1What is the primary purpose of TCP Congestion Control?
TCP Congestion Control
Easy
A.To assign IP addresses to devices on a network
B.To increase the speed of data transmission irrespective of network state
C.To prevent network collapse by regulating the rate at which packets are sent
D.To encrypt data packets before transmission
Correct Answer: To prevent network collapse by regulating the rate at which packets are sent
Explanation:
TCP Congestion Control helps prevent congestion collapse by adjusting the sender's transmission rate based on perceived network conditions.
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2Which phase of TCP congestion control exponentially increases the congestion window size?
TCP Congestion Control
Easy
A.Slow Start
B.Fast Recovery
C.Congestion Avoidance
D.Fast Retransmit
Correct Answer: Slow Start
Explanation:
In the Slow Start phase, the TCP congestion window size doubles every round trip time (RTT), leading to exponential growth.
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3What happens to the congestion window when a timeout occurs in TCP Tahoe?
TCP Congestion Control
Easy
A.It is doubled
B.It remains unchanged
C.It is halved
D.It is reduced to 1 Maximum Segment Size (MSS)
Correct Answer: It is reduced to 1 Maximum Segment Size (MSS)
Explanation:
When a timeout occurs, indicating severe congestion, TCP reduces the congestion window to 1 MSS and restarts the slow start process.
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4Which of the following relies on routers to provide direct feedback to senders about network congestion?
Network assistance Congestion Control Algorithms
Easy
A.Network-assisted congestion control
B.End-to-end congestion control
C.Error control
D.Flow control
Correct Answer: Network-assisted congestion control
Explanation:
In network-assisted congestion control, routers provide explicit feedback (like a choke packet or an ECN bit) to the sender about the congestion state.
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5What is the length of an IPv4 address?
NETWORK LAYER: IP Addressing
Easy
A.32 bits
B.128 bits
C.64 bits
D.16 bits
Correct Answer: 32 bits
Explanation:
An IPv4 address is 32 bits long, typically written in dotted-decimal notation.
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6Which of the following identifies the specific device on a given network in an IP address?
NETWORK LAYER: IP Addressing
Easy
A.Subnet Mask
B.Host ID
C.Default Gateway
D.Network ID
Correct Answer: Host ID
Explanation:
An IP address is split into a Network ID (identifying the network) and a Host ID (identifying the specific device on that network).
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7In Classful IP addressing, which class is reserved for multicast addresses?
IP Addressing Both Classfull and Classless
Easy
A.Class A
B.Class B
C.Class D
D.Class C
Correct Answer: Class D
Explanation:
Class D IP addresses (ranging from 224.0.0.0 to 239.255.255.255) are strictly reserved for multicast groups.
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8What does CIDR stand for in the context of IP addressing?
IP Addressing Both Classfull and Classless
Easy
A.Classless Internal Data Routing
B.Classful Internet Data Routing
C.Computer Inter-Domain Routing
D.Classless Inter-Domain Routing
Correct Answer: Classless Inter-Domain Routing
Explanation:
CIDR stands for Classless Inter-Domain Routing, a method for allocating IP addresses and IP routing that replaces the older classful network architecture.
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9Which IP class has a default subnet mask of 255.255.0.0?
IP Addressing Both Classfull and Classless
Easy
A.Class B
B.Class D
C.Class A
D.Class C
Correct Answer: Class B
Explanation:
Class B networks use the first 16 bits for the network ID, resulting in a default subnet mask of 255.255.0.0.
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10What is the primary purpose of subnetting?
Subnetting and Supernetting
Easy
A.To divide a single large network into multiple smaller logical networks
B.To combine multiple small networks into one large network
C.To encrypt IP addresses
D.To assign MAC addresses to devices
Correct Answer: To divide a single large network into multiple smaller logical networks
Explanation:
Subnetting allows a large network to be logically divided into smaller, more manageable sub-networks, improving performance and security.
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11Which process is the exact opposite of subnetting?
Subnetting and Supernetting
Easy
A.Switching
B.Supernetting
C.Multiplexing
D.Routing
Correct Answer: Supernetting
Explanation:
Supernetting (or route summarization) combines multiple contiguous small networks into a single larger network, the opposite of subnetting.
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12If a network has a CIDR notation of /24, how many bits are used for the Network ID?
Subnetting examples
Easy
A.24 bits
B.8 bits
C.16 bits
D.32 bits
Correct Answer: 24 bits
Explanation:
The number after the slash in CIDR notation (e.g., /24) indicates the exact number of bits used for the Network ID.
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13Which of the following represents the broadcast address of a network?
Subnetting examples
Easy
A.All network bits are set to 0
B.All network bits are set to 1
C.All host bits are set to 1
D.All host bits are set to 0
Correct Answer: All host bits are set to 1
Explanation:
In an IPv4 network, the address where all host bits are set to binary 1 is reserved as the directed broadcast address for that subnet.
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14Which of the following is a primary function of the Network Layer?
Network layer services
Easy
A.Framing data bits into frames
B.Ensuring reliable end-to-end data delivery
C.Error detection on a single link
D.Routing packets from source to destination
Correct Answer: Routing packets from source to destination
Explanation:
The Network Layer is responsible for routing data packets from a source host to a destination host across multiple networks.
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15Is the standard IP protocol connection-oriented or connectionless?
Network layer services
Easy
A.Neither
B.Connection-oriented
C.Connectionless
D.Both
Correct Answer: Connectionless
Explanation:
The Internet Protocol (IP) at the Network Layer is a connectionless service, meaning each packet is treated independently without prior setup.
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16What does 'packet loss' refer to in a network?
Network layer performance
Easy
A.Packets failing to reach their destination
B.Packets taking different routes to the destination
C.Packets arriving faster than they can be processed
D.Packets being converted into frames
Correct Answer: Packets failing to reach their destination
Explanation:
Packet loss occurs when one or more packets traveling across a network fail to reach their intended destination, often due to network congestion or errors.
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17Which term describes the time it takes for a packet to travel from source to destination?
Network layer performance
Easy
A.Bandwidth
B.Throughput
C.Delay (Latency)
D.Jitter
Correct Answer: Delay (Latency)
Explanation:
Delay, or latency, is the total time taken for a data packet to travel from the sender to the receiver across the network.
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18What is 'jitter' in the context of network performance?
Network layer performance
Easy
A.The complete loss of a network connection
B.The number of bits lost in transmission
C.The variation in packet delay
D.The total amount of data transmitted
Correct Answer: The variation in packet delay
Explanation:
Jitter refers to the variation in the delay of received packets, which is especially important for real-time applications like voice and video.
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19In TCP congestion control, what does three duplicate ACKs typically indicate?
TCP Congestion Control
Easy
A.The connection is closed
B.The sender's buffer is full
C.A packet has been lost, but the network is not heavily congested
D.The receiver has powered down
Correct Answer: A packet has been lost, but the network is not heavily congested
Explanation:
Three duplicate ACKs indicate that a specific packet was lost (likely dropped), but subsequent packets are still arriving, which triggers a Fast Retransmit instead of a full slow start.
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20Which component is necessary for a host on one subnet to communicate with a host on a different subnet?
NETWORK LAYER: IP Addressing
Easy
A.Switch
B.Hub
C.Router (Default Gateway)
D.Repeater
Correct Answer: Router (Default Gateway)
Explanation:
A router (or default gateway) operates at the network layer and is required to route traffic between different subnets.
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21In a choke packet congestion control algorithm, how does a router typically react when it determines that congestion is approaching?
Network assistance Congestion Control Algorithms
Medium
A.It drops all incoming packets immediately.
B.It broadcasts a message to all adjacent routers to reroute traffic.
C.It sends a choke packet to the source, requesting it to reduce its sending rate.
D.It increases its queue size to accommodate more packets.
Correct Answer: It sends a choke packet to the source, requesting it to reduce its sending rate.
Explanation:
In the choke packet method, a router experiencing congestion sends a specific control packet (choke packet) directly to the source host to slow down its transmission rate.
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22During the TCP Slow Start phase, how does the congestion window () size increase for every ACK received?
TCP Congestion Control
Medium
A.Remains constant
B.Increases by half its previous value
C.Increases by 1 MSS
D.Increases exponentially
Correct Answer: Increases by 1 MSS
Explanation:
In TCP Slow Start, for every ACK received, the congestion window increases by 1 Maximum Segment Size (MSS), leading to an overall exponential growth per round-trip time.
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23If a TCP sender detects packet loss via three duplicate ACKs, what is its expected response in TCP Reno?
TCP Congestion Control
Medium
A.Ignore the duplicate ACKs and wait for a timeout.
B.Set to 1 MSS and enter Slow Start.
C.Increase exponentially to overcome the loss.
D.Halve the , set to this new value, and perform Fast Recovery.
Correct Answer: Halve the , set to this new value, and perform Fast Recovery.
Explanation:
TCP Reno responds to three duplicate ACKs by halving the congestion window, setting the slow start threshold to this value, and entering the Fast Recovery phase.
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24Which of the following is a valid IPv4 address that can be assigned to a host?
NETWORK LAYER: IP Addressing
Medium
A.172.16.50.50
B.192.168.1.0
C.127.0.0.1
D.255.255.255.255
Correct Answer: 172.16.50.50
Explanation:
172.16.50.50 is a valid host address. 127.0.0.1 is for loopback, 192.168.1.0 is a network address, and 255.255.255.255 is a broadcast address.
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25In Classful IP addressing, what is the default subnet mask for a Class B network?
IP Addressing Both Classfull and Classless
Medium
A.255.255.255.255
B.255.0.0.0
C.255.255.0.0
D.255.255.255.0
Correct Answer: 255.255.0.0
Explanation:
Class B networks use the first two octets for the network portion and the last two for the host portion, corresponding to a subnet mask of 255.255.0.0.
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26Which CIDR notation accurately represents the subnet mask 255.255.240.0?
IP Addressing Both Classfull and Classless
Medium
A./20
B./24
C./22
D./28
Correct Answer: /20
Explanation:
The subnet mask 255.255.240.0 has 8 + 8 + 4 = 20 bits set to 1, which corresponds to the /20 CIDR notation.
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27Supernetting is used primarily for which of the following purposes?
Subnetting and Supernetting
Medium
A.To allocate more host bits to a single Class C network.
B.To aggregate multiple smaller network routes into a single routing table entry.
C.To divide a large network into smaller, more manageable subnets.
D.To convert an IPv4 address into an IPv6 address.
Correct Answer: To aggregate multiple smaller network routes into a single routing table entry.
Explanation:
Supernetting (route summarization) combines multiple contiguous smaller networks into a larger network block to reduce the size of routing tables.
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28Given the IP address 192.168.10.45 with a subnet mask of 255.255.255.224, what is the network address?
Subnetting examples
Medium
A.192.168.10.64
B.192.168.10.45
C.192.168.10.0
D.192.168.10.32
Correct Answer: 192.168.10.32
Explanation:
The mask 255.255.255.224 (/27) gives a block size of 32. The multiples are 0, 32, 64. 45 falls in the 32 subnet, so the network address is 192.168.10.32.
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29If an organization needs 50 hosts per subnet, what is the most efficient subnet mask to use from a Class C network?
Subnetting examples
Medium
A.255.255.255.240
B.255.255.255.224
C.255.255.255.128
D.255.255.255.192
Correct Answer: 255.255.255.192
Explanation:
To support 50 hosts, we need . gives 62 usable hosts. Leaving 6 bits for the host leaves 2 bits for the subnet (in a Class C), resulting in a mask of 255.255.255.192.
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30Which of the following services is NOT typically provided by the Network Layer in the Internet model?
Network layer services
Medium
A.Fragmentation and reassembly
B.Reliable end-to-end data transfer
C.Logical addressing
D.Routing
Correct Answer: Reliable end-to-end data transfer
Explanation:
Reliable end-to-end data transfer is a function of the Transport layer (like TCP). The Network layer (IP) provides best-effort, connectionless delivery.
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31Which metric is most directly affected by a large number of hops between the source and destination in a packet-switched network?
Network layer performance
Medium
A.Bandwidth
B.End-to-end delay
C.Bit error rate
D.Throughput
Correct Answer: End-to-end delay
Explanation:
Each hop adds processing, queuing, transmission, and propagation delays, thereby directly increasing the total end-to-end delay of the network.
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32Random Early Detection (RED) is used in routers to prevent congestion. How does RED primarily function?
Network assistance Congestion Control Algorithms
Medium
A.By increasing the transmission rate of the links temporarily.
B.By calculating a drop probability based on average queue length and preemptively dropping or marking packets.
C.By sending explicit source quench messages to all connected hosts.
D.By randomly dropping packets only when the router's queue is completely full.
Correct Answer: By calculating a drop probability based on average queue length and preemptively dropping or marking packets.
Explanation:
RED monitors the average queue length and drops or marks packets with a certain probability before the queue gets completely full to implicitly signal the sender to slow down.
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33In TCP, what happens to the congestion window () and slow start threshold () upon experiencing a timeout?
TCP Congestion Control
Medium
A. is set to , and is doubled.
B.Both and are reset to 1 MSS.
C. is set to half of , and is set to 1 MSS.
D. is halved, and remains unchanged.
Correct Answer: is set to half of , and is set to 1 MSS.
Explanation:
When a timeout occurs, TCP assumes severe congestion. It sets the to half the current and resets to 1 MSS, restarting the Slow Start phase.
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34A host sends a packet to the address 255.255.255.255. What is the scope of this transmission?
NETWORK LAYER: IP Addressing
Medium
A.It is delivered only to the router connected to the sender.
B.It is sent to a specific multicast group.
C.It is routed to all hosts on the global Internet.
D.It is broadcasted to all hosts on the sender's local network.
Correct Answer: It is broadcasted to all hosts on the sender's local network.
Explanation:
The address 255.255.255.255 is the limited broadcast address, meaning the packet is intended for every host on the local physical network and is not forwarded by routers.
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35Why was Classless Inter-Domain Routing (CIDR) introduced?
IP Addressing Both Classfull and Classless
Medium
A.To provide encryption at the network layer.
B.To simplify the configuration of end hosts.
C.To alleviate the rapid depletion of IPv4 addresses and reduce routing table sizes.
D.To replace IPv4 with IPv6.
Correct Answer: To alleviate the rapid depletion of IPv4 addresses and reduce routing table sizes.
Explanation:
CIDR replaced the rigid classful boundaries (Classes A, B, C) with variable-length subnet masking, which allowed for more efficient allocation of IP addresses and route aggregation.
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36Which of the following conditions must be met for a set of networks to be aggregated into a single supernet?
Subnetting and Supernetting
Medium
A.The network blocks must be contiguous and the number of networks must be a power of 2.
B.The network blocks must be physically located in the same geographic region.
C.The subnet masks must be different for each network block.
D.The network blocks must all be Class A networks.
Correct Answer: The network blocks must be contiguous and the number of networks must be a power of 2.
Explanation:
For valid route aggregation (supernetting), the IP address blocks must be contiguous, the number of blocks must be a power of 2, and the blocks must share a common high-order bit prefix.
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37A company has the network block 200.10.20.0/24 and needs to divide it into subnets that support up to 14 hosts each. Which subnet mask should be used?
Subnetting examples
Medium
A.255.255.255.252
B.255.255.255.248
C.255.255.255.224
D.255.255.255.240
Correct Answer: 255.255.255.240
Explanation:
To support 14 hosts, you need 4 host bits (). This leaves 28 bits for the network part (/28). A /28 prefix corresponds to a subnet mask of 255.255.255.240.
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38In the context of the network layer, what is the primary function of the forwarding table (or MAC table in some contexts, but routing table here) inside a router?
Network layer services
Medium
A.To translate domain names to IP addresses.
B.To ensure reliable end-to-end data transmission.
C.To encrypt data packets before transmission.
D.To map destination IP addresses to outgoing interfaces.
Correct Answer: To map destination IP addresses to outgoing interfaces.
Explanation:
The forwarding table in a router maps incoming packets' destination IP addresses to the appropriate outgoing link interfaces so they can reach their next hop.
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39If a router's arrival rate of packets exceeds its processing and transmission capacity over an extended period, what is the most likely consequence?
Network layer performance
Medium
A.Packets will experience infinite queuing delay and eventually be dropped.
B.The router will convert the packet payloads to a smaller size.
C.The router will automatically upgrade its bandwidth.
D.The end-to-end delay will become exactly zero.
Correct Answer: Packets will experience infinite queuing delay and eventually be dropped.
Explanation:
If arrival rate > processing rate for a sustained time, the router's buffer will fill up. Subsequent packets will be dropped, and queuing delay will grow massively.
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40What is the broadcast address for the subnet 10.1.1.64/26?
Subnetting examples
Medium
A.10.1.1.255
B.10.1.1.63
C.10.1.1.128
D.10.1.1.127
Correct Answer: 10.1.1.127
Explanation:
A /26 subnet mask gives a block size of 64 (). The subnets are 0, 64, 128, etc. For the 64 subnet, the next subnet is 128, so the broadcast address is 128 - 1 = 127, making it 10.1.1.127.
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41In TCP Reno, assuming a connection is in the Congestion Avoidance phase with a congestion window (cwnd) of 32 MSS. If 3 duplicate ACKs are received, what will be the new values of ssthresh and cwnd immediately after the fast recovery algorithm is initiated?
TCP Congestion Control
Hard
A.ssthresh = 32 MSS, cwnd = 16 MSS
B.ssthresh = 16 MSS, cwnd = 1 MSS
C.ssthresh = 16 MSS, cwnd = 16 MSS
D.ssthresh = 16 MSS, cwnd = 19 MSS
Correct Answer: ssthresh = 16 MSS, cwnd = 19 MSS
Explanation:
In TCP Reno, upon receiving 3 duplicate ACKs, ssthresh is set to half of the current cwnd ( MSS). cwnd is then set to ssthresh + 3 MSS to account for the 3 segments that have left the network and triggered the duplicate ACKs, making cwnd = MSS.
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42An ISP is granted a block of addresses starting with 190.100.0.0/16. The ISP needs to distribute these addresses to three groups of customers. Group 1 has 64 customers, each needing 256 addresses. Group 2 has 128 customers, each needing 128 addresses. Group 3 has 128 customers, each needing 64 addresses. After these allocations, how many addresses are still available in the block?
Subnetting and Supernetting
Hard
A.24576
B.32768
C.40960
D.16384
Correct Answer: 24576
Explanation:
Total addresses in /16 = 65536. Group 1 needs addresses. Group 2 needs addresses. Group 3 needs addresses. Total used = . Available addresses = .
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43Consider a router implementing Random Early Detection (RED) with a minimum threshold () of 20, maximum threshold () of 40, and maximum drop probability () of 0.1. If the average queue length () is 30, and the count of newly arriving packets since the last dropped packet is 5, what is the actual drop probability () for the next arriving packet?
Network assistance Congestion Control Algorithms
Hard
A.0.0526
B.0.05
C.0.1
D.0.0667
Correct Answer: 0.0667
Explanation:
Initial probability . The actual probability .
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44A routing table contains the following entries: 128.96.170.0/23, 128.96.168.0/21, and 128.96.166.0/23. A packet arrives with the destination IP address 128.96.171.92. According to the longest prefix match rule, which entry will be selected?
IP Addressing Both Classfull and Classless
Hard
A.128.96.168.0/21
B.128.96.170.0/23
C.Default route
D.128.96.166.0/23
Correct Answer: 128.96.170.0/23
Explanation:
The binary representation of the third octet of the destination (171) is 10101011. The /23 prefix 128.96.170.0 matches the first 23 bits (170 is 10101010, matching the first 7 bits of 171). The /21 prefix 128.96.168.0 (168 is 10101000) matches the first 5 bits of 171, which means it matches up to 21 bits. The longest match is /23.
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45A TCP connection is operating over a link with a capacity of 10 Mbps and a Round Trip Time (RTT) of 100 ms. The MSS is 1000 bytes. Assuming TCP operates ideally in steady state and uses AIMD, what is the approximate average congestion window size required to fully utilize the link capacity?
TCP Congestion Control
Hard
A.100 segments
B.125 segments
C.1250 segments
D.250 segments
Correct Answer: 125 segments
Explanation:
To fully utilize the link, the throughput must be 10 Mbps. The bandwidth-delay product (BDP) dictates the amount of unacknowledged data needed: . Since MSS is 1000 bytes, the average window size should be segments.
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46An organization requires subnets to support up to 500 hosts each. They are assigned the IP block 172.16.0.0/16. To maximize the number of available subnets while fulfilling the host requirement, what subnet mask should be applied, and how many valid subnets and hosts per subnet will result?
To support 500 hosts, 9 host bits are needed ( hosts). The remaining 32 - 9 = 23 bits form the network prefix (/23). The given block is /16, so bits are used for subnetting, yielding subnets. The subnet mask for /23 is 255.255.254.0.
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47Consider a router with an output link of 2 Mbps and an infinite buffer. Packets arrive according to a Poisson process at an average rate of 1000 packets/sec. Packet lengths are exponentially distributed with an average length of 1000 bits. Using the M/M/1 queuing model, what is the average total delay (waiting time + transmission time) a packet experiences in the router?
Network layer performance
Hard
A.2 ms
B.10 ms
C.0.5 ms
D.1 ms
Correct Answer: 1 ms
Explanation:
Service rate packets/sec. Arrival rate packets/sec. Average total delay seconds = 1 ms.
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48Which of the following IPv6 transition mechanisms encapsulates IPv6 packets within IPv4 packets to allow isolated IPv6 networks to communicate over an IPv4 infrastructure, specifically utilizing protocol type 41 in the IPv4 header?
NETWORK LAYER: IP Addressing
Hard
A.NAT64
B.6to4 Tunneling
C.Dual Stack
D.ISATAP
Correct Answer: 6to4 Tunneling
Explanation:
6to4 Tunneling encapsulates IPv6 packets within IPv4 packets using protocol 41 in the IPv4 header. This enables IPv6 islands to communicate over an IPv4-only network. NAT64 translates addresses, while Dual Stack runs both protocols natively.
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49In the context of the Differentiated Services (DiffServ) architecture, what is the primary function of a traffic conditioner at the boundary of a DiffServ domain?
Network layer services
Hard
A.To compute the shortest path tree for guaranteed bandwidth allocation.
B.To meter, mark, shape, and drop packets to ensure they conform to the Traffic Conditioning Agreement (TCA).
C.To encapsulate packets into MPLS labels based on Per-Hop Behavior (PHB).
D.To assign dynamic port numbers for QoS negotiation.
Correct Answer: To meter, mark, shape, and drop packets to ensure they conform to the Traffic Conditioning Agreement (TCA).
Explanation:
A traffic conditioner at the edge of a DiffServ domain inspects incoming traffic against the Traffic Conditioning Agreement (TCA). It meters the traffic rate, marks packets with appropriate DSCP values, and shapes or drops packets to enforce the agreed-upon profile.
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50In TCP Tahoe, a timeout occurs when the congestion window (cwnd) is at 24 MSS. The ssthresh is updated, and the slow start phase begins. After receiving 4 non-duplicate ACKs in the slow start phase, what will be the value of cwnd?
TCP Congestion Control
Hard
A.5 MSS
B.16 MSS
C.8 MSS
D.4 MSS
Correct Answer: 5 MSS
Explanation:
Upon a timeout, ssthresh is set to MSS, and cwnd drops to 1 MSS. In slow start, cwnd increases by 1 MSS for each ACK received. After 4 ACKs, the cwnd will be MSS.
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51Four Class C networks: 192.168.12.0/24, 192.168.13.0/24, 192.168.14.0/24, and 192.168.15.0/24 are aggregated into a single supernet. What is the supernet mask and the resulting CIDR block?
Subnetting and Supernetting
Hard
A.255.255.252.0; 192.168.14.0/22
B.255.255.248.0; 192.168.8.0/21
C.255.255.254.0; 192.168.12.0/23
D.255.255.252.0; 192.168.12.0/22
Correct Answer: 255.255.252.0; 192.168.12.0/22
Explanation:
The binary representations of the third octet are: 12 (00001100), 13 (00001101), 14 (00001110), and 15 (00001111). The first 6 bits (000011) are common. Thus, 22 bits are common across all addresses. The supernet is 192.168.12.0/22, and the mask is 255.255.252.0.
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52In the context of the Token Bucket algorithm used for traffic shaping, an application generates data at a constant rate of 2 MB/s. The token bucket has a capacity of 1 MB and fills at a rate of 1 MB/s. Assuming the bucket is initially full, what is the maximum duration the application can transmit data at its peak generation rate without being delayed?
Network assistance Congestion Control Algorithms
Hard
A.It can transmit indefinitely
B.2 seconds
C.1 second
D.0.5 seconds
Correct Answer: 1 second
Explanation:
The maximum burst time is given by , where is the bucket capacity, is the maximum transmission rate, and is the token arrival rate. Here, MB, MB/s, and MB/s. So, second.
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53Given the IP address 10.15.25.30 with a subnet mask of 255.224.0.0, determine the network address, the broadcast address, and the total number of valid host IP addresses in this subnet.
The mask 255.224.0.0 is /11. The second octet of the IP (15) in binary is 00001111. The mask in the second octet is 224 (11100000). The bitwise AND yields 0. Thus, the network address is 10.0.0.0. The broadcast address sets the host bits to 1: 00011111 in the second octet gives 31, so 10.31.255.255. Hosts = .
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54In a network using the IPv4 protocol, an IP datagram of length 4500 bytes (including a 20-byte IPv4 header) must traverse a link with an MTU of 1500 bytes. How many fragments will be generated, and what will be the offset value of the final fragment?
Network layer performance
Hard
A.4 fragments, offset = 4440
B.4 fragments, offset = 555
C.3 fragments, offset = 2960
D.3 fragments, offset = 370
Correct Answer: 4 fragments, offset = 555
Explanation:
Data to fragment: bytes. Max data per fragment = MTU - Header = bytes. Since 1480 is a multiple of 8, it can be used. Frag 1: 1480 bytes, offset 0. Frag 2: 1480 bytes, offset . Frag 3: 1480 bytes, offset . Remaining data = bytes. Frag 4: 40 bytes, offset . Total 4 fragments.
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55TCP Fast Recovery is initiated when 3 duplicate ACKs are received. However, if a timeout occurs while the sender is in the Fast Recovery phase, what state transition will the TCP sender make in Reno?
TCP Congestion Control
Hard
A.It will double the cwnd and re-enter Fast Recovery.
B.It will transition directly to the Congestion Avoidance state.
C.It will remain in Fast Recovery until a non-duplicate ACK is received.
D.It will transition to the Slow Start state, resetting cwnd to 1 MSS.
Correct Answer: It will transition to the Slow Start state, resetting cwnd to 1 MSS.
Explanation:
In TCP Reno, a timeout is treated as a severe congestion event. Regardless of the current state (Slow Start, Congestion Avoidance, or Fast Recovery), a timeout causes ssthresh to be set to half the current cwnd, cwnd is reset to 1 MSS, and the sender transitions to the Slow Start state.
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56An IPv4 packet contains an IP options field that specifies Strict Source Routing with 4 IP addresses. Considering standard IP header sizes and padding, what is the total length of the IPv4 header in bytes, and what is the value of the Internet Header Length (IHL) field?
Strict Source Routing option includes a 1-byte code, 1-byte length, 1-byte pointer, and the IP addresses (4 bytes each). Total option length = bytes. Options must be padded to a multiple of 4 bytes, so it requires 1 byte of padding, making options 20 bytes. Base header is 20 bytes. Total header = bytes. IHL indicates the length in 32-bit (4-byte) words: .
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57You are tasked with VLSM (Variable Length Subnet Masking) design for a 192.168.1.0/24 network. Department A needs 120 hosts, Department B needs 60 hosts, and Department C needs 12 hosts. Which of the following represents a valid non-overlapping allocation scheme?
Dept A (120 hosts) needs /25 (126 hosts max), range: 192.168.1.0 - 192.168.1.127. Dept B (60 hosts) needs /26 (62 hosts max), range: 192.168.1.128 - 192.168.1.191. Dept C (12 hosts) needs /28 (14 hosts max), range: 192.168.1.192 - 192.168.1.207. This forms a contiguous, valid, non-overlapping VLSM scheme.
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58In Multiprotocol Label Switching (MPLS), how does a Label Edge Router (LER) determine the Forwarding Equivalence Class (FEC) for an incoming unlabeled IP packet?
Network layer services
Hard
A.By examining the underlying data link layer header to deduce the optimal path.
B.By mapping the packet to a specific FEC based on the IP routing table and assigning a corresponding label before forwarding.
C.By performing a DiffServ code point (DSCP) translation to a fixed label value.
D.By requesting an FEC assignment from the downstream Label Switch Router (LSR) using LDP.
Correct Answer: By mapping the packet to a specific FEC based on the IP routing table and assigning a corresponding label before forwarding.
Explanation:
The Label Edge Router (LER) at the ingress of an MPLS domain inspects the IP header of the incoming unlabeled packet, determines its Forwarding Equivalence Class (FEC) typically by using standard IP routing lookups (longest prefix match, QoS parameters, etc.), pushes the appropriate label(s) onto the packet, and forwards it to the next hop.
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59An end-to-end path consists of three links with available bandwidths of 10 Mbps, 5 Mbps, and 8 Mbps. What is the maximum achievable throughput for a single TCP connection utilizing this path, assuming no cross traffic and that TCP can reach optimal steady-state?
Network layer performance
Hard
A.5 Mbps
B.7.67 Mbps
C.8 Mbps
D.10 Mbps
Correct Answer: 5 Mbps
Explanation:
The maximum achievable throughput for an end-to-end path is constrained by the bottleneck link, which is the link with the lowest bandwidth. In this scenario, the bandwidths are 10 Mbps, 5 Mbps, and 8 Mbps. The bottleneck link is 5 Mbps, so the throughput cannot exceed 5 Mbps.
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60Explicit Congestion Notification (ECN) operates by marking packets instead of dropping them. Which bits in the IP header and the TCP header are utilized to signal and acknowledge ECN-based congestion?
Network assistance Congestion Control Algorithms
Hard
A.IP Header: 3 bits in the Fragment Offset field; TCP Header: URG and PSH flags
B.IP Header: 1 bit in the Flags field; TCP Header: RST and FIN flags
C.IP Header: 2 bits in the Traffic Class field; TCP Header: ECE and CWR flags
D.IP Header: 2 bits in the Options field; TCP Header: SYN and ACK flags
Correct Answer: IP Header: 2 bits in the Traffic Class field; TCP Header: ECE and CWR flags
Explanation:
ECN uses the 2 least significant bits in the Traffic Class field (formerly Type of Service) of the IPv4 or IPv6 header to indicate congestion. In the TCP header, the Explicit Congestion Echo (ECE) flag is used to echo the congestion signal back to the sender, and the Congestion Window Reduced (CWR) flag is used by the sender to acknowledge that it has reacted.