Network LayerEasy
Q1. What is the size of an IPv4 address?
- A.64 bits
- B.128 bits
- C.16 bits
- D.32 bits✓ Correct
Explanation
An IPv4 address is 32 bits (4 bytes) long, typically written in dotted decimal notation (e.g., 192.168.1.1).
Network Layer
Topic in Computer Networks & Cloud Computing
210 total MCQsShowing 30 with explanations10 Easy10 Medium10 Hard
About This Topic
The network layer moves packets from source host to destination host across multiple networks, handling logical IP addressing, routing and forwarding. Typical questions ask about 32-bit IPv4 and 128-bit IPv6 addresses, address classes and private ranges, subnet masks, CIDR notation and calculating usable hosts in a subnet. Routing items contrast static and dynamic routes, distance-vector protocols like RIP with link-state protocols like OSPF, and the role of BGP between autonomous systems. Also be ready for IP fragmentation and the TTL field, broadcast versus multicast addresses, NAT, ICMP, and how a router chooses the next hop using longest-prefix matching.
Below are 30 practice questions from a pool of 210 Network Layer MCQs, one of 10 topics in Computer Networks & Cloud Computing. Each shows the correct answer with an explanation; when you are ready, take a timed quiz to test recall under exam conditions.
Practice Questions
Each question below shows the correct answer with a full explanation. Use these to build conceptual understanding before attempting a timed quiz.
Network LayerEasy
Q2. What is the main function of a router?
- A.Storing web pages on servers
- B.Forwarding packets between networks✓ Correct
- C.Providing wireless network access
- D.Connecting devices within a LAN
Explanation
A router's main function is to forward packets from one network to another by examining the destination IP address and consulting its routing table.
Network LayerEasy
Q3. Which class of IPv4 addresses is used for multicasting?
- A.Class B
- B.Class D✓ Correct
- C.Class C
- D.Class A
Explanation
Class D addresses (224.0.0.0 to 239.255.255.255) are reserved for multicast groups.
Network LayerEasy
Q4. What does the TTL field in an IP header stand for?
- A.Transfer Type Label
- B.Transmission Time Limit
- C.Total Transfer Length
- D.Time to Live✓ Correct
Explanation
TTL (Time to Live) limits the lifespan of a packet. Each router decrements it by 1, and when it reaches 0, the packet is discarded to prevent infinite loops.
Network LayerEasy
Q5. Which protocol is used to send error messages at the network layer?
- A.UDP
- B.TCP
- C.ARP
- D.ICMP✓ Correct
Explanation
ICMP (Internet Control Message Protocol) is used to send error messages and operational information, such as destination unreachable or time exceeded.
Network LayerEasy
Q6. What is the default subnet mask for a Class C IPv4 address?
- A.255.255.0.0
- B.255.255.255.255
- C.255.0.0.0
- D.255.255.255.0✓ Correct
Explanation
Class C addresses have a default subnet mask of 255.255.255.0, meaning the first 24 bits identify the network and the last 8 bits identify the host.
Network LayerEasy
Q7. Which IP address range is reserved for loopback testing?
- A.169.254.0.0/16
- B.127.0.0.0/8✓ Correct
- C.10.0.0.0/8
- D.192.168.0.0/16
Explanation
The address range 127.0.0.0/8 is reserved for loopback. The most commonly used loopback address is 127.0.0.1.
Network LayerEasy
Q8. What tool uses ICMP echo requests to test connectivity?
- A.traceroute
- B.nslookup
- C.ping✓ Correct
- D.netstat
Explanation
The ping command uses ICMP echo request and echo reply messages to test whether a remote host is reachable.
Network LayerEasy
Q9. Which of the following is a private IPv4 address?
- A.11.0.0.1
- B.172.32.0.1
- C.8.8.8.8
- D.192.168.1.1✓ Correct
Explanation
192.168.1.1 is a private IP address. Private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
Network LayerEasy
Q10. What is the purpose of NAT (Network Address Translation)?
- A.To translate private IPs to public IPs✓ Correct
- B.To compress packets for transfer
- C.To assign domain names to hosts
- D.To encrypt data during transit
Explanation
NAT translates private (internal) IP addresses to public (external) IP addresses, allowing multiple devices to share a single public IP address.
Network LayerMedium
Q11. In CIDR notation, what does /28 mean?
- A.28 hosts are available on subnet
- B.28 bits are for network addressing✓ Correct
- C.28 bits are for host addressing
- D.28 subnets exist in the network
Explanation
In CIDR notation, /28 means the first 28 bits of the address are used for the network portion, leaving 4 bits for host addresses (14 usable hosts).
Network LayerMedium
Q12. How many usable host addresses are available in a /26 subnet?
- A.64
- B.30
- C.62✓ Correct
- D.126
Explanation
A /26 subnet has 6 host bits: 2^6 = 64 total addresses. Subtracting the network address and broadcast address gives 62 usable host addresses.
Network LayerMedium
Q13. Which routing protocol uses the Bellman-Ford algorithm?
- A.RIP✓ Correct
- B.OSPF
- C.BGP
- D.IS-IS
Explanation
RIP (Routing Information Protocol) uses the Bellman-Ford (distance vector) algorithm to determine the best path based on hop count.
Network LayerMedium
Q14. What is the maximum hop count in RIP?
- A.255
- B.16
- C.15✓ Correct
- D.8
Explanation
RIP uses a maximum hop count of 15. A hop count of 16 means the destination is unreachable, limiting RIP to small networks.
Network LayerMedium
Q15. OSPF is classified as which type of routing protocol?
- A.Path vector
- B.Link-state✓ Correct
- C.Distance vector
- D.Hybrid
Explanation
OSPF (Open Shortest Path First) is a link-state routing protocol that uses Dijkstra's algorithm to compute the shortest path.
Network LayerMedium
Q16. What is the size of an IPv6 address?
- A.64 bits
- B.32 bits
- C.128 bits✓ Correct
- D.96 bits
Explanation
An IPv6 address is 128 bits (16 bytes) long, written as eight groups of four hexadecimal digits separated by colons.
Network LayerMedium
Q17. What is the count-to-infinity problem associated with?
- A.Link-state protocols
- B.Distance vector protocols✓ Correct
- C.Static routing tables
- D.Path vector protocols
Explanation
The count-to-infinity problem occurs in distance vector routing protocols where routers slowly increment the distance to an unreachable network, causing slow convergence.
Network LayerMedium
Q18. Which field in the IPv4 header is used for fragmentation reassembly?
- A.Header checksum field
- B.Identification field✓ Correct
- C.Protocol field
- D.TTL field
Explanation
The Identification field, along with Flags and Fragment Offset, is used to identify fragments belonging to the same original datagram for reassembly.
Network LayerMedium
Q19. What does DHCP provide?
- A.Automatic IP address assignment✓ Correct
- B.Email delivery management
- C.Routing information exchange
- D.Domain name resolution services
Explanation
DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses, subnet masks, default gateways, and other network configuration to devices.
Network LayerMedium
Q20. Which protocol is used between autonomous systems on the Internet?
- A.RIP
- B.EIGRP
- C.BGP✓ Correct
- D.OSPF
Explanation
BGP (Border Gateway Protocol) is the standard exterior gateway protocol used to exchange routing information between autonomous systems on the Internet.
Network LayerHard
Q21. Given the IP address 172.16.45.14/21, what is the network address?
- A.172.16.32.0
- B.172.16.40.0✓ Correct
- C.172.16.45.0
- D.172.16.44.0
Explanation
With /21, the mask is 255.255.248.0. The third octet 45 in binary is 00101101. ANDing with 11111000 gives 00101000 = 40. So the network is 172.16.40.0.
Network LayerHard
Q22. In OSPF, what is an Area Border Router (ABR)?
- A.A router that runs the BGP protocol
- B.A router operating within a single OSPF area
- C.A router connecting two or more OSPF areas✓ Correct
- D.A router connecting to external networks only
Explanation
An ABR connects two or more OSPF areas, including the backbone area (Area 0). It maintains separate link-state databases for each area.
Network LayerHard
Q23. What technique does split horizon use to solve the count-to-infinity problem?
- A.Not advertising routes back through learned interfaces✓ Correct
- B.Using TTL values to limit the route propagation
- C.Sending updates to directly connected routers only
- D.Encrypting all routing update messages sent
Explanation
Split horizon prevents a router from advertising a route back through the interface from which the route was originally learned, helping to prevent routing loops.
Network LayerHard
Q24. In IPv6, what replaces broadcast?
- A.No replacement exists
- B.Multicast and anycast✓ Correct
- C.Unicast addressing
- D.Simplex mode
Explanation
IPv6 eliminates broadcast addressing. Its functionality is replaced by multicast (to multiple specific hosts) and anycast (to the nearest host in a group).
Network LayerHard
Q25. What is the purpose of the OSPF Designated Router (DR)?
- A.To connect to external autonomous systems
- B.To serve as the default gateway for hosts
- C.To handle DHCP requests from all clients
- D.To reduce adjacencies on multi-access networks✓ Correct
Explanation
The DR reduces adjacencies on multi-access networks. Instead of every router forming adjacencies with every other router, all routers form adjacencies only with the DR and BDR.
Network LayerHard
Q26. A company needs to create 6 subnets from a /24 network. What is the most efficient subnet mask to use?
- A./29
- B./26
- C./28
- D./27✓ Correct
Explanation
To create 6 subnets, we need at least 3 borrowed bits (2^3 = 8 subnets >= 6). Starting from /24, borrowing 3 bits gives /27 with 30 usable hosts per subnet.
Network LayerHard
Q27. What is the function of the Protocol field in the IPv4 header?
- A.To indicate the total length of the packet
- B.To identify the upper-layer protocol used✓ Correct
- C.To store the header checksum for errors
- D.To specify the version of IP being used
Explanation
The Protocol field identifies the upper-layer protocol encapsulated in the IP datagram. TCP is 6, UDP is 17, ICMP is 1, and OSPF is 89.
Network LayerHard
Q28. In BGP, what is the AS_PATH attribute used for?
- A.Listing traversed ASes to prevent loops✓ Correct
- B.Measuring the link bandwidth capacity
- C.Encrypting routing updates over links
- D.Assigning IP addresses to BGP peers
Explanation
AS_PATH lists all autonomous systems a route advertisement has traversed. It is used for loop prevention (a router rejects routes containing its own AS number) and path selection.
Network LayerHard
Q29. What is the main advantage of VLSM (Variable Length Subnet Masking)?
- A.It enables faster packet routing overall
- B.It simplifies network configuration greatly
- C.It provides better security for subnets
- D.It allows subnets of different sizes for efficiency✓ Correct
Explanation
VLSM allows different subnets to have different sizes (subnet masks), enabling more efficient use of IP address space by matching subnet size to actual needs.
Network LayerHard
Q30. What is route aggregation (supernetting) and why is it important?
- A.Combining network prefixes to reduce routing tables✓ Correct
- B.Assigning multiple IP addresses to a single host
- C.Creating backup routes for network redundancy
- D.Splitting a network into smaller subnets for isolation
Explanation
Route aggregation (supernetting) combines contiguous network prefixes into a single summary route, reducing the size of routing tables and improving router efficiency.
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