Networking Fundamentals Review. Networking Evolution. Network: Two or more connected computers that share data Paradigms: Client/server model Mainframe model Peer to peer Web-based networking
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Networking Evolution • Network: • Two or more connected computers that share data • Paradigms: • Client/server model • Mainframe model • Peer to peer • Web-based networking • Sneakernet:The transfer of files from one computer to another using a floppy disk or other removable medium
Networking Categories • Two basic categories: • Server-based • Peer-to-peer • Enterprise networks • Combine peer-to-peer and server-based
Layers of the OSI/RM • Application All • Presentation People • Session Seem • Transport To • Network Need • Data link Data • Physical Processing
Application Layer • User interface • Supports file transfer • Network management • Accepts requests and passes them down to the presentation layer
Presentation Layer • Converts text from what is viewable to the user to what is understandable to the computer • Passes data to session layer
Session Layer • Establishes, manages, and terminates connections between cooperating applications • Adds traffic flow information
Transport Layer • Reliable, transparent transport between end points • Supports end to end error recovery and flow control • Connection-oriented protocols reside at this layer
Network Layer • Responsible for forwarding and routing datagrams • Connectionless protocols reside at this layer
Data Link Layer • Provides reliable data transfer across the physical link • Frames are transmitted with the necessary synchronization error control and flow control • Prepares information so it can be sent to the physical wire
Physical Layer • Concerned with the transmission of unstructured bit stream over a physical link • Responsible for the mechanical, electrical, and procedural characteristics to establish, maintain, and deactivate the flow of bits
Major Networking Protocols • Connection-oriented (stateful) • Connectionless (stateless) • Routable – Most protocols are routable • Nonroutable • NetBios • NetBeui • LAT • DLC
TCP/IP • Default protocol for the following network operating systems: • Windows 2000 • Windows NT 4.0 • UNIX • NetWare 5 … plus the Internet! • Computers are each identified with an IP address and subnet mask
IPX/SPX • IPX is responsible for forwarding packets to sockets • SPX ensures reliable data delivery and manages sessions • Must identify a frame type during setup
NetBEUI • Non-routable • Fast • Easiest to configure and maintain • Low overhead
AppleTalk • Used only on Apple Macintosh networks • Divides groups of computers into zones
Repeaters • Amplifies electronic signal • Strengthens signal by re-transmitting it when segment approaches its maximum length
Hubs • Concentration point of network • Used with a star configuration
Bridges • Operates on the data link layer • Reduce network traffic by dividing the network into two segments • Recognize mac addresses rather than IP addresses • Can connect two different topologies
Routers • Operates on the network layer • Forwards or route data according to routing tables • Determine IP address needed and then most efficient route • Conserves network bandwidth by reducing broadcasting
Switches • Can operate at the data link and network layers • Directs the flow of information from one node to another. • Faster because it give each sender/receiver the entire bandwidth of a line instead of sharing
Gateways • Can operate at any level of the OSI model • Protocol converter – Appletalk to TCP/IP
CSU/DSU • Channel Service Unit/Data Service Unit • Operates at the physical layer • Terminates physical connections • Used for bringing T1 lines into a building
Modems • Uses POTS phone line to connect to internet • Can dial RAS connection directly to another computer
Modem Initialization Commands AT – Precedes most commands ATDT – Dials the number ATA – Answers an incoming call manually ATH0 – Tells modem to hang up AT&F – Resets the modem to factory defaults ATZ – Resets modem to power up defaults , - Pause *70 or 1170 – Turns off call waiting
Transmission Media • Twisted pair cable • Coaxial cable • Fiber optic cable • Wireless media
Transmission Media • Twisted pair cable • UTP and STP • 100 meter length maximum • Twisted pair or 8 wires in 4 pairs, RJ-45 connectors • Category 3 – Ethernet 10BASE-T, 10mbps nics and hubs (16mbps maximum) • Category 4 – Used for token ring, generally at 16mbps (20mbps maximum) • Category 5 – Ethernet 100BASE-T, 100mbps nics and hubs (155mbps maximum)
Transmission Media (cont.) • Coaxial cable • No concentrator is needed • Requires a terminator at each end • Thicknet - 500 meters, .5” (10BASE5) • Thinnet - 185 meters, .25” (10BASE2) • RG-58 cable, BNC connectors • Up to 255 devices can be attached to a single segment
Transmission Media (cont.) • Fiber optic cable • Two strands of optical fiber, one sends, one receives, with pulses of light • FDDI and ATM technologies • 622 mbps (100-1,000mbps), 2,000 meters • Expensive and difficult to install • Very secure • No EMI • 100BASE-FX • Wireless media
Port Numbers • Well-known port numbers • 25 – SMTP • 20, 21 – FTP • 110 – POP • 53 – DNS • 80 – HTTP • Numbers can also be assigned for security purposes
Internet Addressing • Internet addresses are divided into the following parts: • Network • Host • Four fields separated by periods are a common notation for specifying addresses: • field1.field2.field3.field4 (222.41.1.25)
1 = On 0 = Off IP Address Fields • Contain eight bits per field • Range from 0 to 255 decimal field1.field2.field3.field4 1 1 1 1 1 1 1 1 = 8 128 64 32 16 8 4 2 1 = 255
Internet Address Classes • Class A – 1-126 0 • Class B – 128-191 10 • Class C – 192-223 110 • Class D – 224-239 1110 • Class E – 240-247 11110
Reserved (LAN) IP Addressing • 10.0.0.0 through 10.255.255.255 • 172.16.0.0 through 172.31.255.255 • 192.168.0.0 through 192.168.255.255
Subnetworks • Subnet masks – used to distinguish network and host portions of addresses • efault subnet masks • Class A 255.0.0.0 • Class B 255.255.0.0 • Class C 255.255.255.0 • IPv6 – 128 bit address instead of 32 bit
Classifying Hackers • Casual attacker - 99.5% • Determined attacker - usually on ideological grounds, or a disgruntled employee
Types of Attacks • Spoofing (masquerade) attacks - alters ip so it looks like it came from a trusted network • Man-in-the-middle (hijacking) attacks - capture packets sent between two hosts • Denial-of-service attacks - uses up all the system resources and crashes the system, usually with ping requests • Insider attacks – eavesdropping and snooping for information • Brute-force attacks - repeated logon attempts with a dictionary
Types of Attacks • Trapdoor attacks - diagnostics programs can view and possibly execute system applications • Replay attacks - altered header info on packets to gain entrance to system • Trojan horse attacks – files placed on system by user that believes the program is a valid program, user executes • Social-engineering attacks – users tricked into giving out their personal information (this info is then used to crack passwords) • Front Door - stolen user name and password
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