Network Layer

Question 1

If a Company require 60 hosts then What is the best possible subnet mask?

• 255.255.255.0
• 255.255.255.192
• 255.255.225.224
• 225.225.255.240

Question 2

In class C , if subnet mask is 255.255.255.224 then calculates number of subnet?

• 6
• 8
• 4
• None of the Above

Question 3

In an IPv4 datagram, the M bit is 0, the value of HLEN is 10, the value of total length is 400 and the fragment offset value is 300. The position of the datagram, the sequence numbers of the first and the last bytes of the payload, respectively are

• Last fragment, 2400 and 2789
• First fragment, 2400 and 2759
• Last fragment, 2400 and 2759
• Middle fragment, 300 and 689

Question 4

Consider the same data as given in previous question. After the update in the previous question, the link N1-N2 goes down. N2 will reflect this change immediately in its distance vector as cost, infinite. After the NEXT ROUND of update, what will be cost to N1 in the distance vector of N3?

• 3
• 9
• 10
• Infinite

Question 5

One of the header fields in an IP datagram is the Time to Live(TTL)field.Which of the following statements best explains the need for this field?

• It can be used to prioritize packets
• It can be used to reduce delays
• It can be used to optimize throughput
• It can be used to prevent packet looping

Question 6

Consider a network with 6 routers R1 to R6 connected with links having weights as shown in the following diagram:

All the routers use the distance vector based routing algorithm to update their routing tables. Each router starts with its routing table initialized to contain an entry for each neighbour with the weight of the respective connecting link. After all the routing tables stabilize, how many links in the network will never be used for carrying any data?

• 4

• 3

• 2

• 1

Question 7

For which one of the following reasons does Internet Protocol (IP) use the timeto- live (TTL) field in the IP datagram header

• Ensure packets reach destination within that time

• Discard packets that reach later than that time

• Prevent packets from looping indefinitely

• Limit the time for which a packet gets queued in intermediate routers.

Question 8

Consider the following three statements about link state and distance vector routing protocols, for a large network with 500 network nodes and 4000 links.

[S1] The computational overhead in link state protocols 
     is higher than in distance vector protocols.
[S2] A distance vector protocol (with split horizon) 
     avoids persistent routing loops, but not a link
     state protocol.
[S3] After a topology change, a link state protocol 
     will converge faster than a distance vector
     protocol.

Which one of the following is correct about S1, S2, and S3 ?

• S1, S2, and S3 are all true.
• S1, S2, and S3 are all false.
• S1 and S2 are true, but S3 is false
• S1 and S3 are true, but S2 is false

Question 9

Which one of the following is TRUE about interior Gateway routing protocols - Routing Information Protocol (RIP) and Open Shortest Path First (OSPF)

• RIP uses distance vector routing and OSPF uses link state routing
• OSPF uses distance vector routing and RIP uses link state routing
• Both RIP and OSPF use link state routing
• Both RIP and OSPF use distance vector routing

Question 10

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?

• Only I1 and I2
• Only I1
• Only I2 and I3
• Only I3 and I4