1. Review for Exam 4 School of Business Eastern Illinois University © Abdou Illia, Fall 2004

2. The Internet School of Business Eastern Illinois University

3. 3 The Internet addressing system n Network deliver messages based on network addresses – The Internet has two addressing systems for hosts n IP addresses. Example: 139.67.8.3 n Host names (or domain names or Unique Resource Locators). Example: eiu.edu Host

4. 4 IP Address n IP addresses – Are really strings of 32 bits (1s and 0s) n Example: 10000000101010100001000100001101 – Usually represented by four number segments separated by dots: dotted decimal notation n Example: 128.171.17.13 – Official addresses for hosts 127.18.47.145 127.47.17.47

5. 5 Assigning Parts n Most Organizations have multiple Segments within the Organizational Network n So, usually Local Part is broken in two parts – a Segment Part to represent each segment – Remaining Bits are the Host Part, designating a particular station on that segment Network PartSegment Part IP Address (32 bits total) Host Part Local Part

6. 6 IP address Place Value (2 N ) BitDecimal 1281 6400 321 1600 800 400 212 111 163 Position (N) 7 6 5 4 3 2 1 0 Binary 10100011 = Decimal 163 Note: Starts with 0

7. 7 Network classes n The value of the first octet in an IP address determines the Network class Class A Class B Class C 0.x.x.x to 127.x.x.x 128.0.x.x to 191.255.x.x 192.0.0.x to 223.255.255.x ClassAddress range 0xxx 10xx 110x Leftmost bits 8 bits 16 bits 24 bits Network Part Length Place Value (2 N ) BitDecimal 128 64 32 16 8 4 2 1 Position (N) 7 6 5 4 3 2 1 0 1) For each of the following IP addresses, give the class and the network bits. 10101010111110000101010100000001 01010100111110000101010100000001 2) To which class belong Eastern’s network? (Net. Part =139.67)

8. 8 Summary Questions 1. a) Distinguish between IP address and host name. b) Which is the official address of a host? c) Does a server host need an IP address? d) Does your home PC need an IP address when you are on the Internet? e) Does a server host need a host name? f) Does your home PC need a host name when you are on the Internet? 2. Using the conversion system on slide #10, convert the following IP address to dotted decimal notation: 10101010 11110000 11001100 01010101. (Spaces are included to facilitate reading.)

9. 9 Summary Questions 3. a) What are the three parts in IP addresses? b) What part(s) do border routers look at to determine whether the destination host is within the network or outside of it? 4. a) Who assigns the Network part? b) The Segment part? c) The Host part? 5. 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? 4. 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?

10. 10 Contoso Inc. is a small company with two departments (Marketing and Sales). In order to take advantage of the growing global market, the company decided to setup a commercial website. For that, Contoso Inc. applied for a domain name and a network part to use for assigning IP addresses to its existing server and workstations. The Registrar assigned the Network Part 137.75 to the company. As the assistant of the network administrator at Contoso Inc., you are responsible for assigning IP addresses to the company’s server and workstations. Six workstations and the server are located in the Marketing department. The other workstations are located in the Sales department. Based on your knowledge about Network parts, Segment parts and Host parts, assign IP addresses so that we can easily know the location of a computer based on its IP address. n Computer 1 located in the Marketing department: n Computer 2 located in the Sales department: n Server: n Computer 3 located in the Sales department: Note: The Network part should be same for all computer at Contoso Inc. Computers in the same department should have the same Segment part.

11. Security School of Business Eastern Illinois University

12. 12 Summary Questions n Name a few kinds of systems attacks Answer (Security, Slide #3): Denial of Service attacks, Malicious content attacks and Intercepting messages. n 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 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 sends commands to Zombie programs which execute the attacks. n Name some techniques usually used to protect a communication against Intercepting messages. Answer: Symmetric key encryption/decryption and Public key encryption/decryption

13. 13 Summary Questions n 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. n 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.

14. 14 Summary Questions 1. Briefly describe the various types of malicious content attacks Answer: See slide #6 1. What headers and messages do Packet filter firewalls examine? Answer: See slide #10 2. 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.