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Client Server Model

A client is a thing that talks to servers. A server is a thing that talks to clients. The client—server model is a thing made up of a bunch of clients and servers talking to one another.

Client​

  1. A machine or process that requests data from a server.
  2. Note that a single machine or piece of software can be both a client and a server at the same time. For instance, a single machine could act as a server for end user and as a client for a database.

Server​

  1. A machine or process that provides data or service for a client, usually by listening for incoming network calls.
  2. Note that a single machine or piece of software can be both a client and a server at the same time. For instance, a single machine could act as a server for end users and as a client for a database.

Client Server Model​

  1. The paradigm by which modern systems are designed, which consists of clients requesting data or service from servers and servers providing data or service to clients.

IP Address​

An address given to each machine connected to the public internet. IPv4 addresses consist of four numbers separated by dots: a.b.c.d where all four numbers are between 0 and 255. Special values include:

  1. 127.0.0.1 : Your own local machine. Also referred to as localhost
  2. 192.168.x.y: Your private network. For instance, your machine and all machines on your private wifi network will usually have the

Port​

In order for multiple programs to listen for new network connections on the same machine without colliding, they pick a port to listen on. A port is an integer between 0 and 65,535 (2^16 ports total).

Typically, ports 0-1023 are reserved for system ports (also called well-known ports) and shouldn't be used by user-level processes. Certain ports have pre-defined uses, and although you usually won't be required to have them memorized, they can sometimes come in handy. Below are some examples:

  1. 22: Secure Shell
  2. 53: DNS lookup
  3. 80: HTTP
  4. 443: HTTPS

DNS​

Short for Domain Name System, it describes the entities and protocols involved in the translation from domain names to IP Addresses. Typically, machines make a DNS query to a well known entity which is responsible for returning the IP address (or multiple ones) of the requested domain name in the response.