- [Instructor] Networks aren't, or shouldn't,
be built by just grabbing equipment
and plugging it together and hoping for the best.
Network design is the foundation upon which
an enterprise is built.
A stable base is imperative for long-term viability
of any organization.
I'll start small, and in fact, small environments
are often referred to as SOHO,
or small office home office.
These are generally networks of fewer than 10 endpoints
and usually terminates all connections in a single device
that performs all duties.
These all-in-one devices are often layer-three switches
that have wireless capabilities.
A Campus LAN generally refers to a grouping
of relatively close buildings,
all connected together via Ethernet switching.
A Tier 2 Design, as pictured here,
is a LAN that consists of two layers of switches.
At the edge are access switches
that aggregate user machines.
In this example, there are 12 access switches,
each connecting 20 endpoints.
Up from there's a distribution layer.
The distribution layer acts as an aggregation point
for all access switches.
A typical design, as shown here,
has more than one distribution switch
to provide for redundancy.
Tier 2 designs are also sometimes called
a collapsed core design.
This is because in addition to access and distribution,
Sysco also has the concept of the LAN core.
The core is generally the top-level switches
that act as the ultimate aggregation point.
In smaller LAN designs,
the distribution layer also acts as the core.
Examine this tier 3 design.
It shows the access switches and distribution switches
at multiple sites.
Each site's distribution switches then connect
to a centralized switching core which ultimately facilitates
connectivity among all devices on the network.
I'll next jump to some datacenter designs.
A datacenter is a dedicated space in a building
that is designed to house computer and telecom equipment.
A DC generally includes redundant environmental control,
redundant power infrastructure,
and reliable telecom connectivity from providers.
In DC design, we often see a spine and leaf design.
This is similar to the tier 2 design discussed earlier,
but this infrastructure generally has higher capacity,
multiple paths for increased redundancy,
and lower latency.
Next is Wide Area Networks, or WANs.
A WAN is generally a network connection
to an outside network or another network over a distance.
One of the other hallmarks of a WAN is that it is
a leased connection from a carrier or telecom company.
A leased line and a point-to-point connection
are essentially the same thing.
They are private connections between locations
purchased through a carrier.
This can be delivered in a variety of ways.
Layer 2 Ethernet, layer 3 routed links over traditional
public switch telephone networks, or even via wireless.
Traditional PSTN connections are often serial connection
like T1s or DS3s.
These are old standards that require specialized interfaces
to terminate them as they are not
standard Ethernet connections.
The physical connection delivered by the telco will differ
depending on what the local carrier has available
in a given area.
Another example of a WAN is the Internet.
In fact, it's the most-utilized WAN world-wide.
Internet service is generally delivered
in one of several ways: digital subscriber line,
cable connections, Ethernet services,
fiber Ethernet services, or fiber to the home.
DSL is delivered over traditional phone lines,
also known as plain old telephone service, or POTS.
Cable will be delivered over coaxial cable
from the incumbent cable television provider.
Ethernet services will often be delivered
via copper Ethernet cable
in an apartment or office building.
Fiber Ethernet will often be delivered
into office environments.
Fiber to the home is a form of
Gigabit Passive Optical Networking, or GPON.
While this uses Ethernet frames to carry data,
it doesn't work like traditional Ethernet switching,
though this is invisible to the end user.
While speaking about the Internet and WANs in general,
it's a good time to talk about local
or on-premises resources.
If for example you have a local file server in the office,
this would be considered on-prem.
Keeping resources local can lower bandwidth utilization
over the WAN and cut down on latency.
It is becoming increasingly popular, however,
to utilize cloud services
over traditional on-prem resources.
Ultimately, the cloud is just someone else's servers
available over the WAN.
It is highly likely that everyone taking this course
has a free email account from the likes of Gmail or Yahoo
or possibly utilize file hosting on the Internet.
These are all simple examples of cloud services.
It's also becoming increasingly popular to utilize
cloud plot forms to host one's server infrastructure.
By putting services in the cloud,
the underlying infrastructure no longer has to be supported
by an organization, which can save capital expenditures
and the need to maintain data center-like services
to support them.
Server-based cloud resources can often be reached
over the public Internet directly or via
virtual private networks that utilize the Internet
for secure communications.
If only some of an organization's servers live in the cloud,
this company is said to be utilizing a hybrid cloud model
as opposed to a self-hosted or entirely cloud-based model.
The models here, or at least variations of them,
are the basis upon which most of my enterprise networks
have been built for the last 16 years,
and they should serve as a starting point for yours, too.