Download CN-II_T2_SOLUTION

USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
INTERNAL ASSESSMENT TEST –2
Scheme and Solution
Subject & Code : Computer Networks-II (10CS64)
Name of faculty: Mrs. Sarasvathi V
1.
Briefly explain the following
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Remote Login Protocols
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SMTP protocol
Solution Telnet – 3Marks, SSH- 2 Marks, SMTP Diagram- 2Marks, SMTP explanation 3Marks
Telnet
A client/Server can create a mechanism that allows a user to establish a session on the
remote machine and then run its applications.
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TELNET has the following properties.
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Client programs are built to use the standard client/server interfaces.
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Client and a server can negotiate data format options.
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Once a connection is established through TELNET, both ends of the
connection are treated symmetrically.
Characters are sent to TELNET client, which transforms characters to a universal
character set called network virtual terminal(NVT), and delivers them to local
TCP/IP stack
Secure Shell protocol
– Based on UNIX programs.
– Uses TCP for communications.
SSH has the following advantages over TELNET.
– SSH provides a secure communication by encrypting and authenticating
messages.
– Additional data transfers over the same connection by multiplexing
multiple channels that are used for remote login.
– SSH security is implemented by using public-key encryption.
B.E VI A, B & C Section
10
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
SMTP
Begin SMTP Between Two Users
1. User 1 provides user 2's e-mail address ([email protected]) and
composes its message.
2. User 1 sends the message to its mail server (isp.com).
3. Server isp.com places the message in its queue.
4. SMTP on user 1's mail server notices the message in the queue and opens a TCP
connection with the organization mail server (organization.com).
5. Initial SMTP handshaking takes place between the two servers.
6. The message is sent to organization.com's mail server, using the established TCP
connection.
7. User 2's mail server receives the message and then puts it in user 2's mailbox,
ready to be retrieved by user 2.
2
Explain MIB & SNMP messages
Solution
MIB - 3marks, SNMP seven PDUs - 5 Marks, SNMP PDU format diagram and
Explanation - 3 Marks
MIB
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Management information base (MIB) is an information storage medium that
contains managed objects reflecting the current status of the network.
Objects are organized in a hierarchical manner and are identified by the abstract
syntax notation one (ASN.1) object definition language.
B.E VI A, B & C Section
10
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
•
The hierarchy of object names, known as ASN.1 object identifier, is an object
identifier tree in which each branch has both a name and a number.
• Network management can then identify an object by a sequence of names or
numbers from the root to that object.
SNMPv2 has seven PDUs, or messages, as follows.
1. GetRequest is used to obtain a MIB object value.
2. GetNextRequest is used to obtain the next value of a MIB object.
3. GetBulkRequest gets multiple values, equivalent to multiple GetRequests but
without using multiple overheads.
4. InformRequest is a manager-to-manager message that two communicating
management centers are remote to each other.
5. SetRequest is used by a managing center to initiate the value of a MIB object.
6. Response is a reply message to a request-type PDU.
7. Trap notifies a managing center that an unexpected event has occurred.
SNMP PDU format
Two types of PDUs are depicted: Get or Set and Trap. The Get or Set PDU format is as
follows:
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PDU type indicates one of the seven PDU types.
Request ID is an ID used to verify the response of a request. Thus, a managing
center can detect lost requests or replies.
Error status is used only by Response PDUs to indicate types of errors reported
by an agent.
Error index is a parameter indicating to a network administrator which name has
caused an error.
B.E VI A, B & C Section
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
3
a
Explain the RSA algorithm. Apply RSA encrypt a=3 , b=11, x=7, M=5
1. Choose two roughly 256-bit prime numbers, a and b, and derive n = ab. (A
number is prime if it has factors of 1 and itself.). Plain Text m is represented by a
number must be less than n.
2. Find x. Select encryption key x such that x and (a - 1)(b - 1) are relatively prime.
(Two numbers are relatively prime if they have no common factor greater than
1.)
3. Find y. Calculate decryption key y:
6
4. At this point, a and b can be discarded.
5. The public key = {x, n}.
6. The private key = {y, n}.
Encryption
• Both sender and receiver must know the value of n.
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The sender knows the value of x, and only the receiver knows the value of y.
• Given m<n, ciphertext c is constructed by
Decryption
• Given the ciphertext, c, the plaintext, m, is extracted by
Problem Solution
a=3 b=11 x=7, m=5
n= 33
7ymod20=1
Y=3
Public key = { 7,33}
Private key = { 3,33}
C= 57mod33
C=14
M=143mod33
M=5
3.
b
Explain the Diffie- Hellman Key exchange process
4
B.E VI A, B & C Section
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
4.
a
What are Ad-hoc networks? Mention their application types and unique features.
Definition – 1Marks, Application -2 Marks, features-2 Marks
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The establishment of a network anywhere and anytime, without any fixed
infrastructure to support the mobility of the users in the network.
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A collection of mobile nodes with a dynamic network infrastructure forming a
temporary network.
Applications
• Rescue operations.
• Military –battle zone
• Law enforcement and security operations.
• Home networks
• Conferencing.
Features
 Automatic discovery of available services
 self-stabilization
 multicast a message to many users efficiently
B.E VI A, B & C Section
5
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
4
b
Give the classification of routing protocols and list out the table driven and source
initiated routing protocols.
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Centralized versus distributed.
– In centralized routing protocols, the routing decision is made at a central
node.
– In distributed routing protocols, the routing decision is made by all the
network nodes.
– Routing protocols in most efficiently designed ad-hoc networks are
distributed to increase the reliability of the network. In such cases, nodes
can enter or leave the network easily, and each node can make routing
decisions, using other collaborative nodes.
Static versus adaptive.
– In static routing protocols, a route of a source/destination pair does not
change because of any traffic condition or link failure. In adaptive routing
protocols, routes may change because of any congestion.
Whether a protocol is centralized, distributed, static, or adaptive, it can generally be
categorized as either table driven or source initiated.
Table-driven, or proactive, routing protocols
• Table-driven, or proactive, routing protocols find routes to all possible
destinations.
• The routes are recorded in the nodes' routing tables and are updated within the
predefined intervals.
Source-Initiated Routing Protocols
• Source-initiated, or reactive, routing protocols, are on-demand procedures and
create routes only when requested to do so by source nodes.
• A route request initiates a route-discovery process in the network and is
completed once a route is discovered.
• On-demand protocols are more suitable for ad-hoc networks. In most cases,
reactive protocols are desired.
The table-driven protocols
– The Destination-Sequenced Distance Vector (DSDV) protocol
– The Cluster-Head Gateway Switch Routing (CGSR) protocol
– The Wireless Routing Protocol (WRP).
The source-initiated protocols
– the Dynamic Source Routing (DSR) protocol.
– the Associative-Based Routing (ABR) protocol
– Temporally Ordered Routing Algorithm (TORA)
B.E VI A, B & C Section
5
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
–
5
Ad-Hoc On-Demand Distance Vector (AODV) protocol.
Explain the following protocols in detail
A) CGSR
B) DSR
CGSR diagram – 2 Marks, Explanation – 3 Marks, DSR diagram -2 Marks,
Explanation -2 Marks
CGSR
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DSR
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Each predefined number of nodes are formed into a cluster controlled by a
cluster head, which is assigned using a distributed clustering algorithm.
A cluster head can be replaced frequently by another node, for several reasons,
such as lower-level energy left in the node or a node moves out of contact.
Each node maintains two tables: a cluster-member table and a routing table.
The cluster-member table records the cluster head for each destination node
the routing table contains the next hop to reach the destination.
A node is required to find the best route over cluster heads from the clustermember table.
It is an on-demand, or source-initiated routing protocol.
DSR has two phases: route discovery and route maintenance
B.E VI A, B & C Section
10
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Computer Science And Engineering
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The node first broadcasts a route-request packet, including the destination
address, source address, and a unique identification number.
When it receives a route-request packet, the neighboring node it looks at its
table. If it has a path to destination, then send route reply.
The node adds its own address to the preassigned field of the route-request
packet and forwards it to its neighboring nodes.
Destination node generates a route-reply packet, which contains a route record
of the sequence of nodes taken from the source to this node.
Once the source receives all the route-reply packets, it updates its routing table
with the best path to the destination and sends its packets through that selected
route.
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B.E VI A, B & C Section