Computer Networks · TEE · papers
Q1(c) · Classful IPv4
2025-12-05 · 2022-23
Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.
Q1(c). Explain the classes of IP address. [5 marks]
Answer
An IPv4 address identifies an IP interface. The network prefix selects the destination network; remaining bits identify an address within it. Classful addressing is historical; modern routing uses explicit CIDR prefixes.
| Class | First octet | Default mask | Network / host split | Purpose |
|---|---|---|---|---|
| A | 1–126 (ordinary unicast) | 255.0.0.0 (/8) | 8 / 24 bits | Large historical unicast networks; 0 and 127 reserved |
| B | 128–191 | 255.255.0.0 (/16) | 16 / 16 bits | Medium historical unicast networks |
| C | 192–223 | 255.255.255.0 (/24) | 24 / 8 bits | Small historical unicast networks |
| D | 224–239 | No unicast default mask | Not network/host class split | Multicast |
| E | 240–255 | No unicast default mask | Not normal unicast allocation | Reserved/experimental; special addresses exist |
Example: 114.34.2.8 is class A with network 114.0.0.0 and host portion 34.2.8. Class does not override an explicitly supplied CIDR prefix.