Computer Networks and Internet Concepts
Scope
Computer Networks and Internet Concepts covers network types and topologies, devices, addressing, protocols and Internet services. Questions test which device or protocol fits a scenario and how a URL is resolved.
Core rules
- LAN is local, MAN metropolitan, WAN wide-area. Star topology uses a central switch/hub; bus shares a backbone; ring passes data around a loop.
- Hub repeats to all ports; switch forwards by MAC address; router forwards between networks by IP address.
- IP identifies a host/interface; MAC identifies a network card. DNS maps domain names to IP addresses.
- HTTP/HTTPS transfer web pages; HTTPS adds encryption and normally uses port 443. FTP transfers files. SMTP sends mail; POP3/IMAP retrieve mail.
- A URL has a protocol, host/domain, optional port, path and file.
Worked example
Take https://www.example.com/result/cs.html. Protocol: HTTPS. Host: www.example.com. Path: /result/. File: cs.html. The browser asks DNS for the host's IP address, opens a TCP connection to port 443, sends an HTTPS request for the path, and receives the HTML response. The domain name is not the server's physical address; DNS resolves it.
Traps
Do not say a switch routes between different networks; that is a router's job. SMTP is for sending, not for retrieving mail. HTTP is stateless, so it does not remember previous requests by itself. An IP address and a MAC address are not interchangeable.