Unit 9: Data Communication and Computer Networks · 19 questions · about 22 minutes. Press End Mock any time to see your score and the correct answers.
Consider two hosts P and Q 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 packet is allowed to be fragmented, meaning the Don't Fragment (DF) flag in the IP Header is not set by P. Which of the following statements is/are not 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) resend the fragment with IP Identification value of 0×1234
C. If the second fragment is lost then P is required to resend the entire TCP segment
D. TCP destination port can be determined by analyzing the second fragment only
Choose the correct answer from the options given below:
Correct answer: D. B and D Only
Two fragments of 820 and 620 bytes are created (A true), and TCP at P must resend the whole segment if one is lost (C true). Routers never resend fragments (B false), and the TCP ports are only in the first fragment (D false). The statements that are not true are B and D.
Note on the official key: the official key says option B. Official/PW key is B (A and C), which are the true statements; the question asks for the statements that are not true. (The same question in June 2023 asks for the true ones, with key B.)
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 forms frames; network layer controls the subnet; transport layer carries data connection-oriented or connectionless.
Consider two hosts P and Q 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 of 1400 bytes is transferred from P to Q through R with IP identification value of 0x1234. Assume that IP header size is 20 bytes. Further, the packet 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 statements is/are true
I. Two fragments are created at R and IP datagram size carrying the second fragment is 620 bytes
II. If the second fragment is lost then R resends the fragment with IP Identification value of 0x1234
III. If the second fragment is lost then P is required to resend the entire TCP segment
IV. TCP destination port can be determined by analyzing the second fragment only
Correct answer: B. I and III only
R creates two fragments, of 820 and 620 bytes (I true). IP does not retransmit, so TCP at P resends the whole segment (III true). Routers never resend (II false), and only the first fragment carries the TCP ports (IV false).
Directions (Q91–95): An organization is granted the block 130.56.0.0/16. The administrator wants to create 1024 subnets.
Find first and last addresses of First subnet. q
Correct answer: B. 130.56 .0 .0 & 130.56 .0 .63
The first /26 subnet starts at 130.56.0.0 and has 64 addresses, ending at 130.56.0.63.
Find subnet mask. q
Correct answer: A. 255 .255 .255.192
/26 is 26 one-bits: 255.255.255.192.
Find first and last addresses of last subnet. Q
Correct answer: D. 130 .56 .255 .192 & 130.56 .255 .255 Q Directions (96-100) Read the following passage and answer the given questions. A Turing Machine for the language L=anbmcndm|n ≥1, m≥1 is designed. The resultant model is M=({q ,q ,q ,q ,q ,q ,q ,q ,q }),{a,b,c,d}, 0 1 2 3 4 5 6 7 f {a,b, c,d,X , X ,Y ,Y }, δ, q , B,{ q } and part of ' δ ' is 1 2 1 2 0 f Q given in the transition table. You need to write the following questions based on design of Turing Machine for the given language. Note that, while designing the Turing Machine X and 1 X are used to work with 'a's and 'c's and Y and 2 1 Q Y are used to handle 'b's and 'd's of the given 2 string. q2 (q2, a, (q2, b, (q2, (q2,x2,L) L) L) X1, R)
The last /26 block in 130.56.0.0/16 is 130.56.255.192 to 130.56.255.255.
A classless address is given as 167.199.170.82/27. The number of addresses in the network is
Correct answer: B. 32 addresses
/27 leaves 32 − 27 = 5 host bits: 2⁵ = 32 addresses.
Match List I with List II. List I: A. Data link layer, B. Network layer, C. Transport layer, D. Session layer. List II: I. True end-to-end layer, II. Token management, III. Produce billing information, IV. Piggybacking.
Correct answer: A. A ‐ IV, B ‐ III, C ‐ I, D ‐ II
Piggybacking ACKs is a data-link technique; the network layer can count packets for billing; the transport layer is the true end-to-end layer; the session layer manages tokens.
The address of class B host is to be split into 6 bit subnets with ‐ subnet number. What is the maximum number of the subnets and the maximum number of hosts in each subnet?
Correct answer: D. 62 subnets and 1022 hosts
6 subnet bits give 2⁶ − 2 = 62 subnets (classic rule); the remaining 10 host bits give 2¹⁰ − 2 = 1022 hosts.
Match List I with List II. List I: A. Serial Line IP (SLIP), B. Border Gateway Protocol (BGP), C. User Datagram Protocol (UDP), D. Simple Network Management Protocol (SNMP). List II: I. Application layer, II. Transport layer, III. Data link layer, IV. Network layer.
Correct answer: B. A-III, B-IV, C-II, D-I
SLIP frames IP over serial lines (data link); BGP is an inter-domain routing protocol (network layer); UDP is a transport protocol; SNMP is an application-layer protocol.
Which of the following class of IP address has the last address as 223.255 .255 .255 ?
Correct answer: C. Class C
Class C spans 192.0.0.0 to 223.255.255.255.
Consider a subnet with 720 routers. If a three- level hierarchy is chosen, with eight clusters, each containing 9 regions of 10 routers, then total number of entries in hierarchical table of each router is
Correct answer: A. 25
Each router keeps 10 entries for routers in its own region, 8 for the other regions in its cluster, and 7 for the other clusters: 10 + 8 + 7 = 25.
What is the name of the protocol that allows a client to send a broadcast message with its MAC address and receive an IP address in reply?
Correct answer: C. RARP
RARP lets a host broadcast its MAC address and receive its IP address.
You need 500 subnets, each with about 100 usable host addresses per subnet. What network mask will you assign using a class B network address?
Correct answer: B. 255.255.255.128
500 subnets need 9 bits; 7 bits remain for hosts (126 usable). /25 = 255.255.255.128.
Consider the following two statements with respect to IPv4 in computer networking : P: The loopback (IP) address is a member of the class B network. Q: The loopback (IP) address is used to send a packet from the host to itself. What can you say about the statements P and Q?
Correct answer: B. P-False; Q-True
Loopback 127.0.0.0/8 is in the class A range, so P is false. It sends packets from a host to itself (Q true).
What percentage % of the IPv4, IP address space do all class C addresses consume?
Correct answer: A. 12.5%
Class C addresses start with 110, one eighth of the address space: 12.5%.
The four byte IP Address consists of
Correct answer: C. Both Network and Host Addresses
An IPv4 address has a network part and a host part.
An ISP has the CIDR block 245.248.128.0/20. It wants to give half of it to organization A and a quarter to organization B, keeping the rest. Which is a valid allocation to A and B?
Correct answer: A. 245.248.136.0/21 and 245.248.128.0/22
The /20 spans 245.248.128.0–143.255. Half is a /21 and a quarter a /22. A gets 136.0/21 (136–143) and B gets 128.0/22 (128–131); they don't overlap and the ISP keeps 132–135.
The dotted-decimal notation of the following IPV4 address in binary notation is _________.10000001 00001011 00001011 11101111
Correct answer: C. 129.11.11.239
10000001 = 129, 00001011 = 11, 00001011 = 11, 11101111 = 239: 129.11.11.239.
