The Network layer is responsible for routing packets from source to destination. A key design issue is the implementation of store-and-forward packet switching, where a router receives a packet completely before forwarding it to the next hop.
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2In the IPv4 header, what is the length of the HLEN (Header Length) field, and what unit does it represent?
A.16 bits, represents bits
B.4 bits, represents 4-byte words
C.8 bits, represents 1-byte words
D.4 bits, represents 8-byte words
Correct Answer: 4 bits, represents 4-byte words
Explanation:
The HLEN field is 4 bits wide. The value indicates the length of the header in 32-bit (4-byte) words. Therefore, the minimum value is 5 ( bytes).
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3Which field in the IPv4 header prevents a packet from circulating indefinitely in a network with routing loops?
A.Fragment Offset
B.Time to Live (TTL)
C.Header Checksum
D.Type of Service
Correct Answer: Time to Live (TTL)
Explanation:
The Time to Live (TTL) field is decremented by 1 at each hop (router). When the TTL reaches 0, the packet is discarded, preventing infinite looping.
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4Identify the Class of the IPv4 address: 191.255.254.1.
A.Class A
B.Class B
C.Class D
D.Class C
Correct Answer: Class B
Explanation:
The first octet range for Class B is 128 to 191. Since the first octet is 191, this is a Class B address.
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5What is the default subnet mask for a Class C IP address?
A.255.255.0.0
B.255.255.255.0
C.255.255.255.255
D.255.0.0.0
Correct Answer: 255.255.255.0
Explanation:
Class C networks use the first three octets for the network part and the last octet for the host part, resulting in a default mask of 255.255.255.0 (/24).
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6In Classless Inter-Domain Routing (CIDR), what does the suffix /21 indicate in the address block 192.168.0.0/21?
A.21 hosts are available
B.The network mask is 21 bits long
C.The host ID is 21 bits long
D.There are 21 subnets
Correct Answer: The network mask is 21 bits long
Explanation:
The slash notation (CIDR notation) indicates the number of bits used for the network prefix (Network ID). /21 means the first 21 bits identify the network.
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7Calculate the number of usable hosts in a subnet with the mask 255.255.255.224.
A.64
B.62
C.30
D.32
Correct Answer: 30
Explanation:
255.255.255.224 corresponds to a /27 mask ( bits network, 5 bits host). The number of total addresses is . Usable hosts = (subtracting network and broadcast addresses).
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8Which field in the IP header is used to reassemble fragmented packets?
A.TTL and Protocol
B.Identification, Flags, and Fragment Offset
C.TOS and HLEN
D.Source IP and Destination IP
Correct Answer: Identification, Flags, and Fragment Offset
Explanation:
Fragmentation relies on the Identification (to group fragments of the same packet), Flags (to indicate more fragments), and Fragment Offset (to order the fragments).
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9What is the maximum size of an IPv4 packet (including header and data)?
A. bytes
B.4096 bytes
C.1500 bytes
D.65,535 bytes
Correct Answer: 65,535 bytes
Explanation:
The Total Length field in the IPv4 header is 16 bits wide. Therefore, the maximum length is bytes.
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10If an IP address is 200.10.20.5 and the subnet mask is 255.255.255.240, what is the Subnet Address (Network ID)?
A.200.10.20.5
B.200.10.20.4
C.200.10.20.0
D.200.10.20.16
Correct Answer: 200.10.20.0
Explanation:
Mask 240 is 11110000 in binary. The last octet of IP is 5 (00000101). Performing bitwise AND: 00000101 AND 11110000 = 00000000 (0). So the subnet ID is 200.10.20.0.
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11Which of the following is a private IP address range defined by RFC 1918?
A.172.16.0.0 to 172.31.255.255
B.169.254.0.0 to 169.254.255.255
C.224.0.0.0 to 239.255.255.255
D.11.0.0.0 to 11.255.255.255
Correct Answer: 172.16.0.0 to 172.31.255.255
Explanation:
The private IP ranges are 10.0.0.0/8, 172.16.0.0/12 (172.16.0.0–172.31.255.255), and 192.168.0.0/16.
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12In IPv6, how many bits long is the address?
A.32 bits
B.128 bits
C.64 bits
D.256 bits
Correct Answer: 128 bits
Explanation:
IPv6 uses 128-bit addresses, usually represented as eight groups of four hexadecimal digits.
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13What is Supernetting predominantly used for?
A.Encrypting IP headers
B.Route aggregation to reduce routing table size
C.Dividing a network into smaller sub-networks
D.Assigning dynamic IP addresses
Correct Answer: Route aggregation to reduce routing table size
Explanation:
Supernetting (CIDR aggregation) combines multiple contiguous smaller networks into a larger network entry, reducing the number of entries in global routing tables.
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14Given the IP address block 192.168.1.0/24, if you need to create 4 subnets, how many bits must be borrowed from the host portion?
A.2 bits
B.1 bit
C.4 bits
D.3 bits
Correct Answer: 2 bits
Explanation:
To create 4 subnets, you need , where is the number of bits borrowed. . Thus, 2 bits are needed.
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15Which of the following represents the loopback address in IPv4?
A.127.0.0.0/8
B.255.255.255.255
C.0.0.0.0
D.192.168.0.1
Correct Answer: 127.0.0.0/8
Explanation:
The entire 127.0.0.0/8 block is reserved for loopback purposes, with 127.0.0.1 being the most commonly used address to test the local TCP/IP stack.
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16The Fragment Offset value in the IP header is measured in units of:
A.4 bytes
B.8 bytes
C.1 byte
D.16 bytes
Correct Answer: 8 bytes
Explanation:
The 13-bit fragment offset field counts data in 8-byte blocks. This allows the offset to map to the maximum packet size.
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17In a Class B network, what is the maximum number of hosts per network?
A.254
B.
C.
D.
Correct Answer:
Explanation:
A Class B address has 16 bits for the Network ID and 16 bits for the Host ID. The number of hosts is (65,534).
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18Which IPv6 address type identifies a set of interfaces where a packet is delivered to the nearest one?
A.Anycast
B.Multicast
C.Broadcast
D.Unicast
Correct Answer: Anycast
Explanation:
Anycast addresses are assigned to a group of interfaces (usually on different nodes). A packet sent to an anycast address is delivered to the 'nearest' interface according to routing protocols.
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19What is the result of the bitwise AND operation between IP address 192.168.10.150 and subnet mask 255.255.255.192?
A.192.168.10.64
B.192.168.10.128
C.192.168.10.0
D.192.168.10.192
Correct Answer: 192.168.10.128
Explanation:
Last octet calculation: 150 (10010110) AND 192 (11000000) = 10000000 (128). The result is 192.168.10.128.
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20The Protocol field in the IP header indicates:
A.The higher-level protocol (e.g., TCP, UDP) using the IP layer
B.The type of physical network used
C.The priority of the packet
D.The version of IP protocol
Correct Answer: The higher-level protocol (e.g., TCP, UDP) using the IP layer
Explanation:
The Protocol field identifies the payload protocol. For example, 6 indicates TCP, 17 indicates UDP, and 1 indicates ICMP.
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21In the IPv6 header, which field replaces the TTL (Time To Live) field found in IPv4?
A.Traffic Class
B.Next Header
C.Hop Limit
D.Flow Label
Correct Answer: Hop Limit
Explanation:
IPv6 renamed the TTL field to Hop Limit to more accurately reflect its function (counting hops rather than seconds).
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22Which of the following statements about Connectionless Service in the Network Layer is TRUE?
A.Resources are reserved in advance
B.Packets are treated independently and may take different routes
C.It guarantees in-order delivery
D.Packets are called virtual circuits
Correct Answer: Packets are treated independently and may take different routes
Explanation:
In a connectionless (datagram) service, each packet is routed independently based on the destination address, potentially arriving out of order.
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23Find the Broadcast address for the subnet 10.1.1.0/28.
A.10.1.1.15
B.10.1.1.14
C.10.1.1.16
D.10.1.1.255
Correct Answer: 10.1.1.15
Explanation:
/28 means block size is . The subnet is 10.1.1.0 to 10.1.1.15. The last address (10.1.1.15) is the broadcast address.
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24Which IP Class is reserved for Multicasting?
A.Class B
B.Class D
C.Class C
D.Class E
Correct Answer: Class D
Explanation:
Class D addresses (224.0.0.0 to 239.255.255.255) are reserved for Multicasting.
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25Forwarding in the network layer is primarily the process of:
A.Assigning IP addresses to hosts
B.Calculating the shortest path
C.Creating the routing table
D.Moving a packet from an input interface to an appropriate output interface
Correct Answer: Moving a packet from an input interface to an appropriate output interface
Explanation:
Forwarding is the local action of moving a packet from an input link to the appropriate output link within a router, based on the routing table.
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26What is the simplified hexadecimal representation of the IPv6 address 2001:0DB8:0000:0000:0000:0000:1428:57ab?
A.2001:DB8:1428:57ab
B.2001:DB8:0:0:0:0:1428:57ab
C.2001:DB8::0::1428:57ab
D.2001:DB8::1428:57ab
Correct Answer: 2001:DB8::1428:57ab
Explanation:
Leading zeros can be omitted, and a single contiguous string of zero blocks can be replaced by ::. Thus, 0000:0000:0000:0000 becomes ::.
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27A subnet mask of /30 is typically used for:
A.Point-to-point links between two routers
B.Class A networks
C.Loopback interfaces
D.Large enterprise networks
Correct Answer: Point-to-point links between two routers
Explanation:
A /30 mask provides only 2 usable host addresses (), which is exactly enough for a point-to-point link connecting two routers.
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28Which mechanism allows a router to group multiple small CIDR blocks into one larger routing entry?
A.Route Aggregation (Supernetting)
B.Subnetting
C.Tunneling
D.Fragmentation
Correct Answer: Route Aggregation (Supernetting)
Explanation:
Route Aggregation (or Supernetting) allows a router to advertise a single shorter prefix (e.g., /20) that covers multiple longer prefixes (e.g., several /24s), reducing routing table size.
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29If the More Fragments (MF) bit is set to 0 and the Fragment Offset is non-zero, what does this indicate?
A.The packet has been dropped
B.This is the first fragment
C.This is the last fragment of the original packet
D.The packet is not fragmented
Correct Answer: This is the last fragment of the original packet
Explanation:
MF=0 means no more fragments follow. If Offset > 0, it means there were preceding fragments. Therefore, this is the last fragment.
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30In Classful addressing, which class range is 240.0.0.0 to 255.255.255.254?
A.Class D
B.Class C
C.Class E
D.Class F
Correct Answer: Class E
Explanation:
Class E (240.0.0.0 to 255.255.255.255) is reserved for experimental/research purposes.
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31What is the Longest Prefix Match rule?
A.The router matches the source IP instead of destination IP
B.The router forwards the packet based on the routing table entry with the longest matching network mask
C.The router selects the route with the fewest hops
D.The router selects the path with the highest bandwidth
Correct Answer: The router forwards the packet based on the routing table entry with the longest matching network mask
Explanation:
When looking up a destination IP in the routing table, if multiple entries match, the router uses the entry with the most specific (longest) network prefix (mask).
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32Which of the following headers is NOT present in IPv6 but was present in IPv4?
A.Destination Address
B.Header Checksum
C.Source Address
D.Hop Limit (TTL)
Correct Answer: Header Checksum
Explanation:
IPv6 removed the Header Checksum to improve processing speed, relying on Layer 2 and Layer 4 checksums for error detection.
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33Calculate the first valid host address for the network 192.168.5.0/26.
A.192.168.5.0
B.192.168.5.1
C.192.168.5.63
D.192.168.5.64
Correct Answer: 192.168.5.1
Explanation:
The network address is 192.168.5.0. The first usable host is Network ID + 1, which is 192.168.5.1.
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34What happens if a router receives a packet larger than the Maximum Transmission Unit (MTU) of the outgoing link, and the DF (Don't Fragment) flag is set to 1?
A.The router buffers the packet until the link is clear
B.The router truncates the data
C.The router discards the packet and sends an ICMP error message to the source
D.The router fragments the packet anyway
Correct Answer: The router discards the packet and sends an ICMP error message to the source
Explanation:
If DF=1, fragmentation is forbidden. The router must drop the packet and typically sends an ICMP 'Fragmentation Needed' message back to the sender.
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35An organization is assigned the block 200.200.200.0/24. They need to create subnets that support at least 20 hosts each. What is the most efficient subnet mask to use?
A./25
B./27
C./26
D./28
Correct Answer: /27
Explanation:
To support 20 hosts, we need 5 host bits ( hosts). A /28 only supports hosts. A /27 leaves 5 bits for hosts. So /27 is the correct choice.
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36Which field in the IPv4 header is used for Quality of Service (QoS) or Differentiated Services?
A.Protocol
B.Type of Service (ToS) / Differentiated Services (DiffServ)
C.Padding
D.Flags
Correct Answer: Type of Service (ToS) / Differentiated Services (DiffServ)
Explanation:
The 8-bit TOS field (redefined as Differentiated Services) allows prioritization of packets based on network requirements (throughput, delay, reliability).
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37How does the IPv6 header handle options?
A.Appended to the data payload
B.IPv6 does not support options
C.Using Extension Headers inserted between the IPv6 header and the upper-layer header
D.Included in the fixed 40-byte header
Correct Answer: Using Extension Headers inserted between the IPv6 header and the upper-layer header
Explanation:
IPv6 uses a fixed main header. Additional functionalities (fragmentation, routing options, security) are handled via 'Next Header' pointers chaining to Extension Headers.
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38If a host has the IP 172.16.45.14 and mask 255.255.255.252, what is the Broadcast address?
A.172.16.45.15
B.172.16.45.12
C.172.16.45.255
D.172.16.45.14
Correct Answer: 172.16.45.15
Explanation:
Mask 252 (11111100) has a block size of 4. Ranges: 0-3, 4-7, 8-11, 12-15. IP 14 falls in the 12-15 range. Network: .12, Broadcast: .15.
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39What is the primary motivation for the transition from IPv4 to IPv6?
A.Faster routing speeds
B.Better encryption standards
C.Address space exhaustion in IPv4
D.Smaller header size
Correct Answer: Address space exhaustion in IPv4
Explanation:
While IPv6 offers other improvements, the primary driver was the depletion of the approximately 4.3 billion IPv4 addresses.
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40Which component of network layer performance is defined as the number of packets passing through the network per unit of time?
A.Throughput
B.Packet Loss
C.Delay
D.Jitter
Correct Answer: Throughput
Explanation:
Throughput measures the actual rate at which data is successfully transferred through the network.
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41In the context of IPv4, what is the 'Loopback' functionality used for?
A.Creating a routing loop
B.Routing packets back to the source if an error occurs
C.Testing the network interface card and protocol stack software without sending packets on the network
D.Sending data to all hosts on the subnet
Correct Answer: Testing the network interface card and protocol stack software without sending packets on the network
Explanation:
Addresses in 127.0.0.0/8 allow a host to send packets to itself to verify that the internal TCP/IP stack is functioning correctly.
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42Given 4 Class C networks: 200.1.0.0, 200.1.1.0, 200.1.2.0, and 200.1.3.0. What is the supernet (aggregated) address?
A.200.1.0.0/22
B.200.1.0.0/24
C.200.1.0.0/23
D.200.1.0.0/21
Correct Answer: 200.1.0.0/22
Explanation:
The third octets are 0 (00000000), 1 (00000001), 2 (00000010), 3 (00000011). The first 6 bits of the third octet are common. Class C is /24. Aggregating 4 blocks () means decreasing mask by 2 bits. . Supernet: 200.1.0.0/22.
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43What is the binary equivalent of the subnet mask 255.255.248.0?
248 in binary is 11111000. The first two octets are all 1s. The last is all 0s.
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44In IPv6, the Flow Label field is used to:
A.Calculate checksums
B.Limit the number of hops
C.Identify the next header type
D.Identify packets belonging to a specific sequence requiring special handling (e.g., real-time audio/video)
Correct Answer: Identify packets belonging to a specific sequence requiring special handling (e.g., real-time audio/video)
Explanation:
The Flow Label is a 20-bit field used to tag sequences of packets (flows) so that routers can treat them efficiently without deep packet inspection.
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45Which protocol is responsible for mapping an IP address to a physical MAC address?
A.ICMP
B.DHCP
C.ARP
D.RARP
Correct Answer: ARP
Explanation:
The Address Resolution Protocol (ARP) translates a known IP address (Network Layer) into a physical MAC address (Data Link Layer).
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46A network administrator wants to subnet the network 172.16.0.0/16 into 100 subnets. What is the new subnet mask?
A./23
B./22
C./21
D./25
Correct Answer: /23
Explanation:
We need 100 subnets. . , . We need 7 bits for the subnet. Original mask is /16. New mask = .
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47Which of the following is TRUE regarding IPv6 fragmentation?
A.Only the source node can fragment packets
B.Destination nodes reassemble and re-fragment packets
C.Fragmentation is not supported in IPv6
D.Routers perform fragmentation when the packet is too large
Correct Answer: Only the source node can fragment packets
Explanation:
In IPv6, routers do not fragment packets to improve performance. The source must perform Path MTU Discovery and fragment the packet before sending if necessary.
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48What is the purpose of the Padding field in the IPv4 header?
A.To increase the packet size to the minimum Ethernet frame size
B.To add security to the packet
C.To ensure the header ends on a 32-bit boundary
D.To store routing options
Correct Answer: To ensure the header ends on a 32-bit boundary
Explanation:
The IPv4 header length (HLEN) is measured in 4-byte words. If the options field is not a multiple of 32 bits, padding (zeros) is added to align the header.
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49Which value in the first byte of an IP address indicates a Class A address?
A.224 - 239
B.128 - 191
C.192 - 223
D.0 - 127
Correct Answer: 0 - 127
Explanation:
Class A addresses have the first bit set to 0, resulting in a range of 0 to 127 in the first octet.
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50If you have a /22 prefix, what is the block size (number of IP addresses) in that subnet?
A.2048
B.1024
C.256
D.512
Correct Answer: 1024
Explanation:
A /22 mask leaves bits for the host portion. The total number of addresses is .