# Q6(a) · Classful network and host portions

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2024-ai-final/q6a

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2024-ai-final--q6a/

Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.

### Q6(a). Identify class, default subnet mask, network, broadcast and host portion for (a)191.5.8.9 and (b)214.25.6.3. [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.

### Given

191.5.8.9 and214.25.6.3; historical default class masks.

### To find

Class, mask, network, broadcast and host portion.

### Formula and why

Network = address AND mask; broadcast = network with all host bits1.

Without a custom prefix the question’s classful default determines the split.

### Solution

| Address | Class | Mask | Network | Broadcast | Host portion |
| --- | --- | --- | --- | --- | --- |
| 191.5.8.9 | B | 255.255.0.0 (/16) | 191.5.0.0 | 191.5.255.255 | 8.9 (16 bits) |
| 214.25.6.3 | C | 255.255.255.0 (/24) | 214.25.6.0 | 214.25.6.255 | 3 (8 bits) |

The supplied address itself is a host address; “host portion” means the suffix left after removing the network bits.