Network Layer

Question 11

Host A (on TCP/IP v4 network A) sends an IP datagram D to host B (also on TCP/IP v4 network B). Assume that no error occurred during the transmission of D. When D reaches B, which of the following IP header field(s) may be different from that of the original datagram D?

(i) TTL 
(ii) Checksum 
(iii) Fragment Offset

• (i) only
• (i) and (ii) only
• (ii) and (iii) only
• (i), (ii) and (iii)

Question 12

Every host in an IPv4 network has a 1-second resolution real-time clock with battery backup. Each host needs to generate up to 1000 unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a 50-bit globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around?

• 128
• 64
• 256
• 512

Question 13

An IP router with a Maximum Transmission Unit (MTU) of 1500 bytes has received an IP packet of size 4404 bytes with an IP header of length 20 bytes. The values of the relevant fields in the header of the third IP fragment generated by the router for this packet are

• MF bit: 0, Datagram Length: 1444; Offset: 370
• MF bit: 1, Datagram Length: 1424; Offset: 185
• MF bit: 1, Datagram Length: 1500; Offset: 37
• MF bit: 0, Datagram Length: 1424; Offset: 2960

Question 14

Station A needs to send a message consisting of 9 packets to Station B using a sliding window (window size 3) and go-back-n error control strategy. All packets are ready and immediately available for transmission. If every 5th packet that A transmits gets lost (but no acks from B ever get lost), then what is the number of packets that A will transmit for sending the message to B?

• 12
• 14
• 16
• 18

Question 15

The address resolution protocol (ARP) is used for

• Finding the IP address from the DNS
• Finding the IP address of the default gateway
• Finding the IP address that corresponds to a MAC address
• Finding the MAC address that corresponds to an IP address

Question 16

In a packet switching network, packets are routed from source to destination along a single path having two intermediate nodes. If the message size is 24 bytes and each packet contains a header of 3 bytes, then the optimum packet size is:

• 4
• 6
• 7
• 9

Question 17

Consider the given network implementation scenario. For the given classful NID 199.10.20.0/24, the requirement is to create 13 subnets. With given details, find the range of first and last valid IP in 15th subnet.

• 199.10.20.208 to 199.10.20.222
• 199.10.20.225 to 199.10.20.238
• 199.10.20.193 to 199.10.20.206
• Not of these

Question 18

The routing table of a router is shown below:

 Destination     Sub net mask 	     Interface
 128.75.43.0 	 255.255.255.0 	        Eth0
 128.75.43.0 	 255.255.255.128 	Eth1
 192.12.17.5 	 255.255.255.255 	Eth3
 default 	  	                Eth2

On which interfaces will the router forward packets addressed to destinations 128.75.43.16 and 192.12.17.10 respectively?

• Eth1 and Eth2
• Eth0 and Eth2
• Eth0 and Eth3
• Eth1 and Eth3

Question 19

Consider three IP networks A, B and C. Host HA in network A sends messages each containing 180 bytes of application data to a host HC in network C. The TCP layer prefixes a 20 byte header to the message. This passes through an intermediate net­work B. The maximum packet size, including 20 byte IP header, in each network is A : 1000 bytes B : 100 bytes C : 1000 bytes The network A and B are connected through a 1 Mbps link, while B and C are connected by a 512 Kbps link (bps = bits per second). Assuming that the packets are correctly delivered, how many bytes, including headers, are delivered to the IP layer at the destination for one application message, in the best case ? Consider only data packets.

• 200
• 220
• 240
• 260

Question 20

Consider three IP networks A, B and C. Host HA in network A sends messages each containing 180 bytes of application data to a host HC in network C. The TCP layer prefixes a 20 byte header to the message. This passes through an intermediate net­work B. The maximum packet size, including 20 byte IP header, in each network is A : 1000 bytes B : 100 bytes C : 1000 bytes The network A and B are connected through a 1 Mbps link, while B and C are connected by a 512 Kbps link (bps = bits per second). What is the rate at which application data is transferred to host HC? Ignore errors, acknowledgements, and other overheads.

• 325.5 Kbps
• 354.5 Kbps
• 409.6 Kbps
• 512.0 Kbps