when we scale back in. Specifically,
when we're looking
at smaller networks, and we realize maybe the hierarchical network model doesn WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
at smaller networks, and we realize maybe the hierarchical network model doesn
't fit. Or is that
even maybe not the best way to say it? Let's take a look at an example here.
Let's say that we have
a small network. So we've got a small, we'll call it a headquarters site, but
maybe it's just a small
company. Just getting going here. And we have a couple of access closets. And
so we'll call these are
access layer switches in here. So we've got a couple of switches in each access
closet. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
closet.
And then we're going to connect those back, according to the model, to a pair
of distribution
switches. So here's our distribution model here. And then we know that we've
also got an internet
circuit coming in. So here's the question, how would the model suggest that I
build this out?
Well, the model would say, hey, we've got maybe a pair of firewalls up here.
And we're going to bring
those into a set of core switches. So we bring those into the core switches. So WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
those into a set of core switches. So we bring those into the core switches. So
this is the core.
Now we have distribution down here. And we connect all of these together like
we said that we would.
And now we have our network built. But here's the big question. What on earth
is the value of the
core switches here? All we're doing is taking our internet traffic and forward
ing it down to the
distribution layer, whereas we could have really just brought that internet
circuit directly into
the distribution layer. So is the core doing anything? Is it worth having in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the distribution layer. So is the core doing anything? Is it worth having in
the answer is no,
no, we'd probably be better off without having the core layer. So what we might
do is revise our
network design here. And we'll say, all right, we still have those access clos
ets. We still need those
access switches. And then we'll put a pair of probably pretty small
distribution switches here
that are going to connect down. So this is still our dist layer. And then our WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that are going to connect down. So this is still our dist layer. And then our
internet circuit is
coming into a pair of firewalls. Draw these a little bit bigger now. And so we
've got an internet
circuit coming in probably redundantly in some way into these firewalls. Maybe
it's a high
availability pair. But either way, we now can connect these into the
distribution layer. And now this
is a much cleaner network model. Or maybe I should say it's it's right sized.
Again, doing network
designs, there's always this sense of trying to find the balance between what WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
designs, there's always this sense of trying to find the balance between what
the right type of
design is for a particular organization. And also maybe what something like the
hierarchical model
is trying to tell us because the hierarchical model says, Hey, we need a a core
layer or a core block.
And I'm looking at this saying, Hey, I'm maybe consulting or maybe this is my
organization. And I'm
trying to go and justify switches that cost multiple thousands of dollars to WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
trying to go and justify switches that cost multiple thousands of dollars to
just sit there as a
core layer. It doesn't make sense. So we have to adapt our model and we have to
figure out a couple
of things. First of all, what is the right size for this network? We want to
make sure that we're not
you building something that is way too big and way too expensive that this
company doesn't need.
But at the same time, we need to ask ourselves, Okay, but what about that whole
scaling concept? Because
I our company is small, but we might well grow. So am I setting myself up for WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
I our company is small, but we might well grow. So am I setting myself up for
failure by in some way
violating the model? And what we're going to find is that we're not actually in
violation of
anything here. We are adhering to the model, even though it doesn't look like
it quite at first.
So what did we do here? Why can we say that we're adhering to the model? Well,
first of all, we see
that there are a dedicated distribution block. We have our access block down
here. We have our
internet block up here at the top, but we don't have a core layer or do we? See WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
internet block up here at the top, but we don't have a core layer or do we? See
, when we build out the
hierarchical network model, the model appears to be a physical model. We use
that building block
concept. I put the core in the middle and I connect it out to all of these
different blocks. And we
want to make the assumption that each one of these blocks is a physical set of
switches. So I've got
switches in here and pair of switches and all of this is a physical model. But
this isn't necessarily WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
this isn't necessarily
true. Instead, the model isn't really focused as much on the physical, but on
the logical. And specifically,
the word I like to use for this is function or functions. We'd spent a lot of
time breaking down the
functions of the different layers, especially as it relates to the access layer
, the distribution
layer, the core layer, wherever that is up here. Core distribution and access WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
layer, the core layer, wherever that is up here. Core distribution and access
all have very
different functions. But notice that in our case here, we don't have a physical
core layer. And so
is that a problem? Well, not really, because we actually do have core
functionality here.
What's the core supposed to do? Fast layer three switching. What are these
distribution switches do?
They're performing fast layer three switching between the internet block up
here and the access
blocks down below. So we do have core and distribution functions happening, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
blocks down below. So we do have core and distribution functions happening,
even though it's a,
they're sharing a single pair of switches. So again, not focused on the
physical, we are focused on
the functions, the logical side of the model. And in that sense, we absolutely
are adhering to
the hierarchical network model, even for this smaller network design. Now,
certainly in a perfect
world, each of these logical functions would map to a physical set of switches WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
world, each of these logical functions would map to a physical set of switches
that are dedicated
for that purpose. And for large at scale networks, we absolutely should be
doing that. But this concept
of placing multiple functions into the same physical set of hardware has a word
that we use often
in this industry and it's known as collapsing. So in this case, we would
especially refer to this as
a collapsed core design, where we don't have a dedicated core. Instead, we have WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
a collapsed core design, where we don't have a dedicated core. Instead, we have
collapsed
this word collapsing here. We have collapsed the core functions into the
distribution switches.
Or I guess you could argue that we collapse the distribution functions up into
the core, but
usually we go sort of a top down approach when we're talking about this.
The way I like to refer to this is not just saying collapsed core, but we might
say it's a collapsed
core and distribution layer. So however we want to word it is fine, but when we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
core and distribution layer. So however we want to word it is fine, but when we
are referring to this
no matter what, we are going to refer to it as being collapsed. And so we can
take one physical set of
devices and give it multiple functions using this collapsing method. Now,
collapsing doesn't have to
stop there. We don't necessarily just stop with the idea of collapsing our core
and distribution
blocks together. Let's imagine a site that has 10 employees. What kind of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
blocks together. Let's imagine a site that has 10 employees. What kind of
network does this site need?
Well, if I truly try to adhere to the model, we're going to have way more
hardware than we ever
needed if we're mapping each function to physical sets of hardware. But even if
we build out a
network like this over here, this is overkill because we only have 10 employees
. And by assumption here,
we're saying that we have roughly 10 devices. Maybe we have some wireless WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we're saying that we have roughly 10 devices. Maybe we have some wireless
devices in there.
But ultimately, we don't need a ton of connectivity. So how would we build out
this network?
Well, probably we have some kind of internet circuit coming in to a firewall.
It's probably not
even redundant for this little site. And then we could have a single switch and
all of our users and
all of our phones and all of our access points could all connect into a 24 or WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
all of our phones and all of our access points could all connect into a 24 or
maybe 48 port switch
if we have enough extra devices in there. And then we just connect the firewall
up.
So does this add here to the model? And technically the answer once again is
yes. This does add here
to this model, but not from a physical perspective, yet instead from a
functional perspective,
we would say that it does. Because at this point, what we've done is we've
created a collapsed
environment. And we have created a single switch here that is a collapsed core, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
environment. And we have created a single switch here that is a collapsed core,
distribution,
and access switch. It's performing all of the functions. We have connectivity
from an access
perspective here. We're creating the connectivity. We're assigning VLANs,
potentially doing QOS tags.
We have SBI's on this switch. And we're not running first-top redundancy
protocols because
we don't even have a second switch. But we do have the SBI's. We are creating WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we don't even have a second switch. But we do have the SBI's. We are creating
the functionality
that the distribution performs. And then the core functionality is simply
switching back and forth
between the firewall and the users. And so yeah, it's a single switch. And yet
it adheres to the
higher, higher article network model. And I suppose we might even call this a
one-tier model.
Whereas before over here with our collapsed core and distribution plus our WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Whereas before over here with our collapsed core and distribution plus our
access,
this would be more of a traditional two-tier architecture. Now ultimately, even
though probably
stretches a little beyond the scope of this course, if we're thinking about
being network
architects or studying network architecture, a big part of designing networks
is staying flexible.
We want to stay flexible because we need to find a balance between the spend of
a network. In other
words, how much does this network cost? And compare that to really just having WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
words, how much does this network cost? And compare that to really just having
structure. So adhering
to this model. There was a time when my brother actually gave me a call. He was
looking at starting
up a company and he asked me for a quote and he decided, "Hey, not necessarily
a quote." But he asked
me for a budget. Like, how much should I expect to spend on a network for this
site? And because it's
my brother and I just like messing with him, like he likes messing with me, I
sent him a quote for WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
sent him a quote for
$150,000 worth of equipment. And after laughing a little bit, we had to start
having more real conversations.
But a small startup company probably just needed a small network switch in a
firewall,
not $150,000 worth of gear. And so it is always a matter again from a design
perspective of saying,
"I know what I'm trying to do. I'm trying to do this model. I'm trying to make
it so we can scale up." WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
it so we can scale up."
But as long as we are adhering to the principles of the model and making it so
that we can scale up
one day, then we're going to be in good shape as long as we're considering all
of these principles.
So that's certainly one of the takeaways from this conversation. But when we're
saying flexible,
we need to think about all of the things. We need to think about the fact that
we might deploy this
one-tier model. We might deploy a two-tier model where core and distribution
are collapsed. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
are collapsed.
We might actually have a situation where we collapse our distribution and
access together. So
what happens if I have a distribution switch and I have access switches out in
access closets?
But inside of this distribution closet, I also have runs that are going out to
the floor where
users are going to connect. Does it make sense for me to deploy dedicated
access switches for those
users? Or can they just come into the distribution switch? At that point, this
would be a collapsed WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
would be a collapsed
distribution and access block. And so these are the kinds of ways that we can
leverage what we
simply call a two-tier architecture. But ultimately, it comes back to saying we
're going to leverage
the collapsing of these different functions together, not necessarily lock
every single
function to a physical set of hardware. And again, try to strike that balance
in order to make
sure that we're not over-sizing networks for the need.