Summary

This lesson introduces several key networking concepts.

It starts with networking hardware, especially routers, switches, and NICS.

Routers are actually little computers and can be configured to control your access to the internet and your local network security. This extends to assigning IP addresses, opening or closing ports, and for some routers, providing Domain Name Lookup Services (or at least handling connections to real DNS servers).
Switches are much simpler than routers. They essentially allow you to plug in lots of ethernet cables. Companies do sometimes produce hybrid devices that include both router and switch capabilities.
NICS: Routers and switches are separate devices that sit outside your computer, but your computer must also have a way to connect to the network. This is accomplished by a NIC (network interface card). The NIC might be built into your computer motherboard, or you might actually buy one and install it. It has an identifying number called a MAC address. This is like a serial number.

Many networking concepts don't correspond to tangible hardware. Instead, they are more conceptual. This includes ideas like IP addresses, URLs, and ports.

MAC Address=>IP Address When your computer gets an IP address (which is like a phone number allowing it to connect to the internet), that IP address is associated with the NIC ID (a.k.a MAC address or hardware address). Your IP address can change, but the hardware address is constant.
IP Address=>URL A company that provides a service on the network (like a website) typically uses a name (like google.com) instead of an IP address. The name is more accessible for us humans. A service called DNS (Domain Name Service) provides a lookup table so that any name (URL) you type into your browser window can be resolved to the correct IP address and routed to that connection.
Ports You can't connect to a machine's IP address. You have to connect to a service provided by that machine. Each service corresponds to a particular port. The service (a.k.a daemon) listens for attempted connections to its port and then allows the connection based on a set of rules. If a service is promiscuous, it may not be very cautious about who can connect, making it vulnerable to hackers.

Why not use the MAC address instead of the IP address?

A company like Google replaces computers all the time. So, it is much more reasonable to maintain a consistent IP address and just replace the hardware behind the scenes.

In sum, a network requires appropriate hardware, and a system of addresses, rules, and services that help keep the whole arrangement organized.

Analogies

IP Address ≈ phone number
hosts table ≈ address book
DNS ≈ information (411)
URL ≈ name
Server ≈ service
Port ≈ extension number
Hardware: NIC (network interface card) ≈ SIM card
MAC address ≈ SIM card ID (IMSI)

Networking 1 (10)