Fundamentals of the Internet 2009/ Explain meaning the following networking terminologies:

Transcription

1 Fundamentals of Internet Tutorial Questions (2009) 1. Explain meaning the following networking terminologies: Client/server networking, Coax, twisted pair, protocol, Bit, Byte, Kbps, KBps, MB, KB, MBps, Mbps, MHz, GHz, CCNA, CCNP, CCIE, MAC address, Port number, ARP, RARP, HTTP, HTML, XML and URL. Coaxial cable, or coax, is a cable with an inner conductor surrounded by a tubular insulating layer typically of a flexible material with a high dielectric constant Kbps k bit/s KBps k Byte/s MAC address - Media Access Control address CCNA- Cisco Certified Network Associate CCNP- Cisco Certified Network Professional CCIE- Cisco Certified Internetwork Expert 2. Learn the HTML tags to produce table, number and non-numbered lists, horizontal ruler, link to in a webpage to other webpage, tag to insert image in a webpage etc. 3. How many types of variable does Perl have? What are they and what kind of values do they store? Explain, giving an example in each case. 4. What is Environment variable? How to write a perl code to print environment variable? Why you should always to put #!/usr/bin/perl to the first line of your perl program? 5. The 4 layers of TCP/IP are Application Layer, Transport Layer, Internet Layer and Link Layer. Clearly outline the 4 layers of TCP/IP with function and purpose of each layer showing the type of services that runs on each one of them. TCP/IP - (Transmission Control Protocol / Internet Protocol) The protocol that computers and network devices use to communicate over the Internet. Application Layer: provides a wide range of services to network users mainly in the form of applications. (e.g. FTP, Telnet, SMTP) Transport Layer: provides an end-to-end data deliveryservice that application processes use to exchange messages over the Internet. (e.g. TCP or UDP) Internet Layer: routing and relaying functions for carrying packets of data from a source system to a destination system through an internet. (IP Addressing system) Link Layer: Is a hardware dependent (e.g. Ethernet, NIC cards, Router) layer that handles physical communication using a standard interface from and to the Internet layer of TCP/IP.

2 6. A Router is a central switching device in a packet switched network that directs and controls (routes) the flow of data. A traditional router routes packets within a single address and a NAT router directs datagrams between different address realms. What is NAT and how does it works? 7. What are the main differences between circuits switching and packet switching?

3 8. What and how does public key cryptography works on the Internet. Draw a simple diagram to show how the message will be encrypted and send over the Internet. public key algorithm based on mathematical functions. uses asymmetric cryptography involving use of 2 separate keys there are 6 ingredients; 1. plaintext- input(readable message or data) that is fed into the algorithm. 2. encryption algorithm- perform various transformations of the plaintext. 3. public and private key- pair of keys selected and one is used for encryption and the other for decryption. 4. Ciphertext- the scrambled message produced as output. Depends on plaintext and the keys. Two different keys will produce two different cipher text. 5. decryption algorithm- accepts ciphertext and matching key and produce original plaintext that was given initially. essential steps that will be taken: 1. User generating pair of keys used for encryption and decryption

4 2. One key placed in public register/accessible file. The other key is kept private. 3. If A wishes to send message to B, A encrypts message using B s public key. 4. B upon receiving message, decrypts using own private key 5. All users have access to public key but private key generated locally. sample public key cryptography 9. The IP addressing system is divided into class A,B,C,D and E. Each class uses the 4octet numbers ranging from 0 to 255. Show how IP address are seen by the computer/or network device and define the classification of each of the class of the addressing system.

5 10. What is the Domain Name System and what services does it provide? The Domain Name System (DNS) helps users to find their way around the Internet. Every computer on the Internet has a unique address just like a telephone number which is like a complicated string of numbers. Its called "IP address" (Internet Protocol). But hard to remember everyone's IP address. DNS makes it easier by allowing a familiar string of letters (the "domain name") to be used instead of the arcane IP address. Instead of typing , you can type instead. It is a "mnemonic" device that makes addresses easier to remember. Translating the name into the IP address is called "resolving the domain name. The goal of the DNS is for any Internet user any place in the world to reach a specific website IP address by entering its domain name. 11. Explain the purpose and functionalities of a mailing list. a. collection of names and addresses used by an individual or an organization to send material to multiple recipients. b. The term is often extended to include the people subscribed to such a list, so the group of subscribers are referred to as "the mailing list", or simply "the list". c. At least two quite different types of mailing lists can be defined: i. the first one is closer to the literal sense, where a "mailing list" of people is used as a recipient for newsletters, periodicals or advertising. Traditionally this was done through the postal system, but with the rise of , the electronic mailing list became popular. ii. When similar or identical material is sent out to all subscribers on a mailing-list, it is often referred to as a mailshot. d. Mailing lists are often rented or sold. e. If rented the renter agrees to use the mailing list foronly the agreed upon times. f. The mailing list owner typically enforces this by "salting" the mailing list with fake addresses and creates new salts for each time the list is rented. g. Unscrupulous renters may attempt to bypass salts by renting several lists and merging the lists to find the common, valid addresses. h. Mailing list brokers exist to help organisations rent their lists. For some organizations such as specialized niche publications or charitable groups, their client list may be one of their most valuable assets and mailing list brokers help them maximise the value of their lists. 12. Explain the terms: USENET, UUCP

6 13. Using suitable diagrams, describe how the system works step by step. From the above diagram, the system works in the following procedure: Step A: Sender creates and sends through their Mail User Agent (MUA) Step B: Sender s MUA transfer the to the Mail Delivery Agent (MDA/MTA) Step C: MDA/MTA accepts the then routes it to local mailboxes or forwards it if it isn t a local address. Step D: Network cloud or means it enters ISP or the Internet. The network cloud includes mail servers, DNS servers, routers Step E: (Step A,B,C is reversed) upon arrival of on client side.

7 14. How many protocols involved in the current system over Internet? Name these protocols and explain their uses. Nowadays, the system needs two types of protocols, the retrieval protocols and mail transfer protocols. The retrieval protocols deal with the communication between mail user agent (MUA) and mail delivery agent (MDA). These include POP3 and IMAP protocols. POP3 stands for Post Office Protocols, version 3. Functions of POP3 include: Send / Retrieve mail messages from the local MTA Authentication Update mailbox at local MTA. POP protocol is a very simple protocol. The POP client makes a TCP connection to the POP Mail Server on port 110. The client sends ASCII commands to the Mail Server to send / retrieve / delete s. IMAP stands for Internet Message Access Protocol (IMAP). IMAP uses TCP port 143. IMAP has greater functionality than POP It provides better authentication. Users can create / delete and manage multiple mailboxes It allows users to manipulate their mail more easily. It can search / find messages by subject, message body or keywords. It allows filtering of and can apply operations to a selection of s. It allows s to be stored on the Mail Server instead of downloading them to the users computer. This allows a user to access their from any computer that can make a TCP connection to the Mail Server. The transfer protocols include SMTP and its extension MIME. The SMTP stands for Simple Mail Transfer Protocols. It relays s between two MTAs (mail servers). MIME stands for Multipurpose Internet Mail Extension. It s a extension protocols to POP, IMAP and SMTP. It allows handling various attachments like video, audio, etc. to . MIME is not just restricted to it is now used in HTTP to deliver audio, video, etc 15. Write short notes to explain each of the below terms: a) Computer virus and Smurf attack(d-o-s) b) Firewall c) Cookies c) (D-o-S)

8 A computer virus is a program with the characteristic feature of being able to generate copies of itself, and thereby spread. Additionally most computer viruses have a destructive payload that is activated under certain conditions. Example: The Chernobyl virus overwrites the beginning of the hard disk on certain dates. In D-o-S, a large amount of ICMP echo (ping) traffic is sent at IP broadcast addresses(all having a spoofed source address of a victim) If the routing device delivering traffic to those broadcast addresses performs the IP broadcast to layer 2 broadcast function, most hosts on that IP network will take the ICMP echo request and reply to it with an echo reply each This will multiply the traffic by the number of hosts responding. On a multiaccess broadcast network, there could potentially be hundreds of machines to reply to each packet. a) Firewall A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If an incoming packet of information is flagged by the filters, it is not allowed through. Firewalls use one or more of three methods to control traffic flowing in and out of the network: o Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. o Packets that make it through the filters are sent to the requesting system and all others are discarded. o Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa. o Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. o Information travelling from inside the firewall to the outside is monitored for specific defining characteristics, and then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded. b) Cookies are pieces of information generated by a Web server and stored in the user's computer, ready for future access. are embedded in the HTML information flowing back and forth between the user's computer and the servers. Cookies were implemented to allow user-side customization of Web information. For example, cookies are used to personalize Web search engines, to allow users to participate in WWW-wide contests(but only once!), and to store shopping lists of items a user has selected while browsing through a virtual shopping mall.

9 Essentially, cookies make use of user-specific information transmitted by the Web server onto the user's computer so that the information might be available for later access by itself or other servers. In most cases, not only does the storage of personal information into a cookie go unnoticed, so does access to it. Web servers automatically gain access to relevant cookies whenever the user establishes a connection to them, usually in the form of Web requests.