Networking & Internet

1PAN, LAN, MAN and WAN by area

Networks are sorted by the area they cover. In increasing size the order is PAN < LAN < MAN < WAN. A LAN covers a building or campus; a MAN covers a city; a WAN spans countries. The Internet is the largest WAN in the usual exam phrasing.

Order by area covered — Personal, Local, Metropolitan, Wide — not by which one is "faster".

Figure. Area grows outward: PAN inside LAN inside MAN inside WAN.

2Network topologies

Topology names how nodes are linked. Bus uses a single backbone. Star uses a central switch or hub. Ring forms a loop. Mesh interconnects nodes richly (every node interconnected in the full-mesh exam picture). Tree is hierarchical.

Star is easiest to troubleshoot because faults often localise at the centre; mesh is most fault-tolerant but costliest.

Figure. Star links every node to a centre; bus hangs nodes on one shared backbone.

3Hub, switch and router by layer

Three devices are paired with layers and jobs. A hub broadcasts to all ports and is treated as Layer 1 (physical). A switch forwards by MAC address at Layer 2. A router connects different networks by IP address at Layer 3.

Router = routes between networks (IP); switch = within one network (MAC). A hub or switch alone does not replace a router when two different IP networks must exchange packets.

Figure. Hub floods at Layer 1; switch filters on MAC at Layer 2; router forwards on IP at Layer 3.

4Key application protocols

Protocol questions match a job to a name. HTTP and HTTPS carry the web; FTP transfers files; SMTP sends mail; POP3 and IMAP receive mail. TCP/IP is the core suite underneath everyday Internet communication.

SMTP = Sending Mail (both start with S); POP/IMAP retrieve. HTTPS is HTTP plus SSL/TLS security — the padlock cue means the connection is encrypted.

Figure. Match each protocol to its job: web, file transfer, outbound mail, name lookup.

5Default ports

Default port numbers are paired with protocols in static GK: HTTP = 80, HTTPS = 443, FTP = 21, SMTP = 25, DNS = 53. Questions usually ask the number for a named service, or the service for a named number.

Do not invent ports outside this sourced list for this topic.

Figure. Default ports are fixed exam facts: HTTP 80, HTTPS 443, FTP 21, SMTP 25, DNS 53.

6IPv4 and IPv6 address sizes

An IPv4 address is 32 bits, written as four octets (each 0–255), for example 192.168.1.1. An IPv6 address is 128 bits. Bit width is the fact papers test — not a weekly "current adoption rate".

Four octets × 8 bits = 32 bits is the structure of the IPv4 notation, not a pacing-style multi-step method problem.

Figure. Address width is the cut: IPv4 is 32 bits; IPv6 is 128 bits.

7WWW, URL and DNS

The World Wide Web (WWW) is a service — collections of web pages accessed through browsers — not a synonym for the entire Internet. A URL locates a resource. DNS maps human-readable domain names to IP addresses so browsers can find hosts.

When a stem says a name must become a number before a page loads, it is describing DNS resolution.

Figure. A URL names a resource; DNS resolves the host name to an IP; then the browser fetches the page.

Name to address

1. User enters a URLThe browser needs the host's IP address, not only the domain string.
2. DNS lookupDNS resolves the domain name to an IP address (default port 53).
3. Fetch the resourceThe client contacts that IP using web protocols (HTTP/HTTPS) to load the page.

8Bandwidth in bits per second

Bandwidth is measured in bits per second (bps). The notes fix the mega scale as 1\ \mathrm{Mbps} = 10^{6} bits/second. Questions that name Mbps are asking for that power-of-ten meaning, not for a live ISP plan price.

Keep bits per second distinct from bytes in storage questions — networking bandwidth here is in bits.

Figure. Bandwidth is bits per second. Kbps, Mbps and Gbps are thousand-fold steps.