Networking: Devices, Topologies & Protocols
🔒 Log in to trackProtocols and port numbers; TCP vs UDP
🔒 Log in to track| Protocol | Port | Purpose |
|---|---|---|
| HTTP | 80 | Web pages (plain) |
| HTTPS | 443 | Web over TLS/SSL encryption |
| FTP | 21 (control) / 20 (data) | File transfer |
| SSH | 22 | Secure remote login (encrypted successor of Telnet) |
| Telnet | 23 | Plain-text remote login (insecure) |
| SMTP | 25 | Sending e-mail |
| DNS | 53 | Name-to-IP resolution |
| DHCP | 67/68 | Automatic IP assignment |
| POP3 | 110 | Receive e-mail (download) |
| IMAP | 143 | Receive e-mail (sync) |
| SNMP | 161 | Network management/monitoring |
| RDP | 3389 | Windows remote desktop |
TCP (Transmission Control Protocol) - connection-oriented, 3-way handshake (SYN, SYN-ACK, ACK), guaranteed ordered delivery: web, e-mail, file transfer. UDP (User Datagram Protocol) - connectionless, no delivery guarantee, faster/lower overhead: DNS queries, DHCP, video/audio streaming, VoIP, online gaming. Standards: Ethernet = IEEE 802.3, Wi-Fi = 802.11, Bluetooth = 802.15.
Detailed notes
Ports — numbered doors on a machine
While the IP address finds the computer, the port number finds the service (door) on it. The classic exam set:
| Protocol | Port | Job |
|---|---|---|
| HTTP | 80 | web pages (plain) |
| HTTPS | 443 | web pages encrypted (TLS/SSL) |
| FTP | 21 (control; 20 = data) | file transfer |
| SSH | 22 | secure remote login |
| Telnet | 23 | remote login (NOT encrypted) |
| SMTP | 25 | sending e-mail |
| DNS | 53 | name to IP resolution |
| POP3 | 110 | receiving e-mail (download) |
| IMAP | 143 | receiving e-mail (sync) |
Anchor pairs: 80/443 web, 21/23/25 climbing odd numbers (FTP, Telnet, SMTP), 53 DNS, 110/143 mail-in.
TCP vs UDP — the two delivery styles
| TCP (Transmission Control Protocol) | UDP (User Datagram Protocol) | |
|---|---|---|
| Connection | connection-oriented (handshake first) | connectionless (just send) |
| Reliability | guaranteed, ordered, error-checked | no guarantee — fast but unsafe |
| Speed | slower | faster |
| Used by | web (HTTP/HTTPS), e-mail (SMTP), file transfer (FTP) | live streaming, gaming, VoIP, DNS queries, DHCP |
Memory hook: TCP = Tracked, Careful, Precise; UDP = Untracked, Dashes. Live cricket streaming chooses UDP — one lost frame is better than a paused match.
The protocols behind one web visit
- DNS (UDP 53) turns the name into an IP.
- TCP opens the connection.
- HTTPS (TCP 443) requests and delivers the page encrypted. For e-mail: SMTP sends, POP3/IMAP receive — over TCP.
Full forms worth memorising
HTTP HyperText Transfer Protocol; HTTPS secure HTTP over TLS/SSL; FTP File Transfer Protocol; SMTP Simple Mail Transfer Protocol; POP Post Office Protocol; IMAP Internet Message Access Protocol; TCP Transmission Control Protocol; UDP User Datagram Protocol; DNS Domain Name System; DHCP Dynamic Host Configuration Protocol; SSH Secure Shell.
Reading a protocol question in the exam
Ask first: is the question about a direction (send mail = SMTP, receive = POP3/IMAP), a number (port), a style (reliable or fast), or a full form? For port questions, if you cannot recall the exact number, eliminate by neighbourhood — 21-22-23 are the file/remote trio, 25 is the mail sender, 80/443 the web pair, 110/143 the mail-in pair. For TCP-or-UDP questions, ask what a lost packet would cost: a corrupted file (use TCP) or one blurred frame (UDP is fine).
Quick revision
- HTTP 80, HTTPS 443, FTP 21, SSH 22, Telnet 23, SMTP 25, DNS 53, POP3 110, IMAP 143.
- TCP = reliable, connection-oriented (web, mail, FTP); UDP = fast, connectionless (streaming, games, VoIP).
- Telnet is plaintext; SSH (22) is its encrypted replacement.
- HTTPS = HTTP + TLS/SSL encryption.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: Port-number matchingvery common4 practice Q
'HTTPS works on which port', 'port of SMTP/FTP/DNS/POP3', or a matched pair with one number shifted.
- Anchors: HTTP 80, HTTPS 443, FTP 21, SSH 22, Telnet 23, SMTP 25, DNS 53, POP3 110, IMAP 143.
- The classic trap: 443 for plain HTTP or 80 for HTTPS.
- Remember 21-22-23 climbing (FTP, SSH, Telnet) and 25 as the mail sender's door.
Example: HTTPS uses which port number by default?
443 — plain HTTP uses 80; the S (secure) doubles the number in exam memory: 80 becomes 443.
Type 2: TCP vs UDP selectionvery common4 practice Q
'Which protocol is used for live streaming / file transfer', 'which is connection-oriented', reliability-vs-speed statements.
- TCP: connection-oriented, reliable, ordered — web, e-mail, FTP.
- UDP: connectionless, fast, no delivery guarantee — live streaming, gaming, VoIP, DNS queries.
- The classic exam answer: live video streaming = UDP; downloading a file = TCP.
Example: Which transport protocol suits a live cricket stream?
UDP — speed matters more than perfect delivery; TCP's retransmissions would only pause the match.
Type 3: Protocol purpose identificationcommon3 practice Q
'Which protocol transfers files', 'which protocol sends e-mail', 'which service resolves names' — purpose matching across the famous protocols.
- File transfer = FTP; send mail = SMTP; receive mail = POP3/IMAP; web pages = HTTP/HTTPS; names = DNS; remote login = Telnet (plain) / SSH (secure).
- FTP has two ports: 21 control, 20 data.
- DHCP assigns IP addresses automatically.
Example: Which protocol is used to transfer files between computers?
FTP (File Transfer Protocol) — control on port 21, data on port 20.
Type 4: Protocol full forms and securitycommon3 practice Q
'Full form of FTP/TCP/UDP/DHCP', 'which remote-login protocol is secure', or Telnet-vs-SSH statements.
- FTP = File Transfer Protocol; TCP = Transmission Control Protocol; UDP = User Datagram Protocol; DHCP = Dynamic Host Configuration Protocol; SSH = Secure Shell.
- Telnet (23) sends everything in plaintext; SSH (22) is the encrypted replacement.
- HTTPS = HTTP over TLS/SSL.
Example: Which protocol provides an ENCRYPTED remote login?
SSH (Secure Shell), port 22 — Telnet on port 23 sends passwords as plain text.
Shortcut tricks
⚡ Port anchors
Memorise six: 80 HTTP, 443 HTTPS, 25 SMTP, 53 DNS, 110 POP3, 21 FTP - these cover most CKT options. Then '22 SSH, 23 Telnet' (Telnet = the insecure 23).
Example: Default port of HTTPS?
⚡ TCP = Tracked, UDP = Untracked
TCP Tracks every packet (reliable, slower - web/mail/files); UDP is Unreliable but quick (streaming, gaming, DNS). 'Guaranteed delivery' in the question = TCP.
Example: Live cricket video streaming mainly uses?
UDP (speed over retransmission).
Where students lose marks
Giving HTTP the 443 port - 443 is HTTPS; plain HTTP is 80.
Choosing TCP for live streaming in the classic question - the intended answer is UDP (speed first).
Saying Telnet is secure - SSH (22) is the encrypted one; Telnet (23) sends everything in clear text.
Practice sets — 17 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 10 questions
Suggested time 5 min · wrong answers go to your mistake notebook automatically.