DNS, DHCP, SSH, Proxy, HTTP, Email, FTP, and IRC Explained

Posted on Feb 19, 2025 in Contemporary Music Composition

Understanding Key Internet Protocols

DNS (Domain Name System) translates domain names to IP addresses, locating websites. Examples of domain extensions include:

  • .com – Commercial
  • .org – Organization
  • .edu – Educational
  • .net – Internet and communications
  • .gov – Governmental organizations

Domain delegation decentralizes DNS database administration. Reverse resolution returns a hostname given an IP address.

DHCP (Dynamic Host Configuration Protocol)

DHCP offers fast network configuration to clients. Allocation can be manual (static) or dynamic (automatic). When a computer starts without an assigned IP address, it requests a free IP from the DHCP server.

SSH (Secure Shell)

SSH is a secure communication protocol for remote machine login, providing authentication, confidentiality, and integrity. It supports any protocol relying on TCP/IP. OpenSSH is a well-known free version.

Symmetric vs. Asymmetric Keys

  • Symmetric Key: The same key is shared by sender and receiver for encryption and decryption (e.g., DES & IDEA).
  • Asymmetric Key: Uses a public and a private key. The public key encrypts, and the private key decrypts (e.g., RSA & DSA). Each user has a private key known only to them and a public key known to others.

An SSH tunnel is a communication tunnel between two computers for data transmission.

Proxy Servers

A Proxy server centralizes Internet traffic for a local network. A Transparent proxy uses NAT, making users unaware of the proxy.

HTTP (Hypertext Transfer Protocol)

HTTP is the most common method for exchanging data on the WWW, created in 1990 at CERN. There are request and response messages. SSL (Secured Sockets Layer) is a widely used encryption protocol designed by Netscape.

An electronic signature is a code created from a message to ensure authentication and integrity.

Email

Email is based on creating and transmitting messages between network users asynchronously. MIME specifications allow transparent exchange of all file types.

Email Components

  • MTA (Mail Transfer Agent): Transfers email messages between machines using SMTP.
  • MDA (Mail Delivery Agent): Copies messages from the mail server to the user’s mailbox.
  • MUA (Mail User Agent): The program users use to read and send messages (e.g., Outlook, Thunderbird).

Email Protocols

  • SMTP (Simple Mail Transfer Protocol): Transports outgoing mail from sender to recipient’s server, using port 25.
  • IMAP (Internet Message Access Protocol): Allows email clients to access messages stored on remote servers.
  • POP (Post Office Protocol): Manages, accesses, and transfers email messages between the remote server and the client machine.

FTP (File Transfer Protocol)

FTP is a standard procedure for transferring files between systems, using a client/server architecture.

FTP Modes

  • Active Mode: The client makes the first connection with a transfer request, and the server controls processes.
  • Passive Mode: Both connections are initiated by the client, preventing the control connection from being treated as foreign by routers or firewalls.

IRC (Internet Relay Chat)

IRC enables real-time communication between users on different operating systems. The process is:

  1. The user connects to an IRC server through an IRC client.
  2. Once connected, the user joins channels and identifies with a nickname (alias).