CS 6250 Computer Networks Final Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf.
1. Which statement most accurately describes the primary purpose of
the Internet Protocol (IP) layer in a computer network, particularly in
relation to the services provided by lower and higher layers?
A. It guarantees reliable, ordered, duplicate-free delivery of application data
between endpoints
B. It provides logical addressing and forwarding of packets across
interconnected networks without inherently guaranteeing reliable delivery
C. It establishes end-to-end encryption for every application communicating
over the Internet
D. It allocates application ports and establishes persistent sessions between
client and server processes
Rationale: The IP layer is responsible for logical addressing and packet
forwarding across interconnected networks. IP itself is fundamentally a
best-effort, connectionless service and does not guarantee reliable,
ordered delivery; those properties may be provided by higher-layer
protocols such as TCP.
2. In a packet-switched network, what is the most important distinction
between a forwarding decision and a routing decision?
,A. Forwarding determines the complete end-to-end path, whereas routing
determines only the outgoing interface
B. Forwarding occurs at hosts only, whereas routing occurs exclusively at
switches
C. Forwarding uses a router's forwarding table to select the next hop,
whereas routing computes or learns paths and constructs the information
used for forwarding
D. Forwarding is performed by TCP, whereas routing is performed by IP
Rationale: Routing is the control-plane process that determines
reachability and paths, while forwarding is the data-plane process that
uses the resulting forwarding information to move individual packets
toward their destinations.
3. Which routing protocol is classified as an interior gateway protocol
that uses a link-state algorithm and traditionally computes shortest
paths using Dijkstra's algorithm?
A. BGP
B. RIP
C. OSPF
D. SMTP
Rationale: OSPF is an interior gateway protocol based on link-state
routing. Routers distribute link-state information and independently
compute shortest paths using Dijkstra's shortest-path algorithm.
4. A router running a distance-vector routing protocol receives from
neighbor R2 a distance vector indicating that R2 can reach destination
network X with a cost of 4. If the cost of the link from the receiving
router to R2 is 2, what route cost should the receiving router calculate
for reaching X through R2?
A. 2
B. 4
,C. 6
D. 8
Rationale: In distance-vector routing, the cost of a route through a
neighbor is the neighbor's advertised distance plus the local cost of
reaching that neighbor. Therefore, the calculated cost is 2 + 4 = 6.
5. Which phenomenon is most directly associated with the classic count-
to-infinity problem in distance-vector routing?
A. Routers repeatedly advertise increasingly large path costs because they
lack complete knowledge of the network topology
B. Routers encrypt routing advertisements using progressively stronger
cryptographic algorithms
C. Routers permanently eliminate all routes after receiving a single invalid
packet
D. Routers independently compute identical link-state databases without
exchanging updates
Rationale: The count-to-infinity problem occurs because distance-vector
routers have incomplete global topology information and can incorrectly
route traffic through one another after a failure, causing their advertised
metrics to increase iteratively.
6. Which technique is specifically designed to reduce routing loops
associated with the count-to-infinity problem in distance-vector
protocols?
A. Split horizon
B. Packet fragmentation
C. Random early detection
D. Carrier sensing
Rationale: Split horizon prevents a router from advertising a route back
through the interface from which that route was learned, thereby reducing
the possibility of two routers misleading one another about reachability.
, 7. Which characteristic most accurately distinguishes a link-state routing
protocol from a traditional distance-vector protocol?
A. Link-state routers know only the distance to directly connected neighbors
B. Link-state routers distribute information about network links and
construct a topology database from which paths are computed
C. Link-state routers never exchange routing information after initialization
D. Link-state routing eliminates the need for forwarding tables
Rationale: Link-state protocols distribute information describing network
links, allowing routers to build a topology database and independently
calculate shortest paths. Distance-vector protocols instead exchange
destination-distance information with neighbors.
8. In OSPF, why are areas used in large networks?
A. To prevent routers from using IP addresses
B. To eliminate the need for shortest-path computation
C. To improve scalability by limiting the scope of topology information and
reducing computational and control overhead
D. To convert OSPF into a transport-layer protocol
Rationale: OSPF areas provide hierarchical organization. By limiting
detailed link-state information to areas and using summarized information
between areas, OSPF reduces the amount of state and computation
required by routers.
9. Which routing protocol is primarily responsible for exchanging
reachability information between autonomous systems on the
Internet?
A. OSPF
B. RIP
C. BGP
D. ARP
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf.
1. Which statement most accurately describes the primary purpose of
the Internet Protocol (IP) layer in a computer network, particularly in
relation to the services provided by lower and higher layers?
A. It guarantees reliable, ordered, duplicate-free delivery of application data
between endpoints
B. It provides logical addressing and forwarding of packets across
interconnected networks without inherently guaranteeing reliable delivery
C. It establishes end-to-end encryption for every application communicating
over the Internet
D. It allocates application ports and establishes persistent sessions between
client and server processes
Rationale: The IP layer is responsible for logical addressing and packet
forwarding across interconnected networks. IP itself is fundamentally a
best-effort, connectionless service and does not guarantee reliable,
ordered delivery; those properties may be provided by higher-layer
protocols such as TCP.
2. In a packet-switched network, what is the most important distinction
between a forwarding decision and a routing decision?
,A. Forwarding determines the complete end-to-end path, whereas routing
determines only the outgoing interface
B. Forwarding occurs at hosts only, whereas routing occurs exclusively at
switches
C. Forwarding uses a router's forwarding table to select the next hop,
whereas routing computes or learns paths and constructs the information
used for forwarding
D. Forwarding is performed by TCP, whereas routing is performed by IP
Rationale: Routing is the control-plane process that determines
reachability and paths, while forwarding is the data-plane process that
uses the resulting forwarding information to move individual packets
toward their destinations.
3. Which routing protocol is classified as an interior gateway protocol
that uses a link-state algorithm and traditionally computes shortest
paths using Dijkstra's algorithm?
A. BGP
B. RIP
C. OSPF
D. SMTP
Rationale: OSPF is an interior gateway protocol based on link-state
routing. Routers distribute link-state information and independently
compute shortest paths using Dijkstra's shortest-path algorithm.
4. A router running a distance-vector routing protocol receives from
neighbor R2 a distance vector indicating that R2 can reach destination
network X with a cost of 4. If the cost of the link from the receiving
router to R2 is 2, what route cost should the receiving router calculate
for reaching X through R2?
A. 2
B. 4
,C. 6
D. 8
Rationale: In distance-vector routing, the cost of a route through a
neighbor is the neighbor's advertised distance plus the local cost of
reaching that neighbor. Therefore, the calculated cost is 2 + 4 = 6.
5. Which phenomenon is most directly associated with the classic count-
to-infinity problem in distance-vector routing?
A. Routers repeatedly advertise increasingly large path costs because they
lack complete knowledge of the network topology
B. Routers encrypt routing advertisements using progressively stronger
cryptographic algorithms
C. Routers permanently eliminate all routes after receiving a single invalid
packet
D. Routers independently compute identical link-state databases without
exchanging updates
Rationale: The count-to-infinity problem occurs because distance-vector
routers have incomplete global topology information and can incorrectly
route traffic through one another after a failure, causing their advertised
metrics to increase iteratively.
6. Which technique is specifically designed to reduce routing loops
associated with the count-to-infinity problem in distance-vector
protocols?
A. Split horizon
B. Packet fragmentation
C. Random early detection
D. Carrier sensing
Rationale: Split horizon prevents a router from advertising a route back
through the interface from which that route was learned, thereby reducing
the possibility of two routers misleading one another about reachability.
, 7. Which characteristic most accurately distinguishes a link-state routing
protocol from a traditional distance-vector protocol?
A. Link-state routers know only the distance to directly connected neighbors
B. Link-state routers distribute information about network links and
construct a topology database from which paths are computed
C. Link-state routers never exchange routing information after initialization
D. Link-state routing eliminates the need for forwarding tables
Rationale: Link-state protocols distribute information describing network
links, allowing routers to build a topology database and independently
calculate shortest paths. Distance-vector protocols instead exchange
destination-distance information with neighbors.
8. In OSPF, why are areas used in large networks?
A. To prevent routers from using IP addresses
B. To eliminate the need for shortest-path computation
C. To improve scalability by limiting the scope of topology information and
reducing computational and control overhead
D. To convert OSPF into a transport-layer protocol
Rationale: OSPF areas provide hierarchical organization. By limiting
detailed link-state information to areas and using summarized information
between areas, OSPF reduces the amount of state and computation
required by routers.
9. Which routing protocol is primarily responsible for exchanging
reachability information between autonomous systems on the
Internet?
A. OSPF
B. RIP
C. BGP
D. ARP
