Networking Fundamentals: Hands-on Training for Beginners

A hash function turns input of any size into a fixed-size fingerprint in a way that cannot be reversed, so that the fingerprint can verify data or store a password without holding the original.

A public key infrastructure is the system of certificates, certificate authorities and revocation mechanisms that lets a party verify which identity a public key belongs to before trusting it.

Authentication is the process of confirming that a user, device or service is who it claims to be, typically by checking something it knows, has or is.

IP addressing is the scheme that gives every interface on a network a numeric address, with IPv4's four-byte addresses now supplemented by IPv6's much larger space, and with private ranges reserved for use inside networks that reach the internet through translation.

Subnetting divides an address block into smaller networks by choosing how many leading bits identify the network, written as a prefix length or a subnet mask, so that each subnet has its own range of host addresses and its own routing entry.

Routing is how packets move between networks: each router holds a table of known destinations and the next hop toward each, learned by configuration or by a protocol, and forwards each packet to the most specific match.

Uptime is the proportion of time a service answers requests, quoted in nines, and a service level agreement is the contract clause setting out how that proportion is counted and what the provider owes when it falls short.

Shared hosting puts your website on a machine that is simultaneously running hundreds of other people's, pooling its processor, memory and disk between all of you, which is both why it costs so little and why your speed partly depends on strangers.

A VPS is a software-defined slice of one physical machine that behaves as a server in its own right, with its own operating system, reserved CPU, memory and disk, and administrative access down to the kernel.