Computer Networking EXAM 2025 | ACTUAL REAL EXAM ACCURATE QUESTIONS AND ANSWERS WITH RATIONALES | VERIFIED AND LATEST UPDATED |GUARANTEED PASS

What are the two most important network-layer functions in a datagram network? What are the three most important network-layer functions in a virtual-circuit network? A. Routing, Encryption, Authentication B. Path determination, Switching, and Call setup (for VC network) C. Framing, Transmission, Compression D. IP Addressing, ARP Resolution, Port Mapping Correct Answer: B Rationale: In datagram networks, the key functions are path determination and switching. Virtual-circuit networks add the function of call setup to establish a pre-defined route. What is the difference between routing and forwarding? A. Routing happens in Layer 1; forwarding in Layer 3 B. Routing is used only in wireless; forwarding is for wired networks C. Forwarding moves packets from input to output; routing determines the path D. Routing is a physical layer function; forwarding is a software feature Correct Answer: C Rationale: Routing determines the path a packet will take from source to destination, while forwarding moves packets to the correct output interface. Do routers in both datagram networks and virtual-circuit networks use forwarding tables? A. No, only virtual-circuit routers use them B. Yes, but only for IPv6 traffic C. Yes, both use forwarding tables specific to their architecture D. Only backbone routers use forwarding tables Correct Answer: C Rationale: Both types of networks use forwarding tables—datagram networks for best-effort delivery, VC networks for predefined routes. Which hypothetical services could be provided by the network layer to a single packet and a flow of packets? A. DNS resolution and ARP caching B. Guaranteed delivery, bandwidth, jitter control C. Firewall and proxy filtering D. SSL encryption and MAC filtering Correct Answer: B Rationale: Network layers could hypothetically offer services such as guaranteed delivery and delay, bandwidth, and jitter control, though not all are supported by IP. Which applications benefit most from ATM's CBR service model? A. Email and file transfer B. Video conferencing and real-time voice C. DNS lookups and ARP resolution D. Web browsing and HTTP downloads Correct Answer: B Rationale: ATM’s CBR service provides guaranteed bandwidth and timing, ideal for timesensitive applications like voice and video. Why does each input port in a high-speed router store a shadow copy of the forwarding table? A. To reduce energy consumption B. To allow decentralized and faster forwarding decisions C. To share data with the output port D. To ensure table consistency across networks Correct Answer: B Rationale: Shadow copies enable each input port to make local decisions without involving a central processor, reducing bottlenecks. Which switching fabric types can forward multiple packets in parallel? A. Only switching via memory B. Only switching via a bus C. Switching via an interconnection network D. All types support parallel forwarding Correct Answer: C Rationale: Only switching via an interconnection network can handle multiple packets simultaneously. How can packet loss at input ports be eliminated (without infinite buffers)? A. Increase router RAM B. Use NAT C. Make switching fabric at least n times faster than input line speed D. Decrease packet size Correct Answer: C Rationale: Fast switching prevents queue build-up and buffer overflow, which reduces packet loss. What is Head-of-Line (HOL) blocking, and where does it occur? A. When routing tables loop indefinitely; occurs at output B. When a packet blocks others behind it; occurs at input C. When NAT fails; occurs at firewall D. When ARP requests fail; occurs at router Correct Answer: B Rationale: HOL blocking happens when the first packet in line is blocked, delaying all behind it, at the input port. Do routers have IP addresses, and if so, how many? A. No, they use MAC addresses B. Yes, one per network interface C. Yes, only one for the entire router D. No, they rely on switch-level addressing Correct Answer: B Rationale: Routers have an IP address for each interface connected to a network. What is the 32-bit binary equivalent of the IP address 223.1.3.27? A. B. C. D. Correct Answer: B Rationale: The IP address converts to in binary. How are IP addresses assigned to multiple PCs connected to a home router? A. Manually using static IPs B. Each gets a public IP from ISP C. Through DHCP provided by the router D. Each uses a loopback address Correct Answer: C Rationale: The router assigns local private IPs using DHCP and uses NAT to share one public IP from the ISP. How many interfaces and forwarding tables are involved when an IP datagram passes through 3 routers? A. 4 interfaces, 1 table B. 6 interfaces, 2 tables C. 8 interfaces, 3 tables D. 10 interfaces, 5 tables Correct Answer: C Rationale: Each router has two interfaces, and one at the source and destination. Thus, 4 routers = 8 interfaces, and each router uses one forwarding table. What percentage of a datagram is overhead if 40-byte chunks are encapsulated in IP/TCP headers? A. 20% B. 30% C. 50% D. 70% Correct Answer: C Rationale: TCP and IP headers together are about 40 bytes; if the application sends 40 bytes, then 50% of the datagram is overhead. How does Host B know to pass the payload to TCP or UDP? A. MAC address of the sender B. IP address in the header C. Protocol field in the IP header D. Destination port number Correct Answer: C Rationale: The 8-bit protocol field in the IP header indicates whether the segment should go to TCP, UDP, or another protocol. Does IPv6 treat IPv4 tunnels as link-layer protocols? A. No, it’s just an encapsulation trick B. Yes, when tunneled, IPv4 is treated as link layer C. No, IPv6 doesn’t support tunneling D. Yes, IPv6 discards all IPv4 fields Correct Answer: B Rationale: When IPv6 tunnels through IPv4, the IPv4 network is treated like a virtual link layer. Compare and contrast link-state and distance-vector routing. A. LS is distributed, DV is centralized B. LS requires neighbors to advertise; DV does not C. LS has global knowledge, DV only local D. Both operate only in wireless networks Correct Answer: C Rationale: Link-state algorithms use global knowledge of the network, while distance-vector uses information from immediate neighbors. Why is the Internet's hierarchical structure scalable? A. It removes the need for routers B. Routers use encryption instead of routing C. Routers are grouped into ASs, which simplifies routing D. Each host is responsible for its own routing Correct Answer: C Rationale: By grouping routers into ASs and using separate intra- and inter-AS protocols, routing is more scalable. Is it necessary for all ASes to use the same intra-AS protocol? A. Yes, to maintain global routing B. No, each AS can choose its own protocol C. Only for ASes connected to Tier-1 networks D. Yes, BGP requires it Correct Answer: B Rationale: Each AS has administrative autonomy and may use RIP, OSPF, or other protocols internally. Compare advertisements used by RIP and OSPF. A. RIP advertises to all; OSPF advertises to neighbors B. OSPF advertises all links to all routers; RIP advertises routing tables to neighbors C. Both advertise only hop counts D. OSPF uses TCP; RIP uses UDP Correct Answer: B Rationale: OSPF floods link-state information to all routers in the AS, while RIP only sends routing tables to neighbors. RIP uses hop counts; what does BGP advertise? A. MAC addresses B. DNS mappings C. Sequence of ASs on the routes D. Network topology Correct Answer: C Rationale: BGP announces routes using the AS-PATH, which is a sequence of ASs that packets must traverse. Define and contrast subnet, prefix, and BGP route. A. All refer to the same part of an IP address B. Subnet = MAC, Prefix = DNS, Route = NAT C. Subnet is part of a network; prefix is network ID; route is prefix + attributes D. Subnet is physical; prefix is logical; route is virtual Correct Answer: C Rationale: A subnet is a portion of the network; prefix defines the network; a BGP route includes a prefix and its attributes. How does BGP use NEXT-HOP and AS-PATH? A. NEXT-HOP identifies routers, AS-PATH tracks packet loss B. AS-PATH for routing decisions and loops, NEXT-HOP for next destination IP C. NEXT-HOP encrypts packets, AS-PATH compresses them D. NEXT-HOP stores DNS records, AS-PATH stores MAC addresses Correct Answer: B Rationale: AS-PATH helps prevent loops and influence path selection; NEXT-HOP tells the next router to forward to. How can ISP B implement policy using BGP? A. Refuse to route any traffic B. Only advertise selected paths to peers C. Always route based on hop count D. Use static routes only Correct Answer: B Rationale: By controlling which routes are advertised, ISP B can enforce routing policy (e.g., no transit traffic between peers). What is the main disadvantage of implementing broadcast via multiple unicasts? A. It's faster B. It provides guaranteed delivery C. It’s inefficient and redundant D. It uses less bandwidth Correct Answer: C Rationale: Sending multiple copies of the same message creates inefficiencies in bandwidth and processing