LAN components and functions

Early LANs were mostly PCs, file servers, print servers, hubs, and bridges. Hubs and bridges are dead, replaced by switches. A typical small office today: routers, switches, APs, servers, IP phones, mobile phones, PCs, laptops.

The four fundamental components

Every LAN, whatever its size, needs these four things.

1. Hosts

Any device that can send or receive data on the LAN. Also called endpoints; the terms are interchangeable.

2. Interconnections

How data physically gets from point to point:

• NICs: translate device data into frames that can go on the wire. Connect over copper, fiber, or wireless.
• Network media: traditionally copper and fiber cables; modern LANs (even home ones) almost always include a WLAN.

3. Network devices

They deliver data between hosts:

• Ethernet switch (L2): the aggregation point of the LAN, intelligent frame distribution.
• Router, aka gateway (L3): connects LAN segments to each other and to the internet.
• AP (L2): wireless connectivity into the LAN.

4. Protocols

The rules governing transmission. Common LAN protocols:

• Ethernet (IEEE 802.2, 802.3)
• IP, TCP, UDP
• ARP (IPv4) / NDP (IPv6)
• CIFS (file sharing)
• DHCP

What a LAN is for

• Data and applications: share files and software, easier collaboration.
• Resources: shared input devices (cameras) and output devices (printers).
• A path to other networks: when a resource isn’t local, the LAN reaches it through a gateway (the internet being the big one).