Network Layer

Question 31

Suppose that the maximum transmit window size for a TCP connection is 12000 bytes. Each packet consists of 2000 bytes. At some point of time, the connection is in slow-start phase with a current transmit window of 4000 bytes. Subsequently, the transmitter receives two acknowledgements. Assume that no packets are lost and there are no time-outs. What is the maximum possible value of the current transmit window?

• 4000 bytes
• 8000 bytes
• 10000 bytes
• 12000 bytes

Question 32

Traceroute reports a possible route that is taken by packets moving from some host A to some other host B. Which of the following options represents the technique used by traceroute to identify these hosts  

• By progressively querying routers about the next router on the path to B using ICMP packets, starting with the first router
• By requiring each router to append the address to the ICMP packet as it is forwarded to B. The list of all routers en-route to B is returned by B in an ICMP reply packet
• By ensuring that an ICMP reply packet is returned to A by each router en-route to B, in the ascending order of their hop distance from A
• By locally computing the shortest path from A to B

Question 33

Count to infinity is a problem associated with

• link state routing protocol.
• distance vector routing protocol
• DNS while resolving host name.
• TCP for congestion control.

Question 34

In a communication network, a packet of length L bits takes link L1 with a probability of p₁or link L2 with a probability of p₂. Link L1 and L2 have bit error probability of b₁ and b₂respectively. The probability that the packet will be received without error via either L1 or L2 is  

• (1 - b1)Lp1 + (1 - b2)Lp2

• [1 - (b1 + b2)L]p1p2

• (1 - b1)L (1 - b2)Lp1p2

• 1 - (b1Lp1 + b2Lp2)

Question 35

A company has a class C network address of 204.204.204.0. It wishes to have three subnets, one with 100 hosts and two with 50 hosts each. Which one of the following options represents a feasible set of subnet address/subnet mask pairs?  

• 204.204.204.128/255.255.255.192 204.204.204.0/255.255.255.128 204.204.204.64/255.255.255.128
• 204.204.204.0/255.255.255.192 204.204.204.192/255.255.255.128 204.204.204.64/255.255.255.128
• 204.204.204.128/255.255.255.128 204.204.204.192/255.255.255.192 204.204.204.224/255.255.255.192
• 204.204.204.128/255.255.255.128 204.204.204.64/255.255.255.192 204.204.204.0/255.255.255.192

Question 36

Assume that "host1.mydomain.dom" has an IP address of 145.128.16.8. Which of the following options would be most appropriate as a subsequence of steps in performing the reverse lookup of 145.128.16.8? In the following options "NS" is an abbreviation of "nameserver".

• Query a NS for the root domain and then NS for the "dom" domains
• Directly query a NS for "dom" and then a NS for "mydomain.dom" domains
• Query a NS for in-addr.arpa and then a NS for 128.145.in-addr.arpa domains
• Directly query a NS for 145.in-addr.arpa and then a NS for 128.145.in-addr.arpa domains

Question 37

An IP datagram of size 1000 bytes arrives at a router. The router has to forward this packet on a link whose MTU (maximum transmission unit) is 100 bytes. Assume that the size of the IP header is 20 bytes. The number of fragments that the IP datagram will be divided into for transmission is :   Note : This question was asked as Numerical Answer Type.

• 10
• 50
• 12
• 13

Question 38

Which of the following statements is TRUE?  

• Both Ethernet frame and IP packet include checksum fields
• Ethernet frame includes a checksum field and IP packet includes a CRC field
• Ethernet frame includes a CRC field and IP packet includes a checksum field
• Both Ethernet frame and IP packet include CRC fields

Question 39

Two popular routing algorithms are Distance Vector(DV) and Link State (LS) routing. Which of the following are true?
(S1) Count to infinity is a problem only with DV and not LS routing
(S2) In LS, the shortest path algorithm is run only at one node
(S3) In DV, the shortest path algorithm is run only at one node
(S4) DV requires lesser number of network messages than LS

• S1, S2 and S4 only
• S1, S3 and S4 only
• S2 and S3 only
• S1 and S4 only

Question 40

Which of the following option is false regarding option field in the IPv4 header:

• The Value of "Type" in the Security option field of an IPv4 header is 131.
• If the header length is greater than 5 (i.e., it is from 6 to 15) it means that the options field is present and must be considered.
• Copied, Option Class, and Option Number are sometimes referred to as a single eight-bit field, the Option Type.
• None of these