Unit 9: Data Communication and Computer Networks · 21 questions · about 25 minutes. Press End Mock any time to see your score and the correct answers.
Correct answer: D. B and D Only
Correct answer: C. A-III, B-I, C-II, D-IV
Correct answer: B. I and III only
Directions (Q91–95): An organisation is granted the block 130.56.0.0/16. The administrator wants to create 1024 subnets.
Correct answer: B. 64
Correct answer: A. 130.56
Correct answer: B. 130.56.0.0 & 130.56.0.63
Correct answer: A. 255.255.255.192
Correct answer: D. 130.56.255.192 & 130.56.255.255
Correct answer: B. 32
Host A (on TCP/IPv4 Networks) send an IP Datagram D to host B (also on TCP/IPv4 network). Assume that no error occured during transmission of D, when D reaches B. Which of following header field may differ from that of original datagram D ?
(A) TTL
(B) Checksum
(C) Fragment offset
(D) Source IP
(E) Destination IP
Correct answer: B. (A), (B) and (C) Only
Each router decrements TTL and therefore recomputes the header checksum; if the datagram is fragmented on the way, the fragment offset changes. Source and destination addresses stay the same (without NAT).
Match List - I with List - II.
Correct answer: D. (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
First octet 1–126 is class A (10), 128–191 class B (180), 192–223 class C (210), and 240–255 class E (252).
Two computers A and B are configured as follows : A has IP address 203.197.2.53 and subnet mask 255.255.128.0, B has IP address 203.197.75.201 and subnet mask 255.255.192.0. What one of the following statement is true?
Correct answer: C. A assumes, B is on same network, but B assumes, A is on a different network
A uses /17: 203.197.2.53 and 203.197.75.201 both give 203.197.0.0 (third octets 2 and 75 are below 128), so A thinks B is local. B uses /18: B's network is 203.197.64.0 but A gives 203.197.0.0, so B thinks A is on a different network.
An IPv4 packet has arrived with the first few hexadecimal digits as shown below. How many hops can this packet travel before being dropped? The data belong to what upper-layer protocol? ( 5400001800100110040601...) 16
Correct answer: D. 4 hops, TCP
Byte 9 (TTL) is 04 and byte 10 (protocol) is 06. TTL 4 means 4 more hops; protocol 6 is TCP.
What is the total delay (latency) for a frame size of 10 million bits that is being set up on a link with 20 routers, each having a queuing time of 2 μ μs s and a processing time of 1 ? The length of link 5000 km. The speed of light inside the link is 2 * 108 m /s. The link has bandwidth of 6 Mbps.
Correct answer: B. 1.691726 s
Transmission: 10⁷ ÷ (6 × 10⁶) = 1.666667 s. Propagation: 5 × 10⁶ m ÷ 2 × 10⁸ m/s = 0.025 s. Routers: 20 × (2 + 1) μs = 60 μs. Total ≈ 1.691727 s.
Given below are two statements:
Statement (I) : In datagram networks - routers hold state information about connections
Statement (II) : In a virtual circuit network- each virtual circuit requires router table space per connection In the light of the above statements, choose the most appropriate answer from the options given below :
Correct answer: D. Statement I is incorrect but Statement II is correct Directions (91-95) Read the following passage and answer the given questions. Food X contains 6 units of Vitamin D per gram and 7 units of Vitamin E per gram and cost is Rs 12 per gram. Food Y contains 8 units of vitamin D per gram and 12 units of Vitamin E per gram and cost is Rs 20 per gram. The daily minimum requirements of vitamin D and E are 100 units and 120 units respectively. Suppose x is the quantity (in gram) of food X, y is quantity (in gram) of food Y. Answering the following question based on the above paragraph given.
Datagram routers keep no per-connection state (Statement I false); virtual-circuit networks need table entries in every router for every circuit (Statement II true).
Match List I with List II
Correct answer: C. A-III B-I C-II D-IV
Physical layer transmits raw bits; data link layer packs bits into frames; network layer controls the operation of the subnet; transport layer carries data connection-oriented or connectionless.
Consider two hosts P and Q that are connected through a router R. The maximum transfer unit (MTU) value of the link between P and R is 1500 bytes and between R and Q is 820 bytes. A TCP segment of size 1400 bytes is transferred from P to Q through R with IP identification value of 0 × 1234 . Assume that IP header size is 20 bytes. Further the pcaket is allowed to be fragmented that is Don't fragment (DF) flag in the IP Header is not set by P. Which of the following statement/s is/are true?
A. Two fragments are created at R and IP datagram size carrying the second fragment is 620 bytes
B. If the second fragment is lost, then R resends the fragment with IP identification value of 0 × 1234
C. If the second fragment lost, then P requires to resend the entire TCP segment.
D. TCP destination port can be determined by analyzing the second fragment only.
Correct answer: B. A and C only
The 1400-byte TCP segment plus a 20-byte header crosses the 820-byte MTU link in two fragments: 800 data bytes (820 total) and 600 data bytes (620 total), so A is true. Routers do not retransmit, and IP has no retransmission, so TCP at P resends the whole segment (C true, B false). The TCP header with the ports is only in the first fragment (D false).
Directions (Q96–100): An IP datagram arrives with the following partial header (hexadecimal): 45 00 00 54 00 03 00 00 20 06 …
What is the protocol of the payload being carried by the packet?
Correct answer: C. TCP protocol
Byte 10 is the protocol: 0x06 = TCP.
Which protocol is used to acquire the MAC Address of a host whose IP address is known?
Correct answer: B. Address Resolution Protocol
ARP maps a known IP address to its MAC address. RARP does the reverse.
Consider a computer network using the distance vector routing algorithm in its network layer. The Objective is to find the shortest cost path from router R to routers P and Q. Assume that R does not initially know the shortest routes to P and Q. R Assume that has three neighboring routers, X, Y Z R namely: and . During one iteration measures its distance as 3,2 , and 5 from its X, Y Z R neighbors and , respectively. Router getting routing vectors from its neighbors that indicates a distance of 7,6 and 5 from router X, Y Z P and to router , respectively. The routing vector also indicates that the distance to Q X, Y Z router from Routers and are 4, 6, 8 respectively. Which of the following statements is/are Ture with respect to the new routing table R at router after updation during this iteration. R P
A. The distance from to will be stored as 10 R Q
B. The distance from to will be stored as 7 R P
C. The next hop router for a packet from to Y is R Q
D. The next hop router for a packet from to Z is
Choose the correct answer from the options given below:
Correct answer: A. B and C only
To P: via X 3 + 7 = 10, via Y 2 + 6 = 8, via Z 5 + 5 = 10, so 8 via Y. To Q: via X 3 + 4 = 7, via Y 2 + 6 = 8, via Z 5 + 8 = 13, so 7 via X. B and C are true.
An organization's routing table has: 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. Which prefixes can be used together to aggregate all these subnets? A. 12.20.164.0/20 B. 12.20.164.0/22 C. 12.20.164.0/21 D. 12.20.168.0/22
The subnets cover third octets 164–167 (164/22 includes 166/23) and 168–171 (168/23 and 170/23). These are exactly 12.20.164.0/22 and 12.20.168.0/22. A /20 or /21 starting at 164 is not aligned to a valid block boundary.
