EBK COMPUTER NETWORKING
7th Edition
ISBN: 8220102955479
Author: Ross
Publisher: PEARSON
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Question
Chapter 2, Problem P17P
a)
Program Plan Intro
UIDL POP3 Command:
UIDL stands for Unique-Id Listing.
- The fact that optional UIDL command is supported is indicated by the UIDL capability.
- A unique number to each incoming mail message are assigned by POP3 servers.
- When a POP3 client issues the UIDL command, the server responds with the unique message ID in mailbox.
- The UIDL POP3 Command is used for “download and keep”, which allows mail to be left on the server after it has been downloaded to the user. Both the mail client and the POP server must support this feature.
- The client can use the UIDL command to determine which messages on the server has already been seen by maintaining a file that lists the messages received during earlier sessions.
Given transaction:
Suppose one has configured their POP mail client to operate in the download-and-delete mode. The transaction is given as below:
C: list (client asks server to list the size of each of the stored messages)
S: 1 498 (Server lists the size of message 1)
S: 2 912 (Server lists the size of message 2)
S: .
C: retr 1 (Client requests to read message 1)
S: blah blah … (Sends message 1)
S: ………blah
S: .
b)
Program Plan Intro
UIDL POP3 Command:
UIDL stands for Unique-Id Listing.
- The fact that optional UIDL command is supported is indicated by the UIDL capability.
- A unique number to each incoming mail message are assigned by POP3 servers.
- When a POP3 client issues the UIDL command, the server responds with the unique message ID in mailbox.
- The UIDL POP3 Command is used for “download and keep”, which allows mail to be left on the server after it has been downloaded to the user. Both the mail client and the POP server must support this feature.
- The client can use the UIDL command to determine which messages on the server has already been seen by maintaining a file that lists the messages received during earlier sessions.
Given transaction:
Suppose one has configured their POP mail client to operate in the download-and-keep mode. The transaction is given as below:
C: list (client asks server to list the size of each of the stored messages)
S: 1 498 (Server lists the size of message 1)
S: 2 912 (Server lists the size of message 2)
S: .
C: retr 1 (Client requests to read message 1)
S: blah blah … (Sends message 1)
S: ………blah
S: .
c)
Program Plan Intro
UIDL POP3 Command:
UIDL stands for Unique-Id Listing.
- The fact that optional UIDL command is supported is indicated by the UIDL capability.
- A unique number to each incoming mail message are assigned by POP3 servers.
- When a POP3 client issues the UIDL command, the server responds with the unique message ID in mailbox.
- The UIDL POP3 Command is used for “download and keep”, which allows mail to be left on the server after it has been downloaded to the user. Both the mail client and the POP server must support this feature.
- The client can use the UIDL command to determine which messages on the server has already been seen by maintaining a file that lists the messages received during earlier sessions.
Given transaction:
Suppose one configured the POP mail client to operate in the download-and-keep mode. Then using the transcript in part b, suppose one retrieves messages 1 and 2, exit POP, and then five minutes later can again access POP to retrieve new e-mail. The given transaction is:
C: list (client asks server to list the size of each of the stored messages)
S: 1 498 (Server lists the size of message 1)
S: 2 912 (Server lists the size of message 2)
S: .
C: retr 1 (Client requests to read message 1)
S: blah blah … (Sends message 1)
S: ………blah
S: .
C: retr 2
S: blah blah …
S: ………..blah
S: .
C: quit
S: +OK POP3 server signing off
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Students have asked these similar questions
Consider accessing your e-mail with POP3. Suppose you have configured your mail client to
operate in the 'download-and-delete' mode. When the client (C) fetches all emails from the server
(S), the sequence of messages exchanged starts as follows.
C: list
S: 1 498
S: 2 912
S:
C: retr 1
S: blah blah
S:
How many messages does the server store for the client?
blah
It cannot be known
912
498
None of the mentioned
The Kerberos Authentication Server might reject an AS_REQ message and instead require pre-authentication - that is, it requires the client to send a timestamp encrypted with the client key. Why does it do this?
Select one:
a. It must not disclose the Ticket Granting Ticket before the client has authenticated
b. It is dangerous to respond to an AS_REQ message before the client has authenticated
c. Responding to multiple AS_REQ messages would allow a guessed plaintext attack
d. It needs the client's public key to check the pre-authentication message was signed correctly
Kerberos is a protocol that is based around Needham-Schroeder protocol for many to
many authentications. Now answer the following questions. (Use necessary diagrams
to justify your answers)
i) Explain why the password of the user is not sent over the network and instead
session keys are generated and shared in the Kerberos protocol.
ii) The information in a TGT (Ticket Granting Ticket) is encrypted so the client
cannot access the information in the TGT. However, all information in the
ticket is already known to the client. Why is it still necessary to encrypt it?
iii) Describe the working mechanism of how a ticket is generated between the
client and server by the TGS (Ticket Granting Server) and how it is used for
client-server communication.
Chapter 2 Solutions
EBK COMPUTER NETWORKING
Ch. 2 - List five nonproprietary Internet applications and...Ch. 2 - Prob. R2RQCh. 2 - Prob. R3RQCh. 2 - Prob. R4RQCh. 2 - Prob. R5RQCh. 2 - Prob. R6RQCh. 2 - Prob. R7RQCh. 2 - Prob. R8RQCh. 2 - Prob. R9RQCh. 2 - Prob. R10RQ
Ch. 2 - Why do HTTP, SMTP, and POP3 run on top of TCP...Ch. 2 - Prob. R12RQCh. 2 - Prob. R13RQCh. 2 - Prob. R14RQCh. 2 - Prob. R15RQCh. 2 - Prob. R16RQCh. 2 - Prob. R17RQCh. 2 - From a users perspective, what is the difference...Ch. 2 - Prob. R19RQCh. 2 - Prob. R20RQCh. 2 - Prob. R21RQCh. 2 - Prob. R22RQCh. 2 - Prob. R23RQCh. 2 - Prob. R24RQCh. 2 - Prob. R25RQCh. 2 - In Section 2.7, the UDP server described needed...Ch. 2 - Prob. R27RQCh. 2 - Prob. P1PCh. 2 - Prob. P2PCh. 2 - Prob. P3PCh. 2 - Prob. P4PCh. 2 - Prob. P5PCh. 2 - Prob. P6PCh. 2 - Prob. P7PCh. 2 - Prob. P8PCh. 2 - Prob. P9PCh. 2 - Prob. P10PCh. 2 - Prob. P11PCh. 2 - Prob. P13PCh. 2 - Prob. P14PCh. 2 - Prob. P15PCh. 2 - Prob. P16PCh. 2 - Prob. P17PCh. 2 - Suppose you can access the caches in the local DNS...Ch. 2 - Prob. P21PCh. 2 - Prob. P22PCh. 2 - Prob. P23PCh. 2 - Prob. P25PCh. 2 - Prob. P26PCh. 2 - Prob. P27PCh. 2 - Prob. P28PCh. 2 - Prob. P29PCh. 2 - Prob. P30PCh. 2 - Prob. P31PCh. 2 - Prob. P32P
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