# Network Layer Protocol

 Question 1
Consider a network with three routers P, Q, R shown in the figure below. All the links have cost of unity.

The routers exchange distance vector routing information and have converged on the routing tables, after which the link Q-R fails. Assume that P and Q send out routing updates at random times, each at the same average rate. The probability of a routing loop formation (rounded off to one decimal place) between P and Q, leading to count-to-infinity problem, is ____
 A 0.25 B 0.33 C 0.5 D 0.75
GATE CSE 2022   Computer Network
Question 1 Explanation:
 Question 2
Consider routing table of an organization's router shown below:
$\begin{array}{|l|l|l|} Subnet Number & Subnet Mask & Next Hop \\ 12.20.164.0 & 255.255.252.0 & R1 \\ 12.20.170.0 & 255.255.254.0 & R2 \\ 12.20.168.0 & 255.255.254.0 & Interface 0 \\ 12.20.166.0 & 255.255.254.0 & Interface 1 \\ default & ~ & R3 \\ \hline \end{array}$
Which of the following prefixes in CIDR notation can be collectively used to correctly aggregate all of the subnets in the routing table?
MSQ
 A 12.20.164.0/20 B 12.20.164.0/22 C 12.20.164.0/21 D 12.20.168.0/22
GATE CSE 2022   Computer Network
Question 2 Explanation:
 Question 3
Consider an enterprise network with two Ethernet segments, a web server and a firewall, connected via three routers as shown below.

What is the number of subnets inside the enterprise network?
 A 3 B 12 C 6 D 8
GATE CSE 2022   Computer Network
Question 3 Explanation:
 Question 4
Consider a computer network using the distance vector routing algorithm in its network layer. The partial topology of the network is shown below.

The objective is to find the shortest-cost path from the router R to routers P and Q. Assume that R does not initially know the shortest routes to P and Q. Assume that R has three neighboring routers denoted as X, Y and Z. During one iteration, R measures its distance to its neighbors X, Y, and Z as 3, 2 and 5, respectively. Router R gets routing vectors from its neighbors that indicate that the distance to router P from routers X, Y and Z are 7, 6 and 5, respectively. The routing vector also indicates that the distance to router Q from routers X, Y and Z are 4, 6 and 8 respectively. Which of the following statement(s) is/are correct with respect to the new routing table o R, after updation during this iteration?
[MSQ]
 A The distance from R to P will be stored as 10 B The distance from R to Q will be stored as 7 C The next hop router for a packet from R to P is Y D The next hop router for a packet from R to Q is Z
GATE CSE 2021 SET-2   Computer Network
Question 4 Explanation:
 Question 5
Which of the following classes of languages can validate an IPv4 address in dotted decimal format?
It is to be ensured that the decimal values lie between 0 and 255.
 A RE and higher B CFG and higher C CSG and higher D Recursively enumerable language
ISRO CSE 2020   Computer Network
Question 5 Explanation:
 Question 6
An organization requires a range of IP address to assign one to each of its 1500 computers. The organization has approached an Internet Service Provider (ISP) for this task. The ISP uses CIDR and serves the requests from the available IP address space 202.61.0.0/17. The ISP wants to assign an address space to the organization which will minimize the number of routing entries in the ISP?s router using route aggregation. Which of the following address spaces are potential candidates from which the ISP can allot any one of the organization?

I. 202.61.84.0/21
II. 202.61.104.0/21
III. 202.61.64.0/21
IV. 202.61.144.0/21
 A I and II only B II and III only C III and IV only D I and IV only
GATE CSE 2020   Computer Network
Question 6 Explanation:
 Question 7
onsider the following statements about the functionality of an IP based router.

I. A router does not modify the IP packets during forwarding.
II. It is not necessary for a router to implement any routing protocol.
III. A router should reassemble IP fragments if the MTU of the outgoing link is larger than the size of the incoming IP packet.

Which of the above statements is/are TRUE?
 A I and II only B I only C II and III only D II only
GATE CSE 2020   Computer Network
Question 7 Explanation:
 Question 8
Consider three machines M, N and P with IP addresses 100.10.5.2, 100.10.5.5 and 100.10.5.6 respectively. The subnet mask is set to 255.255.255.252 for all the three machines. Which one of the following is true?
 A M, N and P all belong to the same subnet B Only M and N belong to the same subnet C Only N and P belong to the same subnet D M, N, and P belong to three different subnets
GATE CSE 2019   Computer Network
Question 8 Explanation:
 Question 9
Consider an IP packet with a length of 4,500 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 _______.
 A 120 B 144 C 210 D 175
GATE CSE 2018   Computer Network
Question 9 Explanation:
 Question 10
Match with the suitable one:
$\begin{array}{|l|l|l|l|} \hline & \text { List-1 } & & \text { List-2 } \\ \hline \text { (a) } & \text { Multicast group membership } & \text { i. } & \text { Distance Vector routing } \\ \hline \text { (b) } & \text { Interior gateway protocol } & ii . & \text { IGMP } \\ \hline \text { (c) } & \text { Exterior gateway protocol } & iii . & \text { OSPF } \\ \hline \text { (d) } & \text { RIP } & iv . & \text { BGP } \\ \hline \end{array}$
 A a-ii, b-iii, c-iv, d-i B a-ii, b-iv, c-iii, d-i C a-iii, b-iv, c-i, d-ii D a-iii, b-i, c-iv, d-ii
ISRO CSE 2017   Computer Network
Question 10 Explanation:
There are 10 questions to complete.