A directory of Objective Type Questions covering all the Computer Science subjects. Here you can access and discuss Multiple choice questions and answers for various compitative exams and interviews.

41. An IP machine Q has a path to another IP machine H via three IP routers R1, R2, and R3.

Q—R1—R2—R3—H

H acts as an HTTP server, and Q connects to H via HTTP and downloads a file. Session layer encryption is used, with DES as the shared key encryption protocol. Consider the following four pieces of information:

[I1] The URL of the file downloaded by Q
[I2] The TCP port numbers at Q and H
[I3] The IP addresses of Q and H
[I4] The link layer addresses of Q and H

Which of I1, I2, I3, and I4 can an intruder learn through sniffing at R2 alone?
a. Only I1 and I2
b. Only I1
c. Only I2 and I3
d. Only I3 and I4
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Answer: (c).Only I2 and I3

42. Host A (on TCP/IP v4 network A) sends an IP datagram D to host B (also on TCP/IP v4 network B). Assume that no error occurred during the transmission of D. When D reaches B, which of the following IP header field(s) may be different from that of the original datagram D?

(i) TTL
(ii) Checksum
(iii) Fragment Offset
a. (i) only
b. (i) and (ii) only
c. (ii) and (iii) only
d. (i), (ii) and (iii)
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Answer: (d).(i), (ii) and (iii)

43. Classless Inter-domain Routing (CIDR) receives a packet with address 131.23.151.76. The router’s routing table has the following entries:

Prefix Output Interface Identifier
131.16.0.0/12 3
131.28.0.0/14 5
131.19.0.0/16 2
131.22.0.0/15 1

The identifier of the output interface on which this packet will be forwarded is ______.
a. 1
b. 2
c. 3
d. 5
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Answer: (a).1

44. Every host in an IPv4 network has a 1-second resolution real-time clock with battery backup. Each host needs to generate up to 1000 unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a 50-bit globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around?
a. 128
b. 64
c. 256
d. 512
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Answer: (c).256

45. An IP router with a Maximum Transmission Unit (MTU) of 1500 bytes has received an IP packet of size 4404 bytes with an IP header of length 20 bytes. The values of the relevant fields in the header of the third IP fragment generated by the router for this packet are
a. MF bit: 0, Datagram Length: 1444; Offset: 370
b. MF bit: 1, Datagram Length: 1424; Offset: 185
c. MF bit: 1, Datagram Length: 1500; Offset: 37
d. MF bit: 0, Datagram Length: 1424; Offset: 2960
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Answer: (a).MF bit: 0, Datagram Length: 1444; Offset: 370

46. Two computers C1 and C2 are configured as follows. C1 has IP address 203.197.2.53 and netmask 255.255.128.0. C2 has IP address 203.197.75.201 and netmask 255.255.192.0. which one of the following statements is true?
a. C1 and C2 both assume they are on the same network
b. C2 assumes C1 is on same network, but C1 assumes C2 is on a different network
c. C1 assumes C2 is on same network, but C2 assumes C1 is on a different network
d. C1 and C2 both assume they are on different networks
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Answer: (c).C1 assumes C2 is on same network, but C2 assumes C1 is on a different network

47. Station A needs to send a message consisting of 9 packets to Station B using a sliding window (window size 3) and go-back-n error control strategy. All packets are ready and immediately available for transmission. If every 5th packet that A transmits gets lost (but no acks from B ever get lost), then what is the number of packets that A will transmit for sending the message to B?
a. 12
b. 14
c. 16
d. 18
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Answer: (c).16

48. The address resolution protocol (ARP) is used for
a. Finding the IP address from the DNS
b. Finding the IP address of the default gateway
c. Finding the IP address that corresponds to a MAC address
d. Finding the MAC address that corresponds to an IP address
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Answer: (d).Finding the MAC address that corresponds to an IP address

49. In a packet switching network, packets are routed from source to destination along a single path having two intermediate nodes. If the message size is 24 bytes and each packet contains a header of 3 bytes, then the optimum packet size is:
a. 4
b. 6
c. 7
d. 9
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Answer: (d).9

50. The routing table of a router is shown below:

Destination Sub net mask Interface
128.75.43.0 255.255.255.0 Eth0
128.75.43.0 255.255.255.128 Eth1
192.12.17.5 255.255.255.255 Eth3
default Eth2

On which interfaces will the router forward packets addressed to destinations 128.75.43.16 and 192.12.17.10 respectively?
a. Eth1 and Eth2
b. Eth0 and Eth2
c. Eth0 and Eth3
d. Eth1 and Eth3
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Answer: (a).Eth1 and Eth2

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