71. Host X has IP address and is connected through two routers R1 and R2 to an­other host Y with IP address Router R1 has IP addresses and R2 has IP addresses and The netmask used in the network is

Given the information above, how many distinct subnets are guaranteed to already exist in the network?
a. 1
b. 2
c. 3
d. 6
Answer: (c).3

72. The transport layer protocols used for real time multimedia, file transfer, DNS and email, respectively are:
a. TCP, UDP, UDP and TCP
b. UDP, TCP, TCP and UDP
c. UDP, TCP, UDP and TCP
d. TCP, UDP, TCP and UDP
Answer: (c).UDP, TCP, UDP and TCP

73. Which of the following transport layer protocols is used to support electronic mail?
b. IP
c. TCP
d. UDP
Answer: (c).TCP

74. Consider an instance of TCP’s Additive Increase Multiplicative Decrease (AIMD) algorithm where the window size at the start of the slow start phase is 2 MSS and the threshold at the start of the first transmission is 8 MSS. Assume that a timeout occurs during the fifth transmission. Find the congestion window size at the end of the tenth transmission.
a. 8 MSS
b. 14 MSS
c. 7 MSS
d. 12 MSS
Answer: (c).7 MSS

75. A layer-4 firewall (a device that can look at all protocol headers up to the transport layer) CANNOT
a. block entire HTTP traffic during 9:00PM and 5 :0OAM
b. block all ICMP traffic
c. stop incoming traffic from a specific IP address but allow outgoing traffic to the same IP address
d. block TCP traffic from a specific user on a multi-user system during 9:00PM and 5:00AM
Answer: (d).block TCP traffic from a specific user on a multi-user system during 9:00PM and 5:00AM

76. While opening a TCP connection, the initial sequence number is to be derived using a time-of-day(ToD) clock that keeps running even when the host is down. The low order 32 bits of the counter of the ToD clock is to be used for the initial sequence numbers. The clock counter increments once per millisecond. The maximum packet lifetime is given to be 64s. Which one of the choices given below is closest to the minimum permissible rate at which sequence numbers used for packets of a connection can increase?
a. 0.015/s
b. 0.064/s
c. 0.135/s
d. 0.327/s
Answer: (a).0.015/s

77. Which of the following system calls results in the sending of SYN packets?
a. socket
b. bind
c. listen
d. connect
Answer: (d).connect

78. In the slow start phase of the TCP congestion control algorithm, the size of the congestion window
a. does not increase
b. increases linearly
c. increases quadratically
d. increases exponentially
Answer: (d).increases exponentially

79. Which one of the following uses UDP as the transport protocol?
b. Telnet
c. DNS
Answer: (c).DNS

80. Let the size of congestion window of a TCP connection be 32 KB when a timeout occurs. The round trip time of the connection is 100 msec and the maximum segment size used is 2 KB. The time taken (in msec) by the TCP connection to get back to 32 KB congestion window is _________.
a. 1100 to 1300
b. 800 to 1000
c. 1400 to 1600
d. 1500 to 1700
Answer: (a).1100 to 1300