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Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[5] Question 1: Describe the difference between OSPF and RIP, including what
information is sent where.
Function/Criteria
Transport protocol used
Class of algorithm used
Specific algorithm used
Metric
Sends information
about ___ to ____
RIP
UDP
Distance Vector
Bellmann-Ford
Hop
Distance to ALL nodes to
Neighbors
OSPF
Direct IP (Port 89)
Link State
Dijkstra
Cost (mostly bandwidth)
Link state to neighbors to
All nodes
[3] Question 2: What is a redirect message? Draw a schematic network to show how it is
used.
It is an ICMP message exchange to update the routing table to direct future datagrams to
the correct router (As shown in the following sketch).
Page 1 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[21] Question 3: Consider the following network. The Network Mask for both networks
(9.2.3.0 and 9.2.4.0) is 255.255.255.128. (=11111111.11111111.11111111.10000000B)
Note: Not all nodes in this internet are shown.
Spider
Cheetah
9.2.3.45
9.2.3.52
9.2.3.0
9.2.3.2
9.2.3.30
Viper
(router)
Cobra (router)
9.2.4.2
9.2.4.0
Rest of the
Internet
9.2.4.10
9.2.4.15
The routing table at node “Spider” looks as follows. Entry “1” signifies the “default”
value:
1
2
3
4
5
Network Address
NetMask
127.0.0.0
9.2.3.0
9.2.4.0
9.2.2.45
0.0.0.0
255.0.0.0
255.255.255.128
255.255.255.128
255.255.255.255
0.0.0.0
Gateway (Next Node)
Address
127.0.0.1
9.2.3.45
9.2.3.30
127.0.0.1
9.2.3.2
Interface
Interface-0
Interface-1
Interface-1
Interface-0
Interface-1
For each of the following destination IP addresses show the destination network address
(if known, otherwise designate Internet) and determine what node the IP datagram is send
to. Briefly justify your answer
(Continued on next page)
Page 2 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[3] Question 3.1: Destination IP = 9.2.4.13
Destination Net Address (if known): 9.2.4.0
Next Node: 9.2.3.30
Reason: Mask 255.255.255.128 matches row 4 of the routing table
[3] Question 3.2: Destination IP = 9.2.4.157
Destination Net Address (if known): unknown
Next Node: 9.2.3.2
Reason: no matching mask. The default entry (5) is used
[3] Question 3.3: Destination IP = 9.2.3.75
Destination Net Address (if known): 9.2.3.0
Next Node: sent directly to 9.2.3.75 through the link layer attached to 9.2.3.45
Reason: Mask 255.255.255.128 matches row 2
[3] Question 3.4: Destination IP = 9.2.3.176
Destination Net Address (if known): Same as 3.2
Next Node:
Reason:
[3] Question 3.5: Destination IP = 193.2.27.18
Destination Net Address (if known): Same as 3.2
Next Node:
Reason:
[3] Question 3.6: Destination IP = 9.2.6.7
Destination Net Address (if known): Same as 3.2
Next Node:
Reason:
[3] Question 3.7: Destination IP = 9.2.4.127
Destination Net Address (if known): Same as 3.2
Next Node:
Reason:
Page 3 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[8] Question 4: Consider the following internet configuration
Node A
Node B
Router R
IP Address
9.2.34.17
HW Address
1234
9.2.34.2
9.2.87.2
9.2.87.34
9765
345
4675
9.2.34.0
9.2.87.0
MTU = 1000 Bytes
MTU = 600 Bytes
Assume a single TCP segment of 900 bytes is delivered to the IP layer at node A to be
sent to node B. Show how this segment (and only this segment) is routed over networks
9.2.34.0 and 9,2,87.0. Clearly show the content of MAC frames (only the fields shown
below) over each network. In each frame specifically show the MAC (hardware)
addresses and IP addresses and other pertinent information in the following format. In the
“IP Header Info” part, only show content of the FLAG (May-Fragment and More bits)
and Fragment Offset.
Note: For the “Don’t Fragment” bit assume 0=May-Fragment and 1=May-NotFragment
For the “More” bit assume 1=More-Fragments to Come and 0=Last-Fragment
DST MAC
SRC MAC
IP Hdr Info
(More, Don’t Frag. Offset)
DST IP
SRC IP
Data Size
DST IP
9.2.87.34
SRC IP
9.2.34.17
IP Hdr Info
0
0
0
Data Size
920
From A to R:
DST MAC
9765
SRC MAC
1234
From R to B:
DST MAC
4675
SRC MAC
345
DST IP
9.2.87.34
SRC IP
9.2.34.17
IP Hdr Info
1
0
0
Data Size
476
DST MAC
4675
SRC MAC
345
DST IP
9.2.87.34
SRC IP
9.2.34.17
IP Hdr Info
0
0
52
Data Size
464
Page 4 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[16] Question 5: An ISP is allocated a class C IP address of network 192.168.16.0/24.
The ISP wishes to divide its address block so that to have
1.
At least 20 clients
2.
At least 5 hosts per client
Design an IP addressing scheme to meet the above requirements:
For your design answer the following:
Please note: you can write your answers in binary or decimal or mixed, whichever you
feel more comfortable. For example, all the followings are accepted:
192.168.16.12 or 192.168.16.00001100 or 11000000. 10101000.00010000,00001100
a- [2] Out of 8 bits, number of bits for client block=_5_; number of bits for host-id=_3_
b- [2] How many clients can the ISP support? : ____(2**5)=32 ___
c- [2] How many nodes (host) each client can have? :_[(2**3)-2 = 6] ___
d- [2] New network mask for each client (X.X.X.X): _255.255.255.248
(248=’11111000’B)
e- [2] Choose a host/node address of a client and specify the network mask using CIDR
notation (a.b.c.d/x): 192.168.16.10/24
f- [2] List 2 of the possible client subnet addresses (remember, you need to set the
“host” part of the address to “0”):
1- 192.168.16.0 (the first subnet)
2- 192.168.16.8 [the second subnet. This subnet was in fact used in part (e) ]
g- [3] Choose a client (subnet) from step f (please identify) and list 3 hosts addresses
(complete IP address) within that client
Client Subnetwork: ___ 192.168.16.8 _____
1-The first host address: 192.168.16.9 _
2-The last (highest) host address: 192.168.16.14 _
3- A host address rather than (1) and (2) above: _192.168.16.10 __
h- [1] For the subnet you chose for (g), indicate the broadcast address
Broadcast address: __192.168.16.15 __
Page 5 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[3] Question 6: Consider the following interconnected network (routers R1 to R7 and
networks A, B, C, D, E, F). Only routers in this internet are shown.
R2
Router:
G
A
R7
R1
E
B
R6
R3
F
C
R5
R4
D
Draw the logical network (graph) of this internet for the purpose of finding the optimal
route amongst the router. In your logical network, please identify the nodes and links
with identical routers’ and networks’ numbers as depicted above.
Page 6 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[4] Question 7: Suppose client A initiates a Telnet session with server S. At about the
same time, client B also initiates a Telnet session with server S. provide possible source
and destination port numbers for:
a) The segment sent from A to S
b) The segment sent from B to S
c) The segment sent from S to A
d) The segment sent from S to B
Source Port No,
x
y
23
23
Destination Port No.
23
23
x
y
e) If A and B are different hosts, is it possible that the source port number in the segments
from A to S is the same as that from B to S? (Yes or No!)
Yes
f) How about if they are the same host? (Yes or No!)
No
Page 7 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[4]- Question 8: You are using Telnet to access a host and the connection has already
been established. You type character “C” which appears on your screen and the cursor
moves one space ahead. For this process to complete, how many bytes are transmitted
across the network? Please consider the transport and the network layer overheads only,
no link later overhead). Assume no optimization is done (each segment is acknowledged
separately). Please draw the timeline of events.
Total 122 bytes
Page 8 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
[12] Question 9:
Consider the following network configuration
[2] Question 9.1:
In order to begin communication with the server, Host G sends out an ARP request. How
will the devices exhibited in the topology respond to this request (choose one)
1. ------- Hosts D and E will respond that the destination is not on the local LAN
2. ------- Router R2 will forward the ARP request to the R1 router
3. ------- The request is dropped, because the server is not on the LAN
4. ------- The R1 router will respond with the IP address of the WWW server
5. ---X-- Router R2 will response with the MAC address of its interface to LAN
[4] Question 9.2:
The ARP reply has been received by host G, which needs to build the packet. What
information will be placed in the header of the packet that leaves host G if host G is to
communicate with the WWW server (Choose two)
1. ------- The destination address will be the IP address of R1 router
2. ---X-- The destination address will be the IP address of the WWW server
3. ------- The destination address will be the IP address of the LAN interface of R2
4. ---X-- The source address will be the IP address of host G
5. ------- The source address will e the IP address of the LAN interface of R2
6. ------- the destination address will be the IP address of the LAN interface of R1
[4] Question 9.3
The frame has been received by R1 router and is to be delivered on the local LAN. Which
two statements describe the addressing of the Ethernet frame that has been created by R1
router? (Choose two)
1. ---X-- The destination address will be the MAC address of the WWW server
2. ------- The source address will be the MAC address of host G.
Page 9 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
3. ---X-- the source address will be the MAC address of the LAN interface of router R1
4. ------- The source address will be the address of the Internet (WAN) interface of R2
5. ------- The source address will be the address of the Internet (WAN) interface of R1
[2] Question 9.4:
Host G is displaying two World Wide Web documents from the WWW server in two
browser windows at the same time. How did the data find its way to the correct browser
windows? (Choose one)
1. ------- The IP source addresses of the packet will be used to direct the data to the
correct browser window.
2. ------- The browsers track the data by the URL.
3. ---X-- TCP port numbers are used to direct the data to the correct application window.
4. ------- Te OSI application layer tracks the conversations and directs them to the
correct browser.
[4] Question 10:
Which of the following describe private IP addresses? (Choose two)
1. ------- Addresses chosen by a company to communicate with the Internet.
2. ------- Addresses that cannot be routed through the public Internet
3. ------- Addresses that can be routed through the public Internet
4. ------- A scheme to conserve public addresses
5. ------- Addresses licensed to enterprises or ISPs by an Internet registry organization.
[3] Question 11:
What is the subnet address of 172.16.159.159/22?
1. ------- 172.16.0.0
2. ------- 172.16.128.0
3. ---X-- 172.16.156.0 [159= ‘10011111’B, the rightmost 2 bits are set to “0” by
masking, hence ‘10011100’B=156]
4. ------- 172.16.159.0
5. ------- 172.16.159.128
6. ------- 172.16.192.0
7. ------- None of the above
[4] Question 12:
Consider the following internet in which network N1 is connected to network N2 via
router R1.
1. Host A (on network N1) wants to send a datagram to host B on the same
Network, N1. How does A learn about the MAC address (hardware address) of
host B?
Answer: Through ARP, replied by R1
2. Now consider host A desiring to send a datagram to host C on network N2. How
does A learn about the MAC address of host C?
Answer: A does not need to know the MAC address of C
Page 10 of 11
Internetworking with TCP/IP Final Exam (Solution)
CS 6843- Fall 2009
C
N2
9.2.18.
A
B
R1
N1 9.2.16.
Page 11 of 11