6. Network Layer (1)

Question 1

Which of the following is not a main service provided by the network layer?

A) Routing
B) Addressing
C) Error detection and correction
D) Packetizing

Answer 1

Answer: C) Error detection and correction

The network layer is responsible for routing, addressing, and packetizing. Error detection and correction are primarily handled at the data link and transport layers.

Question 2

The Internet is an example of an internetwork composed of interconnected LANs and WANs (True or false?)

Answer 2

True

The Internet connects many LANs and WANs through routers, forming an internetwork.

Question 3

What is the main role of a router in the Internet?

Answer 3

To deliver messages from one host to another by routing packets across interconnected networks.

Routers interconnect different networks (LANs/WANs), forwarding packets based on network-layer addressing.

Question 4

In connectionless packet switching, which of the following is true?
A) A virtual circuit is established before sending data
B) All packets follow the same path
C) Packets are routed independently
D) Packets must arrive in order

Answer 4

C) Packets are routed independently

In connectionless packet switching (datagram model), each packet is routed independently; there is no pre-established path.

Question 5

In connection-oriented packet switching, a virtual circuit is established before data transmission. (True or false?)

Answer 5

True

Connection-oriented services set up a path (virtual circuit) before sending packets, and all packets follow this path.

Question 6

What is the key difference between routing and forwarding in a router?

Answer 6

Routing involves determining the best path for packets using routing protocols; forwarding is the actual moving of packets based on the routing table.

Routing is about building and updating decision tables; forwarding uses those tables to direct packets.

Question 7

The switching fabric in a router affects the size of queues and overall packet delay. (True or false?)

Answer 7

True

The switching fabric’s performance influences how fast packets move between ports, impacting queue length and delay.

Question 8

Which component in a router performs the lookup and update of the routing table?
A) Input port
B) Output port
C) Routing processor
D) Switching fabric

Answer 8

C) Routing processor

The routing processor handles routing table operations. Input/output ports handle physical/datalink functions, and the switching fabric moves packets inside the router.

Question 9

Which of the following statements about MAC addresses is correct?
A) MAC addresses are used by routers for Internet routing
B) MAC addresses contain a network ID and host ID structure
C) MAC addresses are hardwired to NICs
D) MAC addresses are logical addresses

Answer 9

C) MAC addresses are hardwired to NICs

MAC addresses are assigned at the hardware (NIC) level. Routers use logical (IP) addresses, not MAC addresses, for Internet routing.

Question 10

An IPv4 address uniquely identifies a host on the Internet.

Answer 10

False

An IPv4 address uniquely identifies a connection of a device to the Internet, not the device itself. If a device moves, its IP address may change.

Question 11

What is the difference between binary and dotted-decimal notation for IPv4 addresses?

Answer 11

Binary notation writes all 32 bits separated into 8-bit groups; dotted-decimal uses decimal numbers for each octet, separated by dots.

Binary is clear for computers; dotted-decimal is compact and readable for humans.

Question 12

What is the primary reason classful addressing was replaced by classless addressing?
A) To simplify routing
B) To improve security
C) To prevent address wastage and depletion
D) To increase transmission speed

Answer 12

C) To prevent address wastage and depletion

Classful addressing wasted many addresses, especially in large (Class A) and small networks. Classless addressing (CIDR) allows variable-length prefixes, making allocation more efficient.

Question 13

Subnets allow an organization to divide an IP block into smaller ranges for internal use.

Answer 13

True

Subnetting splits a larger IP range into multiple smaller, logical subnetworks.

Question 14

What is the function of a netmask in IP addressing?

Answer 14

It separates the network ID from the host ID in an IP address by specifying which bits belong to each part.

A netmask uses 1s for network ID bits and 0s for host ID bits; logical ANDing an IP with its netmask reveals the network address.

Question 15

What does a router do if a destination IP address is not found in its routing table?
A) Drops the packet
B) Forwards the packet using the default route
C) Sends it to the output port with the lowest index
D) Broadcasts it to all interfaces

Answer 15

B) Forwards the packet using the default route

If there is no exact match in the routing table, the router uses the default route, if configured, to forward the packet.

Question 16

A default route is always required in every routing table.

Answer 16

False

The default route is optional but often included to handle packets with unknown destinations.

Question 17

Describe how a router uses a netmask during the forwarding process.

Answer 17

The router ANDs the destination IP with each netmask in its table and compares the result to the network address; if matched, it forwards the packet on the corresponding interface.

This process helps the router decide which network the packet belongs to for proper forwarding.

Question 18

Which field in the IPv4 header is not directly involved in fragmentation?
A) Identification
B) Flags
C) Fragmentation offset
D) Protocol

Answer 18

D) Protocol

Identification, Flags, and Fragmentation offset fields handle fragmentation. Protocol indicates the next layer protocol (e.g., TCP or UDP).

Question 19

IPv4 provides reliable, connection-oriented delivery of packets. (true or false?)

Answer 19

False

IPv4 is unreliable and connectionless; reliability must be provided by higher layers like TCP.

Question 20

What happens if an IPv4 packet is larger than the MTU of the network?

Answer 20

It is fragmented into smaller packets, each with its own header, and reassembled at the destination.

Fragmentation fields in the header manage this process.

Question 21

Which organization is responsible for allocating global IP address blocks?
A) IETF
B) ISO
C) ICANN
D) IEEE

Answer 21

: Which organization is responsible for allocating global IP address blocks?
A) IETF
B) ISO
C) ICANN
D) IEEE

ICANN assigns large IP address blocks to ISPs and organizations; IETF develops protocols, ISO standardizes models, IEEE handles MAC addresses.

Question 22

In CIDR notation, 192.168.1.0/24 specifies a block of 256 addresses.

Answer 22

True

/24 means the first 24 bits are network prefix, leaving 8 bits for hosts, resulting in 256 addresses.

Question 23

What are “supernets” in IP addressing?

Answer 23

Supernets aggregate several smaller address blocks into a larger block for more efficient routing.

this process is called address aggregation, helping reduce routing table size.

Question 24

What is the minimum header size of an IPv4 packet (without options)?
A) 8 bytes
B) 16 bytes
C) 20 bytes
D) 24 bytes

Answer 24

C) 20 bytes

The default IPv4 header is 20 bytes, including source/destination addresses, version, TTL, and other essential fields.

Question 25

The TTL (Time to Live) field in the IPv4 header limits how many routers a packet can pass through.

Answer 25

True Each router decrements TTL; when it reaches 0, the packet is discarded, preventing loops.

Question 26

Which field in the IPv4 header identifies which transport-layer protocol (e.g., TCP or UDP) should process the payload?

Answer 26

The Protocol field. The Protocol field in the IPv4 header specifies the upper-layer protocol to which the packet should be delivered.