Transcript Introduction - Eastern Illinois University

School of Business
Eastern Illinois University
Review for Exam 4
© Abdou Illia, Spring 2006
School of Business
Eastern Illinois University
The Internet
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Host name

Host Names
eiu.edu
–
The other network addressing system on the Internet
–
Easy to remember
 microsoft.com
 eiu.edu
Two or more text “labels” separated by dots
–
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Host name

Host Names
–
eiu.edu
Like nicknames
 Not official addresses
 Each host must have an IP address
 But only some hosts have host names
 If you give it a host name, your browser must look
up IP address of host
Domain Name System (DNS)
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Domain Name System (DNS)

User’s computer sends a DNS host the target
host’s host name in a DNS Request message

DNS host returns the target host’s IP address in
DNS Response message
eiu.edu
Originating
Host
139.67.8.3
DNS
Host
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Domain Name System (DNS)

Organizations or ISPs have local DNS hosts

These hosts must know only local host names and
IP addresses

For other host names, local DNS host passes
request to another DNS host
Originating
Host
Local
DNS
Host
Remote
DNS
Host
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Domain Name System (DNS)

Remote DNS host passes information back to the
local DNS host

Local DNS host passes information back to user
PC
Originating
Host
Local
DNS
Host
Remote
DNS
Host
Domain Name System (DNS)
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Autoconfiguration

Every computer attached to the Internet is a host
–
Including desktop PCs

Every host must have an IP address

Some hosts, such as routers and webservers, get
permanent IP addresses
–
So that they can be found easily
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Autoconfiguration

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User PCs do not need permanent IP addresses
– They only need to be found within a use session
– They usually are given temporary IP addresses
each time they use the Internet
– They may get a different IP address each time
they use the Internet
Autoconfiguration

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Request-Response Cycle
–
User software requests IP address for the user PC in
Autoconfiguration Request message
–
Autoconfiguration Response message contains temporary IP address
to use in current session
Autoconfiguration

Most popular autoconfiguration protocol is
DHCP
–
–
–

Dynamic Host Configuration Protocol
Built into Windows after Win 3.1
Supplies host with temporary IP address
DHCP can give more information too
–
–
–
Usually gives IP address of a default gateway
(Microsoft terminology for router)
Can give IP address of a local DNS host
Can give other information as well
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Summary Questions
1) a) When do we need DNS? b) What information do
you send in a DNS request message? c) What
information do you receive in a DNS response
message?
2) a) What is autoconfiguration? b) What information
do we get back, at a minimum, in an
autoconfiguration response message? c) What other
information may we get back?
School of Business
Eastern Illinois University
Security
Quiz

Check Quiz 3 (Part 1) questions
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Summary Questions

Name a few kinds of systems attacks
Answer (Security, Slide #3): Denial of Service attacks, Malicious
content attacks and Intercepting messages.

Distinguish between Denial-of-Service (DoS) attack and Distributed
Denial-of-Service (DDoS) attack
Answer (Security, Slides #4, 5): In DoS attack, the attacker sends a
stream of messages or an oversized message to the victim (usually a
server) from a single computer connected to the network. In DDoS, the
attacker hacks into multiple clients and plants Zombie programs on
them. Then, he/she sends commands to Zombie programs which
execute the attacks.

Name some techniques usually used to protect a communication
against Intercepting messages.
Answer: Symmetric key encryption/decryption methods, and Public key
encryption/decryption methods
Summary Questions

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Jason sends a message to Kristin using public key encryption. (a) What
key will Jason use to encrypt the message? (b) What key will Kristin
use to decrypt the message? (c) What key will Kristin use to encrypt
the reply? (d) What key will Jason use to decrypt the reply? (e) Can the
message and reply be long messages? Explain.
Answer:
a) Jason will encrypt the message with Kristin’s public key.
b) Kristin will use her own private key to decrypt the message.
c) Kristin will use Jason’s public key to encrypt the reply.
d) Jason will use his own private key to decrypt the reply.
e) No, public key encryption can only encrypt short messages.

Does public key encryption have a problem with secure key exchange
for the public key? Explain.
Answer: There is no problem distributing the public key, because it does
not have to be distributed securely. You can even find companies’
public keys on their website.
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Summary Questions
1.
Briefly describe the various types of malicious content
attacks
Answer: See slide #6 in class notes
2.
What headers and messages do Packet filter firewalls
examine?
Answer:
3.
See slide #10 in class notes
a) What part of a packet do Application firewalls examine?
b) What do they look for?
Answer: a) Application layer messages.
b) They look for illicit content.
Network Management 2
Quiz

Check Quiz 3 (Part 2) questions
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Summary Questions (Part 1)
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1) List the main elements in centralized network
management
2) Does the Manager communicate directly with the
managed devices? Explain.
3) Explain the difference between a managed device
and objects.
4) Where is the MIB (database) stored?
Summary Questions (Part 2)
1) In Manager-Agent communications, which
device creates commands? Responses? Traps?
2) Explain the two types of commands.
3) What is a trap?
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