::Network Plus Certification Exam::
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The CompTIA Network+ Exam certifies that the
successful candidates knows the layers of the OSI model,
can describe the features and functions of network
components and has the skills needed to install,
configure, and troubleshoot basic networking hardware
peripherals and protocols. A typical candidate should
have A+ certification or equivalent knowledge, but A+
certification is not required. In addition to A+
certification level knowledge, candidates are encouraged
to have at least 9 months of experience in network
support or administration.
It also includes discussion on new technologies such
as wireless networking and gigabit Ethernet. The scope
of networking systems are broadened somewhat placing an
increased emphasis on Linux/Unix, Windows 9x, Windows
NT, Windows 2000 and including AppleTalk as a network
protocol. There is also more of an emphasis on hands-on
experience knowledge needed in the areas of network
implementation and network support including
troubleshooting scenarios. This study guide gives you an
overview what you needs to pass Network+ Exam.
What is a Computer Network?
A network is any collection of independent computers
that communicate with one another over a shared network
medium.A computer network is a collection of two or more
connected computers. When these computers are joined in
a network, people can share files and peripherals such
as modems, printers, tape backup drives, or CD-ROM
drives. When networks at multiple locations are
connected using services available from phone companies,
people can send e-mail, share links to the global
Internet, or conduct videoconferences in real time with
other remote users. As companies rely on applications
like electronic mail and database management for core
business operations, computer networking becomes
increasingly more important.
Types of Networks
Peer to Peer
A peer to peer network is one in which lacks a dedicated
server and every computer acts as both a client and a
server. This is a good networking solution when there
are 10 or less users that are in close proximity to each
other. A peer to peer network can be a security
nightmare, because the people setting permissions for
shared resources will be computer idiots and the right
people will never have access to the right resources.
Thus is only recommended in situations where security is
not an issue.
This type of network is designed to support a large
Number of users and uses dedicated server/s to
accomplish this. Clients log on to the server/s in order
to run applications or obtain files. Security and
permissions can be managed by 1 or more administrators
which cuts down on the aforementioned computer
illiterates from medling with things that they shouldn't
be. This type of network also allows for convenient
backup services, reduces network traffic and provides a
host of other services that come with the network
operating system (NOS).
This is also a client/server based model that is most
often seen in UNIX environments, but the clients are
"dumb terminals". This means that the client may not
have a floppy drive, hard disk or CDROM and all
applications and processing occur on the server/s. As
you can imagine, this requires fast and damn expensive
server/s. Security is very high on this type of network,
although a similar level of security can be achieved
using an NT server and setting appropriate permissions.
Network Categorization w.r.t Distance
LANs (Local Area Networks)
A network is any collection of independent computers
that communicate with one another over a shared network
medium. LANs are networks usually confined to a
geographic area, such as a single building or a college
campus. LANs can be small, linking as few as three
computers, but often link hundreds of computers used by
thousands of people. The development of standard
networking protocols and media has resulted in worldwide
proliferation of LANs throughout business and
MANs (Metropolitan area Networks)
They refers to a network of computers with in a City.
WANs (Wide Area Networks)
Wide area networking combines multiple LANs that are
geographically separate. This is accomplished by
connecting the different LANs using services such as
dedicated leased phone lines, dial-up phone lines (both
synchronous and asynchronous), satellite links, and data
packet carrier services. Wide area networking can be as
simple as a modem and remote access server for employees
to dial into, or it can be as complex as hundreds of
branch offices globally linked using special routing
protocols and filters to minimize the expense of sending
data sent over vast distances.
The Internet is a system of linked networks that are
worldwide in scope and facilitate data communication
services such as remote login, file transfer, electronic
mail, the World Wide Web and newsgroups.
With the meteoric rise in demand for connectivity,
the Internet has become a communications highway for
millions of users. The Internet was initially restricted
to military and academic institutions, but now it is a
full-fledged conduit for any and all forms of
information and commerce. Internet websites now provide
personal, educational, political and economic resources
to every corner of the planet.
Specialized Types of Networks
With the advancements made in browser-based software for
the Internet, many private organizations are
implementing intranets. An intranet is a private network
utilizing Internet-type tools, but available only within
that organization. For large organizations, an intranet
provides an easy access mode to corporate information
VPN (Virtual Private Network)
VPN uses a technique known as tunneling to transfer data
securely on the Internet to a remote access server on
your workplace network. Using a VPN helps you save money
by using the public Internet instead of making
long-distance phone calls to connect securely with your
private network. There are two ways to create a VPN
connection, by dialing an Internet service provider
(ISP), or connecting directly to Internet.
What is a Network topology?
A network topology is the geometric arrangement of nodes
and cable links in a LAN There are 4 basic topologies
- Bus consists of a single linear cable called a
- Data is sent to all computers on the trunk. Each
computer examines EVERY packet on the wire to
determine who the packet is for and accepts only
messages addressed to them.
- Bus is a passive topology.
- Performance degrades as more computers are added
to the bus.
- Signal bounce is eliminated by a terminator at
each end of the bus.
- Barrel connectors can be used to lengthen cable.
- Repeaters can be used to regenerate signals.
- Usually uses Thinnet or Thicknet both of these
require 50 ohm terminator
- Good for a temporary, small (fewer than 10
- Its difficult to isolate malfunctions and if the
backbone goes down, the entire network goes down.
- Computers are connected by cable segments to a
- Signal travels through the hub to all other
- Requires more cable.
- If hub goes down, entire network goes down.
- If a computer goes down, the network functions
- Most scalable and reconfigurable of all
- Computers are connected on a single circle of
- Usually seen in a Token Ring or FDDI (fiber
- Each computer acts as a repeater and keeps the
signal strong => no need for repeaters on a ring
- No termination required => because its a ring
- Token passing is used in Token Ring networks.
The token is passed from one computer to the next,
only the computer with the token can transmit. The
receiving computer strips the data from the token
and sends the token back to the sending computer
with an acknowledgment. After verification, the
token is regenerated. relatively easy to install,
requiring ;minimal hardware.
- The mesh topology connects each computer on the
network to the others
- Meshes use a significantly larger amount of
network cabling than do the other network
topologies, which makes it more expensive.
- The mesh topology is highly fault tolerant.
- Every computer has multiple possible connection
paths to the other com-puters on the network, so a
single cable break will not stop network
communications between any two computers.
Primary Cable Types
- Consists of a solid or stranded copper core
surrounded by insulation, a braided shield and an
- Braided shield prevents noise and crosstalk.
- More resistant to interference and attenuation
than twisted pair cabling.
- Both thin and thick cables can use BNC cable
connectors, BNC barrel connectors BNC T connectors
- Can transmit data, voice and video.
- Offers moderate security ----> better than
Thinnet - RG-58 cable
- 0.25" thick.
- Uses BNC twist connector, BNC barrel connectors
BNC T connectors 50 ohm terminators
- Can carry signals 185 meters or 607 feet.
- Each cable must have a terminator whose
impedance matches the cable type
Thicknet - RG-8 and RG-11 coaxial cable
- 0.5" thick
- used for 10Base5 networks, linear bus topology
- Transmits at 10 Mbps
- Uses DIX or AUI (Attachment Unit Interface)
connector - also known as DB-15 connector to connect
to external transceivers.
- Can carry signals 500 meters or 1640 feet.
- much less flexible and far more bulky and harder
to install than thinnet
- better security than thinnet
- better resistance to electrical interference
- MORE expensive than thinnet.
- Consists of two insulated copper wires twisted
around each other.
- Twisting cancels out electrical noise from
adjacent pairs (crosstalk) and external sources.
- Uses RJ-45 telephone-type connectors (larger
than telephone and consists of eight wires vs.
Telephone's 4 wires).
- Generally inexpensive.
- Easy to install
Unshielded Twisted Pair (UTP)
- Maximum cable length is 100 meters or 328 feet
1.Cat 1 Voice grade telephone cable.
2.Cat 2 Data grade up to 4 Mbps, four twisted pairs.
Category 3 and above is needed for Ethernet
networks. Cat 3, 4, and 5 use RJ-45 connectors
1.Cat 3 Data grade up to 10 Mbps, four pairs w/3
2.Cat 4 Data grade up to 16 Mbps, four twisted
3.Cat 5 Data grade up to 100 Mbps, four twisted
- UTP is particularly susceptible to crosstalk,
which is when signals from one line get mixed up
with signals from another.
- easily tapped (because there is no shielding)
- 100 meters is shortest distance => attenuation
is the biggest problem here.
Shielded Twisted Pair (STP)
- Uses a woven copper braid jacket and a higher
quality protective jacket. Also uses foil wrap
between and around the wire pairs.
- Much less susceptible to interference and
supports higher transmission rates than UTP.
- Shielding makes it somewhat harder to install.
- same 100 meter limit as UTP.
- harder to tap
- used in AppleTalk and Token Ring networks
Fiber Optic Cable
- Consists of a small core of glass or plastic
surrounded by a cladding layer and jacket.
- Fibers are unidirectional (light only travels in
one direction) so two fibers are used, one for
sending and one for receiving. Kelvar fibres are
placed between the two fibres for strength.
- Good for very high speed, long distance data
- NOT subject to electrical interference.
- Cable can't be tapped and data stolen => high
- Most expensive and difficult to work with.
- Immune to tapping.
- can transmit at 100 Mbps and way up to 2 Gbps up
to 2000 meters without a repeater.
- Supports data, voice and video.
- needs specialized knowledge to install =>
expensive all round.
- Used where cable isn't possible - remote sites;
also when mobility is important.
- Use transceivers or access points to send and
receive signals between the wired and wireless
Techniques for transmitting data
- Infrared transmission consists of four
1. Line of sight
2. Scatter: good within 100 ft.
4. Broadband optical telepoint: used for multimedia
requirements; as good as cable.
- Laser requires direct line-of-sight.
- Narrow-band (single frequency) radio
- Cannot go through steel or load-bearing
- Requires a service handler.
- Limited to 4.8 Mbps
- Spread-Spectrum Radio
- Signals over a range of frequencies.
- Uses hop timing for a predetermined length
- Coded for data protection.
- Quite slow; Limited to 250 Kbps.
Point to Point Transmission
- Transfers data directly from PC to PC (NOT
through cable or other peripherals)
- Uses a point to point link for fast error-free
- Penetrates objects.
- Supports data rates from 1.2 to 38.4 Kbps up to
200 feet indoors or 1/3 of a mile with line of site
transmission. Also communicates with printers, bar
code readers, etc
Uses wireless public carriers to transmit and receive
- Packet-radio communication. Uplinked to
satellite, broadcast only to device which has
- Cellular networks. CDPD same as phone, subsecond
delays only, real time transmission, can tie into
- Satellite stations. Microwave, most common in
USA, 2 X directional antennas, building to building,
building to satellite
Baseband Transmission -- Digital
- Baseband transmission uses digital signaling
over a single frequency.
- Entire communication channel is used to transmit
a single signal.
- Flow is bi-directional. Some can transmit and
receive at the same time.
- Baseband systems use repeaters to strengthen
Broadband Transmission -- Analog
- Broadband uses analog signaling over a range of
- Signals are continuous and non-discrete.
- Flow is uni-directional and so two frequency
channels or two separate cables must be used. If
enough bandwidth is available, multiple analog
transmission systems such as cable TV AND network
transmissions can be on the same cable at the same
time. if this is the case, ALL devices must be tuned
to use only certain frequencies Uses amplifiers for
The OSI Model
- International Standards Organization (ISO)
specifications for network architecture.
- Called the Open Systems Interconnect or OSI
- Seven layered model, higher layers have more
- Each layer provides services for the next higher
- Each layer communicates logically with its
associated layer on the other computer.
- Packets are sent from one layer to another in
the order of the layers, from top to bottom on the
sending computer and then in reverse order on the
- Serves as a window for applications to access
- Handles general network access, flow control and
- Example Protocols are NCP, SMB, SMTP, FTP, SNMP,
- Determines the format used to exchange data
among the networked computers.
- Translates data from a format from the
Application layer into an intermediate format.
- Responsible for protocol conversion, data
translation, data encryption, data compression,
character conversion, and graphics expansion.
- Redirector operates at this level.
- Example protocols are NCP, AFP, TDI
- Allows two applications running on different
computers to establish use and end a connection
called a Session.
- Performs name recognition and security.
- Provides synchronization by placing checkpoints
in the data stream.
- Implements dialog control between communicating
- Example protocol is NetBIOS
- Responsible for packet creation.
- Provides an additional connection level beneath
the Session layer.
- Ensures that packets are delivered error free,
in sequence with no losses or duplications.
- Unpacks reassembles and sends receipt of
messages at the receiving end.
- Provides flow control, error handling, and
solves transmission problems.
- Example Protocols are NetBEUI, TCP, SPX, and
- Responsible for addressing messages and
translating logical addresses and names into
- Determines the route from the source to the
- Manages traffic such as packet switching,
routing and controlling the congestion of data.
- Example Protocols are IP, IPX, NWLink, NetBEUI
Data Link Layer
- Sends data frames from the Network layer to the
- Packages raw bits into frames for the Network
layer at the receiving end.
- Responsible for providing error free
transmission of frames through the Physical layer.
- Transmits the unstructured raw bit stream over a
- Relates the electrical, optical mechanical and
functional interfaces to the cable.
- Defines how the cable is attached to the network
- Defines data encoding and bit synchronization.
Ethernet Network Architecture
- Baseband signaling.
- Linear or star-bus topology.
- Usually transmits at 10 Mbps with 100 Mbps
- Uses CSMA/CD for traffic regulation.
- IEEE specification 802.3.
- Uses thicknet, thinnet or UTP cabling
- Media is passive => it draws power from the
10 Mbps Topologies
- (10 = 10 Mbps; Base= Baseband; T = Twisted Pair)
- 10 Mbps, baseband over UTP.
- Usually wired in a physical star with a hub or
multiport repeater. Internally it uses a bus
signaling system like other Ethernet configurations
- Maximum segment length 100 meters (328 feet).
- Minimum between computers 2.5 meters (8 feet).
- 1024 nodes maximum on the LAN
- Category 3, 4 or 5 UTP.
- RJ-45 connectors, 4 twisted pair.
- Coaxial or Fiber backbone for larger LAN's
- (10 = 10 Mbps; Base= Baseband; 2 = 2x 100
- 10 Mbps, baseband over thinnet.
- Uses bus topology.
- Maximum segment length 185 meters (607 feet).
- Minimum between computers 0.5 meters (20
- Maximum of 30 computers per segment.
- (10 = 10 Mbps; Base= Baseband; 5 = 5 x 100
- 10 Mbps, baseband over thicknet.
- Also called Standard Ethernet
- Designed to support a backbone for a large
department or building. Transceivers attach to the
thicknet cable and the cable AUI connector plugs
into a repeater . The branching segments of thinnet
plug into the repeater and connect to the computers
on the network.
- Uses bus topology.
- Maximum segment length 500 meters.
- Minimum between transceivers 2.5 meters (8 feet)
- 100 computers per segment, 300 per network.
- Transceiver is attached to main segment with a
- DIX or AUI connector is used to attach the
transceiver to the network card. Maximum computer to
transceiver distance is 50 meters. This distance is
not included in the 5-4-3 calculation.
- (10 = 10 Mbps; Base= Baseband; FL =fibre optic)
- Allows long cable runs between repeaters, like
- Maximum segment length 2000 meters.
- 10BaseFL - Used for linking computers in
a LAN environment.
- 10BaseFP - Used for linking computers
with passive hubs from maximum cable distance up to
- 10BaseFB - Used as a backbone between
- Baseband signal over a fiber-optic cable.
- Need concentrator (fiber-optic hub) ® Star wired
(star topology) . Either active or passive
- Long distance.
- Very expensive. Difficult to install.
100 Mbps Topologies
100VG-AnyLAN (IEEE 802.12)
- 100 Mbps data rate.
- Star topology over Category 3, 4 and 5 UTP.
- Uses demand priority access.
- Combines element of traditional Ethernet and
Token Ring and supports Ethernet and token ring
- Faster than Ethernet
- Demand priority access method => two priority
levels, low and high
- Intelligent hubs can filter individually
addressed frames for enhanced privacy.
- Uses RJ-45.
- Uses star topology and defines how child hub can
be connected to a parent hub to extend the network.
100BaseT? (Fast Ethernet)
- Uses CSMA/CD on a star-wired bus.
- There are 3 specifications:
- 100BaseT4: Uses pair category 3, 4 or 5 UTP.
- 100BaseTX: Uses 2-pair category 5 UTP or
- 100BaseFX: Uses 2-strand fiber-optic
Token Ring Network Architecture
- IEEE 802.5 specification.
- Star wired ring topology (logical ring)
- Uses token passing access method.
- Can have higher transmission speeds than
- It has larger frames than Ethernet => more can
get transferred over the wire in any given time.
- Uses IBM STP Types 1, 2 and 3 cabling. (Can be
- Transmits at 4 and 16 Mbps. (16 Mbps cards will
slow down to 4 Mbps if put on that kind of network,
but the 4 Mbps cards can't speed up.
- Baseband transmission
- Data travels in one direction only
- Each computer acts as a unidirectional repeater
- Deterministic method of cable access. Computers
cannot use the cable unless they have the token.
Therefore, computers can't force their way onto the
network like CSMA/CD (Ethernet)
- First computer online is assigned to monitor
Token Ring Components
- Multistation Access Units (MSAU's)
- Smart Multistation Access Units (SMAU's)
- Computers attach directly to the MSAU in a
physical star to form a logical ring.
- Each MSAU has 10 connection ports ==> can
support 8 clients with 2 ports for ring in and ring
- Each ring can have as many as 33 MSAU's
- Up to 12 MSAU's can connect to each other
- The MSAU can sense if a computer is down and
then disconnect it from the ring => built-in fault
- Most token ring systems use IBM type 3 cabling.
- Token ring networks are well suited to fiber
optic cable: data travels in only one direction in
- local talk
- CSMA/CA access method
- 3 things happen when devices attached
1. device assigns itself an address randomly
2. device broadcasts the address to see if it's
3. if not, the device will use it the next time
it's online again
- bus or tree
- max. 32 devices
- Apple share
- file server on an AppleTalk network
- divided into zones
- allows protocols to run on ethernet coaxial
- TokenTalk -802.5 which allows Macintosh to
connect to token ring network
Protocols are rules and procedures for communication.
Protocol Stacks (or Suites)
A combination of protocols, each layer performing a
function of the communication process to ensure that
data is prepared, transferred, received and acted upon.
- IBM SNA (Systems Network Architecture)
- Digital DECnet
- Novell NetWare
- Apple AppleTalk
Work at the upper layer of the OSI model and provide
application to application interaction and data
- APPC-IBM's peer to peer SNA protocol used on
- FTAM: an OSI file access protocol.
- X.400: international e-mail transmissions.
- X.500: file and directory services across
- SMTP: Internet e-mail.
- FTP: Internet file transfer
- SNMP: Internet network management protocol.
- Telnet: Internet protocol for logging on to
- Microsoft SMB: client shells and redirectors.
- NCP: Novell client shells or redirectors.
- AppleTalk and AppleShare: Apple's protocol
- AFP: Apple's protocol for remote file access.
- DAP (data access protocol): DECnet file access
These protocols provide communication sessions between
computers and ensure data is moved reliably between
- TCP (transmission control protocol): internet
protocol for guaranteed delivery of sequenced data.
- SPX (sequenced packet exchange): Novell protocol
- NWLink: Microsoft implementation of IPX/SPX.
- NetBEUI: establishes communications sessions
between computers and provides the underlying data
- ATP, NBP: Apple's communication session and
These provide link services They also handle addressing
and routing, error checking and retransmission requests
and define rules for Ethernet or Token Ring.
- IP (Internet Protocol): packet forwarding and
- IPX: (Internetwork Packet Exchange): Novell's
protocol for packet forwarding and routing.
- NWLink: Microsoft implementation of IPX/SPX.
- NetBEUI: Transport for NetBIOS sessions and
- DDP (datagram delivery protocol): An AppleTalk
data transport protocol.
The IEEE protocols at the Physical Layer
802.3 (CSMA /CD - Ethernet)
- Logical bus network
- Can transmit at 10 Mbps
- Data is transmitted on the wire to every
computer but only those meant to receive respond
- CSMA /CD protocol listens and allows
transmission when the wire is clear
802.4 (Token Passing)
- Bus layout that used token passing
- Every computer receives all of the data but only
the addressed computers respond
- Token determines which computer can send
802.5 (Token Ring)
- Logical ring network; physical set up as star
- Transmits at 4 Mbps or 16 Mbps
- Token determines which computer can send
- Provides communications in a heterogeneous
- Routable, defacto standard for internetworking.
- SMTP, FTP, SNMP are protocols written for TCP/IP
- Disadvantages are size and speed.
- NetBIOS extended user interface.
- Originally, NetBIOS and NetBEUI were tightly
tied together but, NetBIOS has been separated out to
be used with other routable protocols. NetBIOS acts
as a tool to allow applications to interface with
the network; by establishing a session with another
program over the network
- NetBIOS operates at the Session layer.
- Small, fast and efficient.
- Compatible with most Microsoft networks.
- Not routable and compatible only with Microsoft
- Protocols incorporated in a packet switching
network of switching services.
- Originally established to connect remote
terminals to mainframe hosts.
- Xerox Network System.
- Developed for Ethernet LANs but has been
replaced by TCP/IP.
- Large, slow and produces a lot of broadcasts.
IPX/SPX and NWLink
- Used for Novell networks.
- Small and fast.
- Advanced Program to Program Communication
- Developed by IBM to support SNA.
- Designed to enable application programs running
on different computers to communicate and exchange
Apple's proprietary protocol stack for Macintosh
OSI Protocol Suite
Each protocol maps directly to a single layer of the OSI
- Digital Equipment's proprietary protocol stack
- Defines communications over Ethernet, FDDI MAN's
- DECnet can also use TCP/IP and OSI protocols as
well as its own protocols
Putting data on the Cable
This stands for "carrier-sense multiple access with
collision detection" and is the method used on ethernet
networks whereby all computers on the network check the
cable for traffic before attempting to transmit a
packet. If more than 1 transmits at the same time then
there will be a collision and both computers will wait a
random amount of time and retransmit.
Stands for "carrier-sense multiple access with collision
avoidance". This access method prevents collisions by
having computers broadcast an intent to send a packet.
This is the access method used by Localtalk and is
sometimes described as "chatty". This broadcasting of
intent to send can cause excess network traffic and slow
Token passing is the access method used by token ring
networks. With this method, a packet called a token is
passed around the network. A computer that wishes to
transmit must wait until it can take control of the
token, allowing only one computer to transmit at a time.
This is sort of like the "conch" in Lord of the Flies.
Piggy had all of this crap that he wanted to whine about
all of the time, but could only do so if he possessed
This access method is used with 100VG-AnyLAN networks.
The repeaters, bridges, routers or hubs search the
network for requests that are waiting to be sent. If 2
or more requests are received by the network hardware at
once, the data with the highest priority is sent.
Priority for different data types can be controlled by
the administrator. A real advantage is that computers
can receive and transmit at the same time with this
Network Adapter Cards
The role of the network Adapter card it to:
- Prepare data from the computer for the network
- Send the data to another computer
- Control the flow of data between the computer
and the cabling system
NIC's contain hardware and firmware (software
routines in ROM) programming that implements the Logical
Link Control and Media Access Control functions of the
Data Link layer of the OSI
- EXTEND the network segment by REGENERATING the
signal from one segment to the next
- Repeaters regenerate BASEBAND, digital signals
- Don't translate or filter anything
- Is the least expensive alternative
- work at the Physical layer of OSI
- Both segments being connected must use the same
access method e.g. an 802.3 CSMA/CD (Ethernet) LAN
segment can't be joined to a 802.5 (Token Ring) LAN
segment. Another way of saying this is the Logical
Link Protocols must be the same in order to send a
- BUT repeaters CAN move packets from one physical
medium to another: for example can take an Ethernet
packet from a thinnet coax and pass it on to a
fiber-optic segment. Same access method is being
used on both segments, just a different medium to
deliver the signal
- They send every bit of data on => NO FILTERING,
so they can pass a broadcast storm along from on
segment to the next and back. So you want to use a
repeater when there isn't much traffic on either
segment you are connecting.
- There are limits on the number of repeaters
which can be used. The repeater counts as a single
node in the maximum node count associated with the
Ethernet standard [30 for thin coax].
- Repeaters also allow isolation of segments in
the event of failures or fault conditions.
Disconnecting one side of a repeater effectively
isolates the associated segments from the network.
- Using repeaters simply allows you to extend your
network distance limitations. It does not give you
any more bandwidth or allow you to transmit data
- Why only so many repeaters are allowed on a
single network: "propagation delay". In cases where
there are multiple repeaters on the same network,
the brief time each repeater takes to clean up and
amplify the signal, multiplied by the number of
repeaters can cause a noticeable delay in network
- It should be noted that in the above diagram,
the network number assigned to the main network
segment and the network number assigned to the other
side of the repeater are the same.
- In addition, the traffic generated on one
segment is propagated onto the other segment. This
causes a rise in the total amount of traffic, so if
the network segments are already heavily loaded,
it's not a good idea to use a repeater.
- A repeater works at the Physical Layer by simply
repeating all data from one segment to another.
- Have all the abilities of a repeater
- Take an overloaded network and split it into two
networks, therefore they can divide the network to
isolate traffic or problems and reduce the traffic
on both segments
- Expand the distance of a segment
- Link UNLIKE PHYSICAL MEDIA such as twisted-pair
(10Base T) and coaxial Ethernet (10Base2)
- They can link UNLIKE ACCESS CONTROL METHODS, on
different segments such as Ethernet and Token Ring
and forward packets between them. Exam Cram says
this is a Translation Bridge that can do this - not
all bridges - but my observation is questions don't
necessarily mention the distinction.
- Bridges work at the Data Link Layer of the OSI
model => they don't distinguish one protocol from
the next and simply pass protocols along the
network. (use a bridge to pass NetBEUI, a
non-routable protocol, along the network)
- Bridges actually work at the MEDIA ACCESS
CONTROL (MAC) sublayer. In fact they are sometimes
called Media Access Control layer bridges. Here's
how they deal with traffic:
- They listen to all traffic. Each time the bridge
is presented with a frame, the source address is
stored. The bridge builds up a table which
identifies the segment to which the device is
located on. This internal table is then used to
determine which segment incoming frames should be
forwarded to. The size of this table is important,
especially if the network has a large number of
- They check the source and destination address of
- They build a routing table based on the SOURCE
ADDRESSES. Soon they know which computers are on
- Bridges are intelligent enough to do some
- If the destination address is on the routing
table and is on the SAME SEGMENT, the packet isn't
forwarded. Therefore, the bridge can SEGMENT network
- If the destination address is the routing table,
and on a remote segment, the bridge forwards the
packet to the correct segment
- If the destination address ISN'T on the routing
table, the bridge forwards the packet to ALL
- BRIDGES SIMPLY PASS ON BROADCAST MESSAGES, SO
they too contribute to broadcast storms and don't
help to reduce broadcast traffic
- Two segments are joined by a bridge on each
side, each connected to a synchronous modem and a
- There is a possibility that data might get into
a continuous loop between LANs
- The SPANNING TREE ALGORITHM (STA)
- Senses the existence of more than one route
- Determines which is the most efficient and
- Configures the bridge to use that route
- This route can be altered if it becomes
- Transparent bridges (also known as
spanning tree, IEEE 802.1 D) make all routing
decisions. The bridge is said to be transparent
(invisible) to the workstations. The bridge will
automatically initialize itself and configure
its own routing information after it has been
- Determine the best path for sending data and
filtering broadcast traffic to the local segment.
They DON'T pass on broadcast traffic
- Work at the Network layer of OSI => they can
switch and route packets across network segments
- They provide these functions of a bridge:
filtering and isolating traffic and connecting
- Routing table contains
1. all known network addresses
2. how to connect to other networks
3. possible paths between those routers
4. costs of sending data over those paths
5. not only network addresses but also media access
control sublayer addresses for each node
- Routers require specific addresses: they only
understand network numbers which allow them to talk
to other routers and local adapter card addresses
- Only pass Packets to the network segment they
are destined for.
- Routers don't talk to remote computers, only to
- They can segment large networks into smaller
- They act as a safety barrier (firewall) between
- They prohibit broadcast storms, because
broadcasts and bad data aren't forwarded
- Can join dissimilar access methods: a router can
route a packet from a TCP/IP Ethernet network to a
TCP/IP Token Ring network
- Routers don't look at the destination computer
address. They only look at the NETWORK address and
they only pass on the data if the network address is
known => less traffic
- Routable protocols have Network layer
addressing embedded For Example:DECnet, IP, IPX,
OSI, XNS, DDP (Apple)
- Non-routable protocols don't have network
layer addressing .For Example LAT, NetBEUI, DLC
- Routers can choose the best path for the data to
- Routers can accommodate multiple active paths
between LAN segments. To determine the best path, it
takes these things into account:
- If one path is down, the data can be
forwarded over on alternative route
- Routers can listen and determine which parts
of the network are busiest.
- It decides the path the data packet will
follow by determining the number of hops between
- OSPF (Open Shortest Path First)
- It is a link-state routing algorithm
- Routes are calculated based on
- # of hops
- line speed
- TCP/IP supports OSPF
- RIP (Routing Information Protocol)
- RIP is the protocol used to determine the #
of hops to a distant segment.
- Uses distance-vector algorithm to determine
- TCP/IP & IPX support RIP
- NLSP (NetWare Link Services Protocol) is
a link-state algorithm for use with IPX
- There are 2 types of routers
- Static - manually setup and config
the routing table and to specify each route
- Dynamic automatic discovery of
routers and use information from other routers
There are many types of hubs:
- Passive hubs are don't require power and
are simple splitters or combiners that group
workstations into a single segment
- Active hubs require power and include a
repeater function and are thus capable of supporting
many more connections.
- Intelligent hubs provide packet switching
and traffic routing
- The TRANSLATOR -- allows communications between
dissimilar systems or environments
- A gateway is usually a computer running gateway
software connecting two different segments. For
example an Intel-based PC on one segment can both
communicate and share resources with a Macintosh
computer or an SNA mainframe. Use gateways when
different environments need to communicate. One
common use for gateways is to translate between
personal computers and mainframes
- GSNW is a gateway to allow Microsoft clients
using SMB to connect to a NetWare server using NCP.
- Gateways work at the Application --> Transport
- They make communication possible between
different architectures and environments
- They perform protocol AND data conversion /
- They takes the data from one environment, strip
it, and re-package it in the protocol stack from the
- They repackage and convert data going from one
environment to another so that each environment can
understand the other environment's data
- Gateway links two systems don't use the same
protocols ,data formatting structure,languages and
- They are task specific in that they are
dedicated to a specific type of conversion: e.g.
"Windows NT Server -> SNA Server Gateway"
- Usually one computer is designated as the
gateway computer. This adds a lot of traffic to that
An IP (Internet Protocol) address is a unique
identifier for a node or host connection on an IP
network. An IP address is a 32 bit binary number usually
represented as 4 decimal values, each representing 8
bits, in the range 0 to 255 (known as octets) separated
by decimal points. This is known as "dotted decimal"
It is sometimes useful to view the values in their
140 .179 .220 .200
Every IP address consists of two parts, one identifying
the network and one identifying the node. The Class of
the address and the subnet mask determine which part
belongs to the network address and which part belongs to
the node address.
There are 5 different address classes. You can determine
which class any IP address is in by examining the first
4 bits of the IP address.
Class A addresses begin with 0xxx, or 1 to 126 decimal.
Class B addresses begin with 10xx, or 128 to 191
Class C addresses begin with 110x, or 192 to 223
Class D addresses begin with 1110, or 224 to 239
Class E addresses begin with 1111, or 240 to 254
Addresses beginning with 01111111, or 127 decimal, are
reserved for loopback and for internal testing on a
local machine. [You can test this: you should always be
able to ping 127.0.0.1, which points to yourself] Class
D addresses are reserved for multicasting. Class E
addresses are reserved for future use. They should not
be used for host addresses.
Now we can see how the Class determines, by default,
which part of the IP address belongs to the network (N)
and which part belongs to the node (n).
Class A -- NNNNNNNN.nnnnnnnn.nnnnnnn.nnnnnnn
Class B -- NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn
Class C -- NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn
In the example, 184.108.40.206 is a Class B address so
by default the Network part of the address (also known
as the Network Address) is defined by the first two
octets (140.179.x.x) and the node part is defined by the
last 2 octets (x.x.220.200).
In order to specify the network address for a given IP
address, the node section is set to all "0"s. In our
example, 220.127.116.11 specifies the network address for
18.104.22.168. When the node section is set to all
"1"s, it specifies a broadcast that is sent to all hosts
on the network. 22.214.171.124 specifies the example
broadcast address. Note that this is true regardless of
the length of the node section.
There are three IP network addresses reserved for
private networks. The addresses are 10.0.0.0/8,
172.16.0.0/12, and 192.168.0.0/16. They can be used by
anyone setting up internal IP networks, such as a lab or
home LAN behind a NAT or proxy server or a router. It is
always safe to use these because routers on the Internet
will never forward packets coming from these addresses
Subnetting an IP Network can be done for a variety of
reasons, including organization, use of different
physical media (such as Ethernet, FDDI, WAN, etc.),
preservation of address space, and security. The most
common reason is to control network traffic. In an
Ethernet network, all nodes on a segment see all the
packets transmitted by all the other nodes on that
segment. Performance can be adversely affected under
heavy traffic loads, due to collisions and the resulting
retransmissions. A router is used to connect IP networks
to minimize the amount of traffic each segment must
Applying a subnet mask to an IP address allows you to
identify the network and node parts of the address. The
network bits are represented by the 1s in the mask, and
the node bits are represented by the 0s. Performing a
bitwise logical AND operation between the IP address and
the subnet mask results in the Network Address or
Number. For example, using our test IP address and the
default Class B subnet mask, we get:
Class B IP Address
Default Class B Subnet Mask
Default subnet masks
Class A - 255.0.0.0 -
Class B - 255.255.0.0 -
Class C - 255.255.255.0 -
CIDR -- Classless InterDomain Routing.
CIDR was invented several years ago to keep the internet
from running out of IP addresses. The "classful" system
of allocating IP addresses can be very wasteful; anyone
who could reasonably show a need for more that 254 host
addresses was given a Class B address block of 65533
host addresses. Even more wasteful were companies and
organizations that were allocated Class A address
blocks, which contain over 16 Million host addresses!
Only a tiny percentage of the allocated Class A and
Class B address space has ever been actually assigned to
a host computer on the Internet. People realized that
addresses could be conserved if the class system was
eliminated. By accurately allocating only the amount of
address space that was actually needed, the address
space crisis could be avoided for many years. This was
first proposed in 1992 as a scheme called Supernetting.
The use of a CIDR notated address is the same as for a
Classful address. Classful addresses can easily be
written in CIDR notation (Class A = /8, Class B = /16,
and Class C = /24) It is currently almost impossible for
an individual or company to be allocated their own IP
address blocks. You will simply be told to get them from
your ISP. The reason for this is the ever-growing size
of the internet routing table. Just 5 years ago, there
were less than 5000 network routes in the entire
Internet. Today, there are over 90,000. Using CIDR, the
biggest ISPs are allocated large chunks of address space
(usually with a subnet mask of /19 or even smaller); the
ISP's customers (often other, smaller ISPs) are then
allocated networks from the big ISP's pool. That way,
all the big ISP's customers (and their customers, and so
on) are accessible via 1 network route on the Internet.
It is expected that CIDR will keep the Internet happily
in IP addresses for the next few years at least. After
that, IPv6, with 128 bit addresses, will be needed.
Under IPv6, even sloppy address allocation would
comfortably allow a billion unique IP addresses for
every person on earth.
Name resolution for TCP/IP
Name resolution is a process that provides users with
easy-to-remember server names, instead of requiring them
to use the numerical IP addresses by which servers
identify themselves on the TCP/IP network. The
name-resolution services are the DNS and WINS.
Domain Name System(DNS)
DNS is a hierarchical naming system used for locating
computers on the Internet and private TCP/IP networks.It
is used to map Internet domain and computer names into
IP addresses and vice versa. DNS works at the
application layer and uses TCP and UDP for transport.
TCP is only used if returned data is truncated. DNS was
originally based on HOSTS files that were maintained by
a centralized Network Information Center. Today it is
based on a hierarchy of servers with a distributed
hierarchical database throughout the network or
Internet. One or more DNS servers are needed in most
installations. DNS is required for Internet e-mail; Web
browsing, and Active Directory. DNS is also required in
domains with clients running Windows 2000. DNS is
installed automatically when you create a domain
controller (or promote a server to become a domain
controller), unless the Windows 2000 software detects
that a DNS server already exists for that domain.
(Alternatively, you can explicitly select DNS as a
component to install during or after Setup.)
DNS is a hierarchical naming structure with the
Notice that the highest level of the domain is listed
last. An example of a domain name that you may be
familiar with is: Microsoft.com.
- Root designated by a dot (.).
- First level - This indicates country or type of
organization such as "org", "com", and "net".
- Second level - Indicates the organization name
and can be purchased for a yearly fee.
On the client side, a DNS resolver is used to send
queries to DNS servers. The resolver is normally part of
a library routine or it is built into the application.
DNS uses zone files to keep name and IP address database
information for the internet domain or hierarchial set
of domains. Zones are a storage of information in a file
for a DNS domain or DNS subdomains (DNS domains are not
the same as Windows domains). DNS does not yet support
dynamic configuration but has been modified for Windows
systems to do so. Different aliases may be created by
the administrator for the same host. Three types of name
servers as defined by how it relates to the zone
- Primary - Locally stored files exist on
the name server database. The master zone file copy
is stored here.
- Secondary - Gets data called a zone
transfer from another server that is the zone
- Caching Only - Caches name server
information and does not contain its own files.
A primary and secondary name server should be used on
a network. When a zone is defined, some server must be
configured to be a master name server for the zone.
There can be different master name servers for different
zones. The master server provides copies of the zone
information to the secondary DNS server. Name servers
can be configured to get information from other name
servers when the information is not found in the local
database. These types are forwarders and slaves. Name
servers as categorized by function:
- Master - The zone authority that contains
the master zone files.
- Forwarders - A name server that passes
name resolution requests to other name servers. This
configuration is done on a per server basis.
- Slaves - Slave name servers are
configured to use forwarders.
Query types are:
- Inverse - Getting the name from the IP
address. These are used by servers as a security
- Iterative - Server gives its best answer.
This type of inquiry is sent from one server to
- Recursive - Cannot refer the query to
another name server.
The DNS zone file serial number is used to track DNS
changes. The notify function is used to initiate zone
transfers. Zone transfer types are:
- Full - AXFR Query - Secondary server
refresh interval expires and it sends an AXFR query.
- Incremental - IXFR query - Only new or
updated entries are copied.
Possible zones include:
- Forward lookup zone - Name to IP address
- Reverse lookup zone - IP address to name
- Standard primary zone (primary zone) - A
master copy of a forward or reverse lookup zone.
- Standard secondary zone (secondary zone)
DNS Record types
- A - Address record allowing a computer
name to be translated into an IP address. Each
computer must have this record for its IP address to
be located. These names are not assigned for clients
that have dynamically assigned IP addresses, but are
a must for locating servers with static IP
- CNAME - Canonical name allowing
additional names or aliases to be used to locate a
- MX - Mail Exchange server record. There
may be several.
- NS - Name server record. There may be
- PTR - Pointer resource record.
- SOA - Start of Authority record defines
the authoritative server and parameters for the DNS
zone. These include timeout values, name of
- SRV - Service locator resource record to
map a service to servers providing the service.
Windows 2000 clients will use this record to find a
Dynamic host configuration protocol is used to
automatically assign TCP/IP addresses to clients along
with the correct subnet mask, default gateway, and DNS
- Scope - A range of IP addresses that the DHCP
server can assign to clients that are on one subnet.
- Superscope - A range of IP addresses that span
several subnets. The DHCP server can assign these
addresses to clients that are on several subnets.
- Multicast scope - A range of class D addresses
from 126.96.36.199 to 188.8.131.52 that can be
assigned to computers when they ask for them. A
multicast group is assigned to one IP address.
Multicasting can be used to send messages to a group
of computers at the same time with only one copy of
the message. The Multicast Address Dynamic Client
Allocation Protocol (MADCAP) is used to request a
multicast address from a DHCP server.
There are global and scope options.Global
options apply to all client computers.Scope
options apply to specific subnets or range of IP
Understanding Windows Internet Naming System(WINS)
Provides name resolution for clients running Windows NT
and earlier versions of Microsoft operating systems.
With name resolution, users can access servers by name,
instead of having to use IP addresses that are difficult
to recognize and remember. The purpose of WINS is to
allow a NetBIOS name to be mapped to an IP address.
Therefore computers using WINS must be using NBT
(NetBIOS over TCP/IP). WINS was originally put in place
to compensate for a shortcoming of NetBEUI which is the
fact that it is not routable. Therefore on large
Networks IP is used to transport NetBIOS and rather than
using broadcasts, information is sent to the WINS
server. WINS maps Windows computer names to IP addresses
but does not do name lookups based on IP addresses. The
use of Windows Explorer or NET commands invokes the
NetBIOS interface. NetBIOS names, if repeated on another
domain that is on the network, may cause a problem since
there is no way to distinguish NetBIOS names between two
domains. Each computer, when booted, sends a name
registration broadcast. If there is no response, the
computer will use the name it registered. A NetBIOS
broadcast releases the computer name when the computer
is shutdown gracefully. WINS reduces this broadcast
traffic when using NBT. The registration and release is
sent to the WINS server rather than being broadcast. The
clients have the IP address of the WINS server and they
are configured to use WINS before using NetBIOS
broadcasts. A backup WINS server may be available on the
network for fault tolerance.
Five NBT Name Resolution Methods
- B-node - broadcast - Uses UDP broadcast
data grams. Default node type.
- P-node - Peer to peer - Uses a Net BIOS
name server such as WINS. If a WINS server is not
available, broadcasts are not used as a backup. The
WINS IP address must be specified at each client.
- M-node - Mixed - Tries B-node, then
- H-node - Hybrid - Tries P-node, then
B-node resolution. After this attempt for Windows
2000, LMHOSTS and HOSTS files are used, and then the
DNS server is used.
- Microsoft enhanced B-node - Checks address
cache, which is loaded from the LMHOSTS file when
the system boots. After checking address cache, a
broadcast is sent, then the LMHOSTS file is checked
if broadcasting did not resolve the query.
On the WINS server, there is a NetBIOS name for each
service a NetBIOS computer offers. This uses the 16th
hidden character of the NetBIOS names. Up to 25 records
of groups, domain browsers, and multihomed computers may
WINS Proxy Agent
A WINS proxy agent can be configured to act as a relay
for non-WINS clients. The WINS proxy agent can intercept
client broadcast requests, forward them to a WINS server
and return the response. It may also reply with the
response without contacting the WINS server if the
required information is in its cache. One WINS proxy is
used on each subnet that has non-WINS clients. This
means that machines that are not using WINS (Even
Windows machines such as those without TCP/IP) can use a
proxy agent to let them find resources on other subnets.
There should be a maximum of two proxy agents per
subnet. The agent must be a Windows based client, not a
server. When NetBIOSs names are registered, both the
proxy agent and the WINS server checks the name.
When two WINS servers are configured to communicate with
each other replication occurs any time the data base on
one of them changes. Servers are configured as a push or
pull partner. A server can be both a push and pull
partner. Push partners send update notices when a
database change is made. A pull partner asks push
partners for database entries more recent than their
current listings. Only changes are replicated. Pull
servers are used across slow links since pull requests
can be set for specific times.
- A pull server will pull updates when it is
started, then at chosen times thereafter.
- A push partner will send updates when a change
threshold is reached. A threshold and update
interval may be set.
Examining your network with commands
PING is used to check for a response from another
computer on the network. It can tell you a great deal of
information about the status of the network and the
computers you are communicating with. Ping returns
different responses depending on the computer in
question. The responses are similar depending on the
options used. Ping uses IP to request a response from
the host. It does not use TCP .It takes its name from a
submarine sonar search - you send a short sound burst
and listen for an echo - a ping - coming back. In an IP
network, `ping' sends a short data burst - a single
packet - and listens for a single packet in reply. Since
this tests the most basic function of an IP network
(delivery of single packet), it's easy to see how you
can learn a lot from some `pings'. To stop ping, type
control-c. This terminates the program and prints out a
nice summary of the number of packets transmitted, the
number received, and the percentage of packets lost,
plus the minimum, average, and maximum round-trip times
of the packets.
NSLOOKUP is an application that facilitates looking up
hostnames on the network. It can reveal the IP address
of a host or, using the IP address, return the host
name. It is very important when troubleshooting problems
on a network that you can verify the components of the
networking process. Nslookup allows this by revealing
details within the infrastructure.
NETSTAT is used to look up the various active
connections within a computer. It is helpful to
understand what computers or networks you are connected
to. This allows you to further investigate problems. One
host may be responding well but another may be less
This is a Microsoft windows NT, 2000 command. It is very
useful in determining what could be wrong with a
network. This command when used with the /all switch,
reveal enormous amounts of troubleshooting information
within the system.
Traceroute on Unix and Linux (or tracert in the
Microsoft world) attempts to trace the current network
path to a destination.
Network Operating Systems
A networking operating system designed using a Directory
to manage certain resources. NT's primary file system is
NTFS. Provides an inherently GUI console at the server.
Clients - Windows NT Workstation best serves Windows NT
Server because of the common NTFS file system and they
are optimized to work best with each other. However,
Windows95/98, Windows for Workgroups, DOS, UNIX,
Macintosh, and even NetWare clients can be connected to
a Windows NT environment.
A product in Microsoft's Windows line of operating
systems. There are four versions of Windows 2000:
Professional -- an operating system for business desktop
and laptop systems. It is used to run software
applications, connect to Internet and intranet sites,
and access files, printers, and network resources.
Server - both a Web server and an office server. Windows
2000 Server lets users build Web applications and
connect to the Internet. Advanced Server - an operating
for line-of-business applications and e-commerce. It
contains all the functionality of the standard version
of Windows 2000 Server, plus additional features for
applications that require higher levels of scalability
and availability. Data Center Server - developed to work
in high-traffic computer networks, it is designed for
enterprises that need reliable high-end drivers and
software. It supports up to 32-way SMP and up to 64 GB
of physical memory.
Windows XP is the newest operating system from
Microsoft. The release of XP means that all the desktop
versions are now built on the Windows NT/2000 code base
(rather than the shakier foundation of Windows
95/98/ME). This has vastly simplified the range, as well
as bringing the stability of this code base to home
users for the first time. For anyone who runs Windows
3.1, 95, 98 or ME, it is strongly recommended as the
benefits of XP will be huge. XP also has "remote"
technology, taken from Microsoft's Terminal Server
technology, with variations of it being included in both
Home and Professional editions. The user can allow a
remote helper to view their desktop, or optionally gain
control of the keyboard and mouse, in order to
troubleshoot a problem. Windows XP comes in two version,
Home and Professional. The company has focused on
mobility for both editions, including plug and play
features for connecting to wireless networks. The
operating system also utilizes the 802.11x wireless
A networking operating system designed using a bindery
or Directory Service to manage most resources. NetWare’s
primary file system is a combination of FAT (File
Allocation Table) and DET (Directory Entry Table).
Provides an inherently text based and command prompt
console at the server.Novell NetWare works well with
most popular clients such as DOS, Windows 3.11, Windows
9x, Windows NT Workstation.
UNIX is a command line operating system written in the C
programming language. GUI interface can be achieved by
installing special software such as X-Windows. Used
mainly in a multi-user environment on minicomputers.
Several different version available and allows a great
deal of flexibility when performing network operations.
Many UNIX protocols are the standard for today’s
A freely-distributable open source implementation of
UNIX that runs on a number of hardware platforms,
including Intel and Motorola microprocessors. It was
developed mainly by Linus Torvalds. Because it's free,
and because it runs on many platforms, including PCs,
Macintoshes and Amigas, Linux has become extremely
popular over the last couple years. Linux is an
extremely powerful Unix operating system that is
completely free. It has all the features of commercial
operating systems including true multitasking, virtual
memory, shared libraries, proper memory management and
TCP/IP networking. It runs on many different processors
including Intel x86, Motorola 68k series (Amiga and
Atari), DEC Alpha, Sun Sparc, Mips and Motorola PowerPC.
Solaris is a multiuser,multitasking operating systems
developed and sold by Sun Microsystems and it is one
implementation of the UNIX operating system that draws
on both the SystemV(AT&T) and Berkeley(BSD) systems. Its
an extremely powerful enterprise wide Network operating
system having inherent support of mobile
computing,clustering technology,,Security innovations
such as Kerberos V5,IP Sec as well as inclusion of IPv6.
Maintaining Your Network
In order to secure a system against loss of valuable
data, establish some sort of fault tolerance program.
This program will allow recovery of data should there be
a disk failure. RAID (Redundant Array of Inexpensive
Disks) is a method of disk configuration that will
assist in this goal.
Level 0-Disk Striping
Divides data into 64k blocks and spreads it equally
among all disks in the array. It 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
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 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
Types of Backups
- Normal - Saves files and folders and
shows they were backed up by clearing the archive
- Copy - Saves files and folders without
clearing the archive bit.
- Incremental - Saves files and folders
that have been modified since the last backup. The
archive bit is cleared.
- Differential - Saves files and folders
that have been modified since the last backup. The
archive bit is not cleared.
- Daily - Saves files and folders that have
been changed that day. The archive bit is not
- Room conditions - It's important to setup
the room with normal humidity to prevent
electrostatic discharge (ESD). Air conditioning
should be used to prevent the CPU from overheating.
Be sure to put the equipment in a secured room to
prevent someone from tampering with unsupervised
equipment during off hours.
- Building contents and personal effects -
Consider the effects of heat on electrical signals,
electromagnetic interference (EMI) from power lines
or unshielded power cables as well as TV and radio
interference. A common source of EMI is fluorescent
lights, elevator motors, large generators, and
- Computer equipment- Computer equipment
can affect the unshielded data cables with
electromagnetic interference (EMI), such as monitor
radiation or CPU power supplies. If the computer
equipment is faulty then the network components may
appear to have problems.
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