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Imagine you were hired to build a network for a small startup company. What

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would that network look like?

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Well, we're probably going to bring in the internet here

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And so we're going to need some kind of edge router or firewall

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And then we're probably going to connect into a handful of switches. Maybe we

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've just got a

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Primary switch here in one of the access closets for our users to connect to

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and then we've got another switch over here

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Maybe in another part of whatever space we're leasing and that will connect to

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the rest of the network

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And from there we might even want to connect a few access points for wireless
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And from there we might even want to connect a few access points for wireless

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connectivity

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So this would be the extent of the network, but guess what this particular

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startup company is going to expand and grow very quickly

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And so they're coming to you now and saying hey that network you designed it

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needs to be bigger. We need more

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wired connections

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So I'm gonna scale out here my

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My switches we're going to take over another part of the least building. We're

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going to need another switch out there

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We're going to need more access points and eventually we start to create a
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We're going to need more access points and eventually we start to create a

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network that looks like it's kind of a mess

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This is the concept of organically growing out our network and it starts to hit

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some big concerns

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For example, what about the redundancy in this network design?

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What happens if the internet goes down? What happens if this one switch right

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here?

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Where to fail the entire network would lose access to first of all the internet

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and

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Second of all this section of the network wouldn't be able to talk to this
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Second of all this section of the network wouldn't be able to talk to this

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section of the network if that's even

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valuable with the internet being down in many cases. It's not we might need

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some my some number of servers to run our

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applications

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So we might have some kind of sales or

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Sales type of application that we want our sales folks to have we might have

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engineering applications

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Whatever that looks like we're going to need to put some servers and

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Some maybe storage arrays out on the network
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Some maybe storage arrays out on the network

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But where exactly does that go?

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We've pegged this switch for that

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But does that really make the most sense for it to be there?

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Especially if we also have laptops and other PCs hanging off that same switch

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What happens when we introduce a whole other site?

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All together so now we have site two and we're going to have some kind of

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router there and a switch for the local users

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How do I connect this network into the rest of the network that I'm building
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How do I connect this network into the rest of the network that I'm building

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out?

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So this is a concern and again organically growing out a network can be painful

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It would be a whole lot better if we had an architectural model

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Well, fortunately we do have an architectural model. We're all here to talk

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about the hierarchical network model and

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The hierarchical network model is intended to give us a set of guidelines

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That's going to help us to build a network out to achieve some of these
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That's going to help us to build a network out to achieve some of these

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concerns

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For example, we do want to focus on redundancy giving us a redundant design

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But importantly and something that we didn't add to the list down here. We

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probably could and

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Should is

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Scaling we want to be able to address the need to grow it worked out fine when

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our network was this big

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The original network that we deployed for a very small set of users

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But as we grew we started to see that just throwing a couple of switches out
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But as we grew we started to see that just throwing a couple of switches out

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there with a router was

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Not something that was intended to grow beyond its original scope

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So we need something that allows us to grow and add and expand and we're not

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just talking about

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local users

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But we're also talking about

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Different sites. We're talking about maybe even bringing in more redundant

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internet circuits

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So we need to consider the internet in this

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We need to consider the wide area network this connection right here that's
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We need to consider the wide area network this connection right here that's

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going to connect my site to

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Into site one and for that matter where are we going to put those servers?

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That are running the applications and storing the data for our users so that

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they can do their jobs

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The goal of the hierarchical network model is to show us how to get all of this

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Using a blueprint that is going to be a starting point the idea here

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Is that we don't want to get stuck we want to have a starting point and be able
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Is that we don't want to get stuck we want to have a starting point and be able

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to grow as much as possible or as much as needed over the course of time

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And what we're going to find is this model ends up giving us a building block

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type of architecture

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We think back to kindergarten and having different building blocks being able

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to just put a block down and put another block here

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And maybe I put another block next to it and I stack it up and make a tower the

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idea of this building block type of architecture is to say that each one of
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idea of this building block type of architecture is to say that each one of

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these

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Could be a different part of the network and I just need them to be able to be

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inserted or removed

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Depending on the current network needs here's what this looks like from a

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network perspective

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We want some kind of network core that sits in the middle of our network a lot

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of us have studied

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The core distribution access layer types of models. Those are part of CCNA

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studies and now it's time to get a little more detailed
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studies and now it's time to get a little more detailed

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Because the core of the network isn't just a layer. It is a block

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Again, this is part of the building block architecture which is intended to

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allow us to scale out

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So what if I do want to have a core distribution and access layer type of model

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?

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Well, no problem. I'm going to build a distribution block

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And I'm going to connect the distribution block into the core block

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And then I know that my access block is going to hang off of that distribution
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And then I know that my access block is going to hang off of that distribution

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block and

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So far this doesn't look a whole lot different than anything else that maybe we

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've studied in the past

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However, now let's start to scale this up

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Beyond what a single site would look like because I might have another site

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that is a second distribution block

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That also has an access layer

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I'm going to want to connect up into an internet block up here as well as a

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wide area network block

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And for that matter, I probably would want to start thinking about these
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And for that matter, I probably would want to start thinking about these

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servers and connecting to some kind of primary data center block as well

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And for that matter, maybe we want a backup data center

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And so as we zoom out and we look at this network design, this is going to look

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a little bit like a hub and spoke

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I guess I so wrote spoke first

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Hub and spoke or spoke in hub type of topology

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I'm going to put this in air quotes because when we talk about a hub and spoke
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I'm going to put this in air quotes because when we talk about a hub and spoke

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from the perspective of network

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Architecture usually what we're talking about is a switch that connects to

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another switch up here and another switch down here

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But we're not talking about switches here

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We're talking about blocks

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Our different

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Building block architecture here is going to allow us a number of things first

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of all anytime

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I want to add another block

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I simply have to deploy the block and connect it into the network core
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I simply have to deploy the block and connect it into the network core

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Yeah, my drawing is really pretty with exactly nine blocks here

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But I just added a tenth block and from an architecture perspective

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I just did with this block what I did with all the other blocks

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This might be as a completely new site site number three

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And it's another distribution block that's going to plug into the core

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I can do this as many times as needed because the purpose of the core is to

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serve as that hub

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Which is going to connect all of the different network components together
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Which is going to connect all of the different network components together

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Or all of the different places in my network should be able to reach one

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another through the network core

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So this is an expansion of what we might refer to as the enterprise campus

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model

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Which is something that we study a little bit more off and that involves once

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again the core

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distribution and access layers

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And we're going to be drilling into the details of what this looks like as well

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But it is important for us to recognize that there's a lot more places in the

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network than just the core distribution and access
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network than just the core distribution and access

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We have needs for other network locations

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And if we try to build out a network organically like this and just keep

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feeding one switch off of another

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And deploying things on an as needed basis

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Then this is going to fail from a scaling perspective

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And we compare that to this modular architecture

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Which allows us to both add blocks and remove blocks on an as needed basis

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Well now we can truly scale up our network
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Well now we can truly scale up our network

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Starting with something very small with the current needs

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And being able to grow our network to enterprise level and even global

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Corporation type of level using this model