CS2302 – COMPUTER NETWORKS
TWO MARKS
UNIT-V- Email (SMTP, MIME, IMAP, POP3) – HTTP – DNS- SNMP – Telnet –
FTP – Security –PGP - SSH
1. What is the function of SMTP?
The TCP/IP
protocol supports electronic mail on the Internet is called Simple Mail
Transfer (SMTP). It is a system for sending messages to other computer users
based
on e-mail addresses. SMTP
provides mail exchange between users on the same or different computers.
2. What is the difference between a user agent (UA) and a mail transfer
agent (MTA)?
The
UA prepares the message, creates the envelope, and puts the message in the
envelope. The MTA transfers the mail across the Internet.
3. How does MIME enhance SMTP?
MIME
is a supplementary protocol that allows non-ASCII data to be sent through SMTP.
MIME transforms non-ASCII data at the sender site to NVT ASCII data and
deliverers it to the client SMTP to be sent through the Internet. The server
SMTP at the receiving side receives the NVT ASCII data and delivers it to MIME
to be transformed back to the original data.
4. Why is an application such as POP needed for electronic messaging?
Workstations
interact with the SMTP host, which receives the mail on behalf of every host in
the organization, to retrieve messages by using a client-server protocol such
as Post Office Protocol, version 3(POP3). Although POP3 is used to download
messages from the server, the SMTP client still needed on the desktop to
forward messages from the workstation user to its SMTP mail server.
5. Give the format of HTTP request message?
6. What is the purpose of
Domain Name System?
Domain Name System
can map a name to an address and conversely an address to name.
7. Discuss the three main division of the domain name space.
Domain name
space is divided into three different sections: generic domains, country
domains & inverse domain.
Generic domain: Define
registered hosts according to their generic behavior, uses generic suffixes.
Country domain: Uses two
characters to identify a country as the last suffix.
Inverse domain: Finds the
domain name given the IP address.
8. Discuss the TCP connections needed in FTP.
FTP establishes
two connections between the hosts. One connection is used for data transfer,
the other for control information. The control connection uses very simple
rules of communication. The data connection needs more complex rules due to the
variety of data types transferred.
9. Discuss the basic model of FTP.
The client has
three components: the user interface, the client control process, and the
client data transfer process. The server has two components: the server control
process and the server data transfer process. The control connection is made
between the control processes. The data connection is made between the data
transfer processes.
10. Name four factors needed for a secure network?
Privacy: The sender and the receiver
expect confidentiality.
Authentication: The receiver is
sure of the sender’s identity and that an imposter has not sent the message.
Integrity: The data must arrive
at the receiver exactly as it was sent.
Non-Reputation: The receiver must
able to prove that a received message came from a specific sender.
11. How is a secret key different from public key?
In secret key,
the same key is used by both parties. The sender uses this key and an
encryption algorithm to encrypt data; the receiver uses the same key and the
corresponding decryption algorithm to decrypt the data. In public key, there
are two keys: a private key and a public key. The private key is kept by the
receiver. The public key is announced to the public.
12. What is a digital signature?
Digital
signature is a method to authenticate the sender of a message. It is similar to
that of signing transactions documents when you do business with a bank. In
network transactions, you can create an equivalent of an electronic or digital
signature by the way you send data.
13. What are the advantages & disadvantages of public key
encryption?
Advantages:
a)
Remove the restriction of a shared secret key between two entities. Here each
entity can create a pair of keys, keep the private one, and publicly distribute
the other one.
b) The no. of keys needed is reduced
tremendously. For one million users to communicate, only two million keys are
needed.
Disadvantage:
If
you use large numbers the method to be effective. Calculating the cipher text
using the long keys takes a lot of time. So it is not recommended for large
amounts of text.
14. What are the advantages & disadvantages of secret key
encryption?
Advantage:
Secret
Key algorithms are efficient: it takes less time to encrypt a message. The
reason is that the key is usually smaller. So it is used to encrypt or decrypt
long messages.
Disadvantages:
a)
Each pair of users must have a secret key. If N people in world want to use
this method, there needs to be N (N-1)/2 secret keys. For one million people to
communicate, a half-billion secret keys are needed.
b)
The distribution of the keys between two parties can be difficult.
15. Define permutation.
Permutation
is transposition in bit level.
Straight permutation: The no. of
bits in the input and output are preserved.
Compressed permutation: The no.
of bits is reduced (some of the bits are dropped).
Expanded permutation: The no. of
bits is increased (some bits are repeated).
16. Define substitution & transposition
encryption?
.
Substitution: A character level encryption in which each
character is replaced by another character in the set.
Transposition: A Character level
encryption in which the characters retain their plaintext but the position of
the character changes.
17. Define CGI?
. CGI is a standard for communication between HTTP servers
and executable programs. It is used in crating dynamic documents.
18. What are the requests messages support SNMP and explain it?
·
GET
·
SET
The former is
used to retrieve a piece of state from some node and the latter is used to
store a new piece of state in some node.
19. Define SSH?
Secure
Shell is used to provide a remote login, and used to remotely execute commands
and transfer files and also provide strong client/server authentication /
message integrity.
20. Give the format of HTTP response message?
The client has three components: the user
interface, the client control process, and the client data transfer process.
The server has two components: the server control process and the server data
transfer process. The control connection is made between the control processes.
The data connection is made between the data transfer processes.
22.What is a digital signature?
Digital signature is a method to authenticate
the sender of a message. It is similar to that of signing transactions
documents when you do business with a bank. In network transactions, you can
create an equivalent of an electronic or digital signature by the way you send
data.
23.Draw the diagram
foe explain security
24. Define
Cryptography
n
Cryptography
refers to the science and art of transforming messages to make them secure and
immune to attacks.
n
Original
message before being transformed is called plaintext.
n
After
the message is transformed, is called ciphertext.
n
An
encryption algorithm transforms the plaintext to ciphertext; a decryption
algorithm transforms the ciphertext back to plaintext.
n
The
term cipher is used to refer to encryption and decryption algorithms.
25. What are the
types of DNS Message
n
Two
types of messages
Query: header and question
records
n
Response:
Header, question records, answer records, authoritative records, and additional
records.
26. What is TELNET
PROTOCOL?
A TELNET connection is a Transmission Control Protocol (TCP) connection used to transmit data with interspersed TELNET control information.
The TELNET Protocol is built upon three main ideas: first, the concept of a "Network Virtual Terminal"; second, the principle of negotiated options; and third, a symmetric view of terminals and processes.
27. What is PGP?
Pretty Good Privacy. A program using public key encryption
popularly used with email
A high security RSA public-key
encryption application for MS-DOS, Unix, VAX/VMS, and
other computers. It was written by Philip R. Zimmermann of Phil's Pretty Good(tm) Software and later
augmented by a cast of thousands, especially including Hal Finney, Branko
Lankester, and Peter Gutmann.
28. What is POP3?
POP3 (Post Office Protocol 3) is the most recent version
of a standard protocol for receiving e-mail. POP3 is a client/server
protocol
in which e-mail is received and held for you by your Internet server. POP and
IMAP deal with the receiving of e-mail and are not to be confused with the
Simple Mail Transfer Protocol (SMTP),
a protocol for transferring e-mail across the Internet.
29. What is IMAP.
IMAP (Internet Message Access Protocol) is a standard protocol
for accessing e-mail
from your local server. IMAP (the latest version is IMAP Version 4) is a client/server
protocol in which e-mail is received and held for you by your Internet server.
IMAP can be thought of as a remote file server. POP3 can
be thought of as a "store-and-forward" service.
30. What is SSH?
(Secure Shell) A security protocol for
logging into a remote server. SSH provides an encrypted session for
transferring files and executing server programs. Also serving as a secure
client/server connection for applications such as database access and e-mail
SSH supports a variety of authentication methods.
ALSO READ ..!
UNIT I NOTES
UNIT II NOTES
UNIT III NOTES
UNIT IV NOTES
UNIT V NOTES
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