Data Communication and Computer Networks MCQ - Functions of OSI and TCP/IP Layers

46 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?

Statement S1
The Distance Vector routing protocols rely on the information from their directly connected neighbours in order to calculate and accumulate route information. Distance Vector routing protocols require very little overhead as compared to Link State routing protocols as measured by memory and processor power while the Link State routing protocols do not rely solely on the information from the neighbours or adjacent router in order to calculate route information. I nstead, Link State routing protocols have a system of databases that they use in order to calculate the best route to destinations in the network. This is TRUE
Statement S3
Distance Vector exchanges the routing updates periodically whether the topology is change or not, this will maximize the convergence time which increases the chance of routing loops while the Link State routing protocols send triggered change based updates when there is a topology change. After initial flood, pass small event based triggered link state updates to all other routers. This will minimize the convergence time that’s why there is no chance of routing loops. This is TRUE.

47 Assume that source S and destination D are connected through two intermediate routers labels R. Determine how many times each packet has to visit the network layer and the data link layer during a transmission form S to D.

Assume the source S & destination D are connected through two intermediate routers labled R. Determine how many times each packet has to visit the network layer and data link layer during a transmission from S to D.

Network Layer 4 times
Data link layer 6 times

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

We know that RIP uses distance vector routing and QSPF uses link state routing.

49 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?

Since, the router R₁ contains TCP part numbers of Q and R₂ contains the TCP part numbers of H at Data link layer, and with both routers contains IP addresses of Q and H at Network layer. So, only statement I₂ and I₃ will be true.

50 Consider an IP packet with a length of 4500 bytes that includes a 20-byte IPv4 header and a 40-byte TCP header. The packet is forwarded to an IPv4 router that supports a Maximum Transmission Unit (MTU) of 600 bytes. Assume that the length of the IP header in all the outgoing fragments of this packet is 20 bytes. Assume that the fragmentation offset value stored in the first fragment is 0.
The fragmentation offset value stored in the third fragment is ________.