In the previous lesson we inventoried the network of Grupo Meridiano and ended on an important observation: the Valencia office network, the Bilbao branch network and the Internet are not "networks" of the same type or the same size. In this lesson we will bring order to that intuition: we will learn to classify networks by geographic reach (PAN, LAN, WLAN, MAN, WAN), by the relationship between their machines (client-server versus peer-to-peer) and by who is allowed to access them (private versus public). We will close with a concept that solves a real problem for our company: how to securely connect the Bilbao branch to Valencia across the Internet using a VPN. Mastering this classification is essential: each type of network has its own equipment, its own costs and its own problems, and a professional must know at all times "which type of network they are in" when designing or troubleshooting.

1. Classification by geographic reach
2. PAN: the personal network
3. LAN and WLAN: the local area network
4. MAN: the metropolitan network
5. WAN: the wide area network
6. Classification by relationship between machines: client-server vs peer-to-peer
7. Private networks and public networks
8. VPN: a private network over a public network
9. Case study: the network map of Grupo Meridiano

The most common way to classify networks is by reach: how much territory they cover. It is not an arbitrary classification: reach determines which technology is used, who owns the infrastructure and how much it costs.

A simple mental rule: the greater the reach, the less control you have over the network. Your LAN is yours end to end; on the WAN you depend on carriers, contracts and equipment you will never lay eyes on.

A PAN (Personal Area Network) connects the devices of a single person within a radius of a few meters: phone, headphones, smartwatch, wireless mouse and keyboard... The star technology here is Bluetooth, though NFC (phone payments) or a USB cable between phone and laptop also count.

Key characteristics:

• Minimal reach: usually under 10 meters.
• Few devices: one person's worth.
• Trivial setup: pair and done; no professional administration required.

It may seem anecdotal, but the PAN shows up in daily work: when a Grupo Meridiano consultant shares his phone's data connection with his laptop at a client's premises (tethering), he is creating a small PAN that also provides a way out to the Internet.

The LAN (Local Area Network) is the type of network that will keep an IT professional busiest: the network covering a limited space under a single administration: an office, a floor, a building, a home. Everything we inventoried in Valencia in the previous lesson — the 20 PCs, the file server, the printer, the switch — forms one LAN.

The defining traits of a LAN:

• Full ownership and control: the company buys the equipment, runs the cables and sets the rules. There is no carrier fee for internal traffic.
• High speed and low latency: with short distances and your own equipment, 1 Gbps per workstation is standard today (and 10 Gbps or more toward servers).
• Dominant technology: Ethernet over twisted pair cable, with switches as the central device (we met them in the previous lesson).

A WLAN (Wireless LAN) is exactly the same thing as a LAN, except the transmission medium is the air: the technology is Wi-Fi and the device that makes it possible is the access point. It is essential to understand that the WLAN is not a separate network from the LAN, but its wireless extension: in Valencia, a laptop connected over Wi-Fi and a PC cabled to the switch are on the same local network and share the server and printer as normal.

The usual professional criterion: cable for fixed workstations and everything critical (server, printer, desktop machines), Wi-Fi for mobility (laptops in meeting rooms, phones, visitors). That is exactly the split we will apply at Grupo Meridiano.

A MAN (Metropolitan Area Network) covers a city or a campus: bigger than a LAN, smaller than a WAN. Typical examples:

• The network interconnecting a university's buildings scattered across a city.
• A city council's fiber network linking its offices, libraries and sports centers.
• A local carrier's network serving one city.

In practice, the MAN is the least visible type for a small business: the company almost never builds it itself (laying fiber along public streets requires permits and carrier-scale budgets); instead, it is bought as a service. If Grupo Meridiano opened a second office in Valencia, in another neighborhood, and a carrier offered to link them with dedicated fiber within the city, that link would technically be traffic over a MAN.

A WAN (Wide Area Network) connects networks that are geographically far apart: between cities, countries or continents. Its traits are the mirror image of the LAN's:

• It isn't yours: the infrastructure (submarine fibers, national backbones, exchanges) belongs to carriers. You subscribe to the service.
• Recurring cost: a LAN is paid for once (equipment and cabling); a WAN is paid for every month.
• Lower speed and higher latency than a LAN: data travels hundreds or thousands of kilometers and crosses many intermediate devices.
• The border device between your LAN and the WAN is the router: that is why each site in Grupo Meridiano's inventory has one.

The WAN par excellence is the Internet: a worldwide network formed by the interconnection of millions of networks (hence its name: inter-networks). But beware: it is not the only WAN. A large corporation can lease private WAN links between its sites from a carrier, links that never touch the Internet. They are very reliable and very expensive; for a 25-person business like ours, the realistic option is a different one, and we will see it at the end of the lesson: using the Internet as transport with a VPN.

This diagram sums up Grupo Meridiano's real situation: two LANs (one per site) that can only talk to each other across a WAN (the Internet) they do not control.

Reach is not everything. Within the same LAN, machines can be organized in two very different ways depending on who provides the services.

In the client-server model the roles are separate: some dedicated machines (servers) provide services and the rest (clients) consume them. It is the model from the previous lesson: the Valencia file server provides, the 20 PCs request.

• Advantages: centralized administration (users, permissions, backups in one place), better security, scales well as you grow.
• Drawbacks: the server costs money and expertise, and it is a critical point: if it goes down, the service goes down for everyone.

In the peer-to-peer model ("among equals") there are no dedicated servers: every machine is both client and server at once. Each one shares whatever it wants (a folder, a printer) directly with the others.

• Advantages: zero additional cost, instant setup. For 3–5 home machines it may be enough.
• Drawbacks: no central administration. Permissions are configured machine by machine, nobody guarantees backups, and if the PC sharing the folder is switched off, there is no folder. Beyond a handful of machines it becomes unmanageable.

Important: this is a logical classification, not a physical one. The same LAN, with the same cables and the same switch, can operate either way; what changes is how the services are organized. Grupo Meridiano, with 25 employees and a file server, is clearly client-server: it is the right choice for any company that needs control and serious backups. Bilbao, with no server of its own, tolerates small P2P exchanges among its 5 machines for now, but the goal of this course will be for Bilbao to consume the services of the Valencia server.

The third classification: who may use the network.

• Private network: access is restricted to an organization or group. The Valencia and Bilbao LANs are private: only employees (and authorized devices) connect. A password on the Wi-Fi, or having to be physically inside the office to plug in a cable, are the barriers to entry.
• Public network: anyone may use it. The Internet is the supreme example, and so are the Wi-Fi of a coffee shop, a hotel or an airport.

The practical consequence is a security one, and it should be engraved in your memory right now:

Anything traveling over a public network can, in principle, be observed by third parties. Inside your private network you make the rules; on a public network you don't know who else is connected or who administers the intermediate equipment.

A direct example from our case: if a Grupo Meridiano consultant works from a hotel's public Wi-Fi, her data travels over a network nobody at the company controls. And there is a second, even more structural problem: the company's two sites need to exchange files daily, and the only path between Valencia and Bilbao is... the Internet, a public network. Do we send clients' internal documents across it in the clear? Obviously not. The solution has a name of its own.

A VPN (Virtual Private Network) creates an encrypted tunnel through a public network, so that two distant networks (or a user and a network) communicate as if they were connected by a private cable, even though their data actually crosses the Internet.

The idea, without getting into the technology yet (the protocols will arrive in module 2):

1. The Bilbao router and the Valencia router establish a tunnel between them: an agreed channel across the Internet.
2. Everything entering the tunnel travels encrypted: the Internet's intermediate devices see data go by, but cannot read it or know what it contains.
3. For employees, the result is transparent: someone in Bilbao opens the Valencia file server as if it were in the office next door.

Two variants worth telling apart from the start:

The VPN completes our vocabulary of types: joining Grupo Meridiano's two sites will be a virtual private network over a public WAN. For now the concept is enough; its actual configuration requires pieces (protocols, addressing) that we will build up in modules 2 and 5.

Let's apply the whole lesson to the inventory we made previously. Every element of the company now fits into a box:

And the full picture, which we will reuse throughout the course:

Note the dashed line: the VPN is not a new cable, it is a virtual tunnel traveling over the same Internet links that already exist.

• Treating the WLAN as "another network": the office Wi-Fi is not a different network from the wired one; it is the same LAN over a different transmission medium. A laptop on Wi-Fi and a cabled PC in Valencia see the same server and the same printer.
• Believing the Internet is "the company's WAN": the Internet is a public WAN the company uses, not one it owns. The difference matters: over what you don't own you have no guarantees of security or performance — which is exactly why VPNs and service contracts exist.
• Thinking P2P and client-server depend on the cabling: they are logical organizations of the services. You can move from one to the other without touching a single cable.
• Assuming a VPN "speeds up" the connection: a VPN provides privacy, not speed. In fact, encrypting and encapsulating adds a small overhead. Its value is being able to treat a public network as if it were private.
• Forgetting the PAN in corporate security: a company phone paired over Bluetooth with a rental car, or an improvised tethering session, are also networks and can also leak data. The company's perimeter does not end at the office door.
• Tip: whenever you analyze any network scenario, always ask the three questions from this lesson: what is its reach? how are the services organized? who can access it? With those three answers you already have half the picture.

State which network type by reach (PAN, LAN, WLAN, MAN or WAN) best describes each situation:

1. The 5 Bilbao machines cabled to their switch.
2. A consultant presents a report at a client's premises, projecting from her laptop, which is connected to her phone over Bluetooth to share data.
3. A city council links its 12 offices across the city with its own fiber.
4. The link through which the Valencia router sends traffic out to a server located in Germany.
5. The laptops in the Valencia meeting room connected to the access point.

Grupo Meridiano has just hired two interns in Bilbao. Since there is no server there, one employee suggests: "let each of us share our project folder with the others from our own PC, like the five of us do now". The IT lead in Valencia would rather have Bilbao access the Valencia file server through the future VPN. List two advantages and one drawback of each proposal and argue which one you would recommend.

A Grupo Meridiano consultant is working from a hotel in Seville this week and needs to download confidential documentation from the Valencia server. Answer:

1. What type of network is the hotel Wi-Fi under the private/public classification, and what risk does it carry?
2. Which VPN variant does she need: site-to-site or remote access? Why?
3. Once the VPN is up, why do we say she works "as if she were in the office" even though her data crosses half of Spain over the Internet?

Solution 1:

1. LAN: a wired local network in a single space under a single administration.
2. PAN: one person's devices within a few meters over Bluetooth.
3. MAN: it covers a city; bigger than a LAN, smaller than a WAN.
4. WAN: long-distance communication (Spain–Germany) over carrier infrastructure; in this case, the Internet.
5. WLAN: the wireless extension of the Valencia LAN through the access point.

Solution 2:

P2P proposal (shared folders among the Bilbao machines):

• Advantages: zero additional cost (nothing to buy or maintain) and immediate rollout.
• Drawback: scattered administration: permissions configured machine by machine, no guaranteed backups, and folders vanish when their owner shuts down the PC. With 7 people it starts becoming unmanageable.

Client-server proposal (accessing the Valencia server over VPN):

• Advantages: administration and backups centralized in a single point controlled by IT, and consistent permissions company-wide (Bilbao and Valencia see the same files).
• Drawback: dependency on the link: if either site's Internet connection (or the VPN) goes down, Bilbao loses access to the files.

Recommendation: client-server via VPN. Grupo Meridiano handles client documentation that demands access control and serious backups, and the Bilbao headcount is growing; P2P was only tolerable as a temporary workaround for 5 machines. The dependency drawback can be mitigated (for example, with a backup line), whereas P2P's lack of control cannot.

Solution 3:

1. It is a public network: anyone can connect, and the consultant doesn't know who else is on it or who administers its equipment. The risk is that third parties may observe or intercept her traffic.
2. Remote-access VPN: it connects an individual device (her laptop) to the company network. A site-to-site VPN joins two whole networks permanently (router to router), which is not this case.
3. Because the VPN tunnel encrypts all her traffic to the Valencia network: even though her data physically crosses the Internet, nobody along the way can read it, and logically her laptop behaves like one more machine on the company's private network. That is exactly what "virtual private network" means.

We can now put a first and last name on every network around us. By reach: PAN (one person's devices), LAN and its wireless extension WLAN (a building's network, like each Grupo Meridiano site), MAN (a city) and WAN (long distances, with the Internet as the supreme example). By service organization: client-server (our company's model, with its file server in Valencia) versus peer-to-peer (valid only for very small scenarios). By access: private networks, where we make the rules, versus public networks, where there are no guarantees. And we have conceptually solved Grupo Meridiano's big problem: joining Bilbao to Valencia with a site-to-site VPN, an encrypted tunnel that turns a public network into an extension of the private one. But knowing what type of network we have still doesn't tell us how to connect the machines to one another inside each one: everything onto one shared cable? everything to a central point? each machine to every other? The way devices are interconnected has a name — topology — and direct consequences for cost, performance and what happens when something fails. That is the subject of the next lesson, Network Topologies, where we will design the network of Grupo Meridiano's two sites on paper.