Review for Exam 4The InternetThe Internet addressing systemIP AddressAssigning PartsIP addressNetwork classesSummary QuestionsSlide 9Slide 10SecuritySlide 12Slide 13Slide 14Review for Exam 4School of BusinessEastern Illinois University © Abdou Illia, Fall 2004The InternetSchool of BusinessEastern Illinois University3The Internet addressing systemNetwork deliver messages based on network addresses–The Internet has two addressing systems for hostsIP addresses. Example: 139.67.8.3Host names (or domain names or Unique Resource Locators). Example: eiu.eduHostHost4IP AddressIP addresses–Are really strings of 32 bits (1s and 0s)Example: 10000000101010100001000100001101–Usually represented by four number segments separated by dots: dotted decimal notationExample: 128.171.17.13–Official addresses for hosts127.18.47.145127.47.17.475Assigning PartsMost Organizations have multiple Segments within the Organizational Network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 segmentNetwork Part Segment PartIP Address (32 bits total)Host PartLocal Part6IP addressPlace Value(2N)Bit Decimal128 1 12864 0 032 1 3216 0 08 0 04 0 02 1 21 1 1163Position(N)76543210Binary10100011=Decimal163Note: Starts with 07Network classesThe value of the first octet in an IP address determines the Network classClass AClass BClass C0.x.x.x to 127.x.x.x128.0.x.x to 191.255.x.x192.0.0.x to 223.255.255.xClass Address range0xxx10xx110xLeftmost bits8 bits16 bits24 bitsNetwork Part LengthPlace Value(2N)Bit Decimal128 64 32 16 8 4 2 1 Position(N)765432101) For each of the following IP addresses, give the class and the network bits.10101010111110000101010100000001010101001111100001010101000000012) To which class belong Eastern’s network? (Net. Part =139.67)8Summary Questions1. 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.)9Summary Questions3. 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?10Contoso 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.Computer 1 located in the Marketing department:Computer 2 located in the Sales department:Server: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.SecuritySchool of BusinessEastern Illinois University12Summary QuestionsName a few kinds of systems attacksAnswer (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) attackAnswer (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.Name some techniques usually used to protect a communication against Intercepting messages. Answer: Symmetric key encryption/decryption and Public key encryption/decryption13Summary Questions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.14Summary Questions1. Briefly describe the various types of malicious content attacksAnswer: See slide #61. What headers and messages do Packet filter firewalls examine? Answer: See slide #102. 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