Network Layer ll

Question 1

Key fields in an IPv4 header

Answer 1

• Version (4-bit): IPv4/6
• Header Length: Typically 20 bytes (no options)
• TTL (8-bit): Prevents infinite loops; decremented by routers
• Protocol (8-bit): Identifies transport layer protocol
• Source/Dest IP (32-bit): Logical addresses
• Fragmentation Fields (ID, Flags, Offset): For packet splitting/reassembly

Question 2

How is the header checksum used?

Answer 2

Detects bit errors in the header; recomputed at each router

Question 3

Why does IPv4 fragment datagrams?

Answer 3

Links have different MTUs. Fragments share the same ID but have unique offsets

Question 4

How is the offset calculated?

Answer 4

Offset = (Previous Fragment’s Data Length) / 8

Question 5

What is CIDR notation?

Answer 5

/24 means the first 24 bits are the network prefix; remaining 8 bits (/32) for hosts

Question 6

How are interfaces addressed?

Answer 6

Each interface has a unique IP. Subnets group interfaces

Question 7

What are private IP ranges?

Answer 7

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16 (non-routable on public internet)

Question 8

Why was IPv6 introduced?

Answer 8

IPv4 address exhaustion. IPv6 uses 128-bit addresses (vs 32-bit)

Question 9

Key IPv6 improvements

Answer 9

• Fixed 40-byte header: Faster processing (no checksum, optional fields)
• Is smarter with new address types: Unicast, multicast, anycast (deliver to nearest in group)
• No fragmentation: Handled by endpoints, not routers

Question 10

IPv4 vs IPv6

Answer 10

Address Size- IPv4: 32-bit, IPv6: 128-bit
Header- IPv4: Variable 20+ bytes, IPv6: Fixed 40 bytes
Fragmentation- IPv4: Routers fragment, IPv6: Senders only
Checksum- IPv4: Header checksum, IPv6: No checksum (rely on upper layers)