Networking Essantial


Networking Essentials exam prep.

1. IRQ (Interrupt Requests)
IRQ 1         Keyboard 
IRQ 2(9)    Video Card 
IRQ 3         Com2, Com4 
IRQ 4         Com1, Com3 
IRQ 5         Available (Normally LPT2 or sound card ) 
IRQ 6         Floppy Disk Controller 
IRQ 7         Parallel Port (LPT1) 
IRQ 8         Real-time clock 
IRQ 9         Redirected IRQ2 
IRQ 10       Available 
IRQ 11       Available 
IRQ 12       PS/2 Mouse 
IRQ 13       Math Coprocessor 
IRQ 14       Hard Disk Controller 
IRQ 15       Available 
 
2. Standard Topologies 
Bus             - A single cable (trunk) that connects all computers in a single line. 
Star            - Computers connect to a centralized hub via cable segments. 
Ring           - Connects all computers on a single cable. Ends are not terminated, but form a full loop connecting the last computer to the first computer. 
Mesh          - Commonly used in WAN configurations. Routers are connected to multiple links for redundancy and to give the ability to determine the quickest route to a destination. 
 
3. Access Methods 
CSMA/CD                     - Collision Detection; listens to cable prior to sending data. (Ethernet)
CSMA/CA                     - Collision Avoidance; Announces intention to send data. (AppleTalk)
Token-Passing              - Token revolves around ring, computer which has token is permitted to data. (Token Ring)
One device designated media administrator. Secondary device waits to be polled by primary device to check if it has data to be sent.
 
4. IBM Cabling System
Thinnet Coaxial - .25 inches thick, carries signal 185 meters. Known as RG-58 family, and has a 50 ohm impedance. 
RG-58 /U                       - Solid Copper Core 
RG-58 A/U                    - Stranded Wire Core 
RG-58 C/U                    - Military Specification of RG-58 A/U 
RG-59                             - Broadband transmission (Television Cable) 
RG-62                             - ArcNet Network Cable 
- When troubleshooting thinnet coaxial cable, the cable terminator must read 50 ohms, and the cable and connector must measure infinite.
Thicknet Coaxial         - .5 inches thick, carries signal 500 meters. A transceiver (Vampire Tap) is used to make a physical connection with the Thicknet core. 
Unshielded Twisted Pair - Twisted pair wiring, carries signal 100 meters. Is susceptible to crosstalk. 
Shielded Twisted Pair - Twisted pair wiring, carries signal 100 meters. Has foil or braided jacket around wiring to help reduce crosstalk and to prevent electromagnetic interference. 
Attenuation                   - The degrading of a signal as it travels farther from its origination. 
Crosstalk                        - Signal overflow from one wire to another adjacent wire. 
Jitter            - Instability in a signal wave. Caused by signal interference or an unbalanced FDDI ring or Token Ring. 
 
5. UTP/STP Category Speeds 
Cat 2          - 4 mbps 
Cat 3          - 10 mbps 
Cat 4          - 16 mbps 
Cat 5          - 100 mbps 
Fiber-Optic - Carries light pulse signals through glass core at speeds of between 100 Mbps - 200,000 Mbps.
6. Ethernet Specifications 
Type                               Cable types                                        Connection Type         Max Length 
10Base2                         - RG-58 thinnet coaxial cable        BNC T Connector        185 meters (607 ft) 
10Base5                         - Thicknet coaxial cable                  DIX/AUI                        500 meters (1640 ft) 
10BaseT                        - Category 3, 4, or 5 UTP cable      RJ-45                              100 meters (328 ft) 
100BaseT                      - Category 5 UTP cable                   RJ-45                              100 meters (328 ft) 
 
7. Signal Transmissions 
Baseband                      - Uses digital signaling over a single frequency. Transmits bi-directionally. 
Broadband                   - Uses analog signaling over a range of frequencies. Transmits unidirectionally and uses amplifiers for signal regeneration. 
 
8.  OSI Model 
Application Layer      - Allows applications to use the network. Handles network access, flow control and error recovery. 
Presentation Layer    - Translates data into a form usable by the application layer. The redirector operates here. Responsible for protocol conversion, translating and encrypting data, and managing data compression. 
Session Layer              - Allows applications on connecting systems to establish a session. Provides synchronization between communicating computers. 
Transport Layer         - Responsible for packet handling. Ensures error-free delivery. Repackages messages into smaller packets, and handles error handling. 
Network Layer            - Translates system names into addresses. Responsible for addressing, determining routes for sending, managing network traffic problems, packet switching, routing, data congestion, and reassembling data. 
Data Link Layer         - Sends data from network layer to physical layer. Manages physical layer communications between connecting systems. 
                    LLC           - (802.2) Manages link control and defines SAP's (Service Access Points). 
                    MAC          - (802.3, 802.4, 802.5, 802.12) Communicates with adapter card. 
Physical Layer            - Transmits data over a physical medium. Defines cables, cards, and physical aspects. 
 
OSI layer  Protocols residing here
Application                    SMB, NCP
Presentation                  NCP
Session                           None
Transport                       TCP, SPX, NWLink, NetBEUI
Network                         IP, IPX, NetBEUI, DLC, DecNET
Data Link                      None
Physical                          None
 
IEEE 802 Specifications 
802.1          Internetworking 
802.2          LLC (Logical Link Control) 
802.3          CSMA/CD - Ethernet 
802.4          Token Bus LAN 
802.5          Token Ring LAN 
802.6          MAN (Metropolitan Area Network) 
802.7          Broadband Technical Advisory Group 
802.8          Fiber-Optic Technical Advisory Group 
802.9          Integrated Voice/Data Networks 
802.10        Network Security 
802.11        Wireless Networks 
802.12        Demand Priority Access LAN, 100 Base VG - AnyLAN 
 
9. LAN Enhancement Components 
Repeater   - regenerates  signals for retransmission. Moves packets from one physical media to another. Will pass broadcast storms. Cannot connect different network topologies or access methods. 
Bridges      - are used to segment networks. They forward packets based on address of destination node. Uses RAM to build a routing table based on hardware addresses. Will connect dissimilar network topologies. Will forward all protocols. Regenerates the signal at the packet level. 
Remote Bridge - Same as bridge, but used for telephone communications. Uses STA (Spanning Tree Algorithm).  
Routes        - packets across multiple networks. Uses RAM to build a routing table based on network addresses (i.e. TCP address). Shares status and routing information to other routers to provide better traffic management and bypass slow connections. Will not pass broadcast traffic. Are slower than bridges due to complex functions. Strips off Data Link Layer source and destination addresses and then recreates them for packets. Routers can accommodate multiple active paths between LAN segments. Will not pass unroutable protocols. 
Brouter     - Will act as a router for specified protocols and as a bridge for other specified protocols.  
Gateway    - Used for communications between different NOS's (i.e. Windows NT and IBM SNA). Takes the packet, strips off the old protocol and repackages it for the receiving network. 
Multiplexer Device - that can divide transmissions into two or more channels. 
Switches    - Hub with bridging capabilities. Switch filters traffic through MAC addresses. Creates sessions on ports within the hub. Used when upgrading to 100mb Fast Ethernet. 
Repeater                        Physical 
Bridge                             Data Link (MAC Sublayer) 
Remote Bridge              Data Link (MAC Sublayer) 
Router                            Network 
Brouter                           Data Link and Network 
Gateway                        Transport, Session, Presentation and Application 
Multiplexer                    Physical 
Switch                            Data Link 
Spanning Tree Algorithm - was developed for bridges to determine the most efficient network in path when there are multiple paths to choose from. 
Multiplexing - Several signals from different sources are collected into the component and are fed into one cable for transmission.
 
9a. Protocols 
Routable   - TCP/IP, IPX/SPX, OSI, AppleTalk, DecNET, XNS. Non-routable - NetBEUI, DLC, LAT. 
NetBEUI   - Microsoft protocol designed for small LANs; non-routable. Not compatible with UNIX networks. 
IPX/SPX   - Fast protocol for small and large Novell networks; is routable. Also known in NT as NWLink. 
TCP/IP      - Internet protocol; is routable. Used by UNIX networks. 
DecNET    - Defines communications over FDDI MANs; is routable. 
AppleTalk - Apple protocol designed for small LAN file and print sharing; is routable. 
RIP (Routing Information Protocol) - Routers use this to communicate with each other to determine the least busy and shortest network routes. 
NDIS (Microsoft) and ODI (Novell) are used to bind multiple protocols to a network adapter.
SLIP (Serial Line IP)   - Provides dial-up communications, but is unable to simultaneously transfer multiple protocols. 
PPP (Point-to-Point Protocol) - Performs dynamic IP addressing, multi-protocol support, password login and error control. 
Common TCP/IP problems are caused by incorrect subnet masks and default gateways.
Incorrect frame types will cause problems between two systems using IPX/SPX.
 
10. Computer Name Resolution 
DNS (Domain Name Services) - Used to resolve DNS host name to an IP address. 
WINS (Windows Internet Naming Service) - Used to resolve NetBIOS computer name to an IP address. 
HOSTS - File which contains mappings between DNS host names and their IP addresses. 
LMHOSTS - File which contains mappings between NetBIOS computer names and their IP addresses. 
Packet Switching - Packets are relayed across network along the best route available. 
Beaconing - Computers are used to detect network faults, then transmit the fault signal to the server. 
Packet Switching Networks 
Type           Function
X.25           Designed to connect remote terminals to mainframe host systems. Is very slow due to constant error-checking.
Frame Relay                Point-to-point system which uses digital leased lines. Will provide bandwidth as needed. Requires frame relay capable bridge or router for transmission.
ATM          Advanced implementation of packet switching. Transmits at speeds of 155Mbps to 622Mbps with capabilities of higher speeds. Transmits data in 53 byte (48 application, 5 header) cells. Uses switches as multiplexers to permit several computers to simultaneously transmit data on a network. Great for voice and video communications.
ISDN          Transmits at 128k/sec. Has three data channels - 2 B channels @ 64k/sec & 1 D channel @ 16k/sec. The B channels carry data while the D channel performs link management and signaling.
FDDI          100 Mbps token-passing ring network which uses fiber-optic media. Uses a dual-ring topology for redundancy and in case of ring failure. Each ring is capable of connecting 500 computers over 100 kilometers (62 miles). Can be used as a network backbone. Uses beaconing for ring troubleshooting.
Security levels 
Share-level security - Used in Windows 95 to share resources. A password is needed to access the resource. 
User-level security - Used in Windows NT to share resources. When you attempt to access a shared resource, the server will make sure your user account has been authorized to access the resource. 
 
11. Network Diagnostic Tools 
Tool                                                     Function
Digital Volt Meters (DVM)           Measures voltage passing through a resistance. Primarily used for network cable troubleshooting.
Time-Domain Reflectors (TDRs)                     Sends sonar-like pulses to look for breaks, shorts or crimps in cables. Can locate a break within a few feet of actual fault.
Oscilloscope                                     Measures amount of signal voltage per unit of time. Displays crimps, shorts, opens, etc.
Network Monitor                            Examines packet types, errors and traffic to and from each computer on a network.
Protocol Analyzer                          Look inside the packet to determine cause of problem. Contains built in Time-Domain Reflector.                                 Gives insights to many problems including connection errors, bottlenecks, traffic problems, protocol problems, etc.
 
12. Multiple Disk Sets 
Fault Tolerant Systems protect data by duplicating data or by placing data in different physical sources. 
RAID                              Function
Level 0 
Disk Striping                  -Divides data into 64k blocks and spreads it equally among all disks in the array. Is not fault tolerant.
Level 1 
Disk Mirroring               -Duplicates a partition on another physical disk.
Level 1 
Disk Duplexing             -Duplicates a partition on another physical disk that is connected to another Hard Drive Controller.
Level 2 
Disk Striping w/ECC    -Data blocks are broken up and distributed across all drives in array with error checking.
Level 3 
Disk Striping w/ ECC stored as parity    -Data blocks are broken up and distributed across all drives in array with one drive dedicated to storing parity data.
Level 4 
Disk Striping with large blocks       -Complete blocks of data are distributed across all drives in the array.
Level 5 
Disk Striping with parity                  -Distributes data and parity information across all disks in the array. The data and the and parity information are arranged so they are always on separate disks. A parity stripe block exists for each row across the disk. The parity stripe is used for disk reconstruction in case of a failed disk. Supports a minimum of three disks and a maximum of thirty-two disks.
Windows NT supports RAID Levels 0, 1, and 5.
Sector Sparing - Automatically adds sector-recovery capabilities to the files system while the computer is running. Available when using RAID methods. Only available with SCSI drives. 
 
Upgrading the network 
To upgrade a network to 100 mbps Ethernet, you must perform the following:
-  Upgrade all hubs to switches or 100 mbps hubs. 
-  Upgrade the wiring to CAT 5 UTP/STP. 
-  Upgrade all network cards to 100 mbps. 



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