IP Addressing, Protocols and Ports
IPv4 and IPv6
| IPv4 | IPv6 | |
|---|---|---|
| Size | 32 bits | 128 bits |
| Format | Four numbers 0 to 255 separated by dots: 192.168.1.10 | Eight groups of hexadecimal: 2001:0db8:85a3::8a2e:0370:7334 |
| Addresses | About 4.3 billion | Practically unlimited |
An IP address is the logical address of a device on a network. A MAC address is the physical 48-bit address burned into the NIC, written in hexadecimal (for example 00:1A:2B:3C:4D:5E).
IPv4 classes
| Class | First number range | Default mask | Use |
|---|---|---|---|
| A | 1 to 126 | 255.0.0.0 | Very large networks |
| B | 128 to 191 | 255.255.0.0 | Medium networks |
| C | 192 to 223 | 255.255.255.0 | Small networks |
| D | 224 to 239 | None | Multicasting |
| E | 240 to 255 | None | Experimental |
127.x.x.x is reserved for loopback (127.0.0.1 = "localhost", your own computer). Private ranges (not routable on the Internet): 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, 192.168.0.0 to 192.168.255.255.
Worked examples. 172.20.5.9 starts with 172, so it is Class B. A /24 network (mask 255.255.255.0) has 2^8 = 256 addresses, of which 254 can be used for hosts (one is the network address, one the broadcast).
Key network protocols
| Protocol | Full form and use | Port |
|---|---|---|
| HTTP | HyperText Transfer Protocol: web pages | 80 |
| HTTPS | HTTP Secure (SSL/TLS encryption) | 443 |
| FTP | File Transfer Protocol | 21 (control), 20 (data) |
| SSH | Secure Shell: safe remote login | 22 |
| Telnet | Remote login, not secure | 23 |
| SMTP | Simple Mail Transfer Protocol: sends email | 25 |
| DNS | Domain Name System: name to IP address | 53 |
| DHCP | Dynamic Host Configuration Protocol: gives IP addresses automatically | 67 and 68 |
| POP3 | Post Office Protocol: downloads email | 110 |
| IMAP | Internet Message Access Protocol: reads email on the server, synced across devices | 143 |
| SNMP | Network management | 161 |
| RDP | Remote Desktop Protocol | 3389 |
| ICMP | Used by ping to test reachability | none |
Other terms: NAT lets many private devices share one public IP. ARP finds a MAC address from an IP address. ping tests a connection; ipconfig (Windows) and ifconfig or ip a (Linux) show the IP settings; tracert shows the route of packets.
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from standard computer textbooks, Microsoft documentation and official sources. Features differ between Excel and Word versions (2016, 2019, 2021, 365) so check which version your exam follows. Found a mistake? Tell us.