# Q6(d) · Classful and IPv6 addresses

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2024-feb-ai-reexam/q6d

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2024-feb-ai-reexam--q6d/

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

### Q6(d). I. Find the class of (i)11000011 00111011 00001011 11101111 and (ii)129.5.25.111. II. Distinguish IPv4 and IPv6 addresses. [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.

### Step 1. Classify the first octets

11000011₂=128+64+2+1=195: ClassC. 129 lies in128–191: ClassB.

**Definition.** IPv6 extends address size and reorganizes IP forwarding information into a fixed base header with extension headers.

**Simple meaning.** Sirf address bada nahi; header ka arrangement bhi badla.

## Understand it step by step

1. IPv6 uses unicast, multicast and anycast addressing; it does not use IPv4-style broadcast addressing.
2. Unicast identifies an interface; multicast addresses a group; anycast reaches one appropriate member of a group sharing an address, according to routing.
3. ::1 is loopback. fe80::/10 is link-local space. ff00::/8 identifies multicast. These serve different purposes.
4. IPv6 neighbour discovery replaces IPv4 ARP mechanisms. Do not write that IPv6 uses ARP to map its addresses.
5. IPv6 is not automatically encrypted or secure merely because it has a larger address space. Security depends on the mechanisms deployed.

| Feature | IPv4 | IPv6 |
| --- | --- | --- |
| Address width | 32 bits | 128 bits |
| Base/header size | 20–60 bytes depending on options | 40-byte fixed base header |
| Length field | Total length includes IPv4 header | Payload Length excludes 40-byte base header |
| Lifetime field | TTL | Hop Limit |
| Following protocol | Protocol field | Next Header; may identify an extension |
| Header checksum | Present | No base-header checksum |
| Options | Inside IPv4 header | Typically extension headers |
| Fragmentation fields | In IPv4 header; routers may fragment if permitted | Fragment extension header; fragmentation by source, not routers |

#### Practical example

A router handling an oversized IPv6 packet cannot fragment it on behalf of the source; the source must respond to path-MTU information and use an appropriate packet size or source fragmentation.

**Yaad rakho:** v4 total length; v6 payload length.