What is a
Computer Network?
So, what is a computer network exactly? A computer network
is a group of computers, two or more, connected to each other through a wire or
a cable or even wireless. You can share files with other computers this way
easily. If the network is large enough and lets you access a large number of
computers, it becomes even more useful. You can share a modem, printers,
storage space and DVD drives with the other computers on the network. You can
video conference with the other people using the network or you can work
together on a complex task with your connected systems. Learn more about how
computer networks communicate using the TCP/IP protocols with this course.
Different
Types of Networks
Networks are classified on basis of scale. The area a
network covers determines the type of network it is. Originally, there were
only two types of networks: LAN and WAN. But over the years, other types of
networks have evolved, like MAN, SAN, PAN, CAN and DAN. Let’s take a look at
the more popular ones:
LAN: LAN is the acronym for Local Access Network. A LAN
network is a short-distance network. It connects computers that are close
together, usually within a room or a building. Very rarely, a LAN network will
span a couple of buildings. An example of a LAN network is the network in a
school or an office building. A LAN network doesn’t need a router to operate.
WAN: WAN stands for Wide Area Network. WANs cover a huge
geographical area. A WAN is a collection of LAN networks. LANs connect to other
LANs with the help of a router. The router has a LAN address and a WAN address,
which lets it send data to the desired location. The biggest WAN in the world
is, of course, the Internet. WANs are different from LANs in that they’re not
owned by a single person/organization. They also use different technology that
enables them to communicate over long distances, like Frame Relay and ATM.
VPN: VPN stands for Virtual Private Networks. VPNs are very
important today. They let you connect to your network from a remote location
through the Internet. This saves you time and money- you don’t need to set up a
physical connection with your network. The Internet acts as a medium between
you and your network. For example, you can access your computer at work through
your computer at home.
MAN: MAN stands for Metropolitan Area Network. The network
in a metro area is a MAN. They are usually more limited in scope than WANs, but
essentially work the same way.
CAN: CAN stands for Campus Area Network. The network that
spans a University or College campus is a CAN. CANs are like WANs or LANs,
except they have more restrictions on them. They let students communicate with
each other as well as the administration.
There are two major types of network architectures at the
moment. The first model connects computers with each other without the need for
an intermediary computer. This is known as the peer to peer style of
networking. This tutorial explains peer to peer networks in more detail. The
other model relies on a server to act as an intermediary between the network
computers. This is known as the client server architecture model.
Categories of Network:
Network can be divided in to two main
categories:
- Peer-to-peer.
- Server – based.
In peer-to-peer
networking there are no dedicated servers or hierarchy among the computers. All
of the computers are equal and therefore known as peers. Normally each computer
serves as Client/Server and there is no one assigned to be an administrator responsible
for the entire network.Peer-to-peer networks are good choices for needs of small organizations where the users are allocated in the same general area, security is not an issue and the organization and the network will have limited growth within the foreseeable future.
The term Client/server refers to the concept of sharing the work involved in processing data between the client computer and the most powerful server computer..
The client/server network is
the most efficient way to provide:
- Databases and management of applications such as
Spreadsheets, Accounting, Communications and Document management.
- Network management.
- Centralized file storage.
The client/server
model is basically an implementation of distributed or cooperative processing.
At the heart of the model is the concept of splitting application functions
between a client and a server processor. The division of labor between the
different processors enables the application designer to place an application
function on the processor that is most appropriate for that function. This lets
the software designer optimize the use of processors--providing the greatest
possible return on investment for the hardware.
Client/server application design also lets the application provider mask the actual location of application function. The user often does not know where a specific operation is executing. The entire function may execute in either the PC or server, or the function may be split between them. This masking of application function locations enables system implementers to upgrade portions of a system over time with a minimum disruption of application operations, while protecting the investment in existing hardware and software.
Client/server application design also lets the application provider mask the actual location of application function. The user often does not know where a specific operation is executing. The entire function may execute in either the PC or server, or the function may be split between them. This masking of application function locations enables system implementers to upgrade portions of a system over time with a minimum disruption of application operations, while protecting the investment in existing hardware and software.
The
OSI Model:
Open System
Interconnection (OSI) reference
model has become an International standard and serves as a guide for
networking. This model is the best known and most widely used guide to describe
networking environments. Vendors design network products based on the
specifications of the OSI model. It provides a description of how network
hardware and software work together in a layered fashion to make communications
possible. It also helps with trouble shooting by providing a frame of reference
that describes how components are supposed to function.There are seven to get familiar with and these are the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and the application layer.
- Physical
Layer, is just that the physical parts of the network such
as wires, cables, and there media along with the length. Also this layer
takes note of the electrical signals that transmit data throughout system.
- Data
Link Layer, this layer is where we actually assign meaning
to the electrical signals in the network. The layer also determines the
size and format of data sent to printers, and other devices. Also I don't
want to forget that these are also called nodes in the network. Another
thing to consider in this layer is will also allow and define the error
detection and correction schemes that insure data was sent and received.
- Network
Layer, this
layer provides the definition for the connection of two dissimilar
networks.
- Transport Layer, this layer allows data to be
broken into smaller packages for data to be distributed and addressed to
other nodes (workstations).
- Session
Layer, this layer helps out with the task to carry
information from one node (workstation) to another node (workstation). A
session has to be made before we can transport information to another
computer.
- Presentation
Layer, this layer is responsible to code and decode data
sent to the node.
- Application
Layer, this layer allows you to use an application that will
communicate with say the operation system of a server. A good example
would be using your web browser to interact with the operating system on a
server such as Windows NT, which in turn gets the data you requested.
Network
Architectures:
Ethernet
Ethernet is
the most popular physical layer LAN technology in use today. Other LAN types include Token
Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous
Transfer Mode (ATM) and LocalTalk. Ethernet connection is popular because it
strikes a good balance between speed, cost and ease of installation. These
benefits, combined with wide acceptance in the computer marketplace and the
ability to support virtually all popular network protocols, make Ethernet an
ideal networking technology for most computer users today. The Institute for
Electrical and Electronic Engineers (IEEE) defines the Ethernet standard as
IEEE Standard 802.3. This standard defines rules for configuring an Ethernet
network as well as specifying how elements in an Ethernet network interact with
one another. By adhering to the IEEE standard, network equipment and network
protocols can communicate efficiently.
Fast Ethernet
For Ethernet networks that need higher transmission
speeds, the Fast Ethernet standard (IEEE 802.3u) has been established. This standard raises the Ethernet speed limit from 10
Megabits per second (Mbps) to 100 Mbps with only minimal changes to the
existing cable structure. There are three types of Fast Ethernet: 100BASE-TX
for use with level 5 UTP cable, 100BASE-FX for use with fiber-optic cable, and
100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable.
The 100BASE-TX standard has become the most popular due to its close
compatibility with the 10BASE-T Ethernet standard. For the network manager, the
incorporation of Fast Ethernet into an existing configuration presents a host
of decisions. Managers must determine the number of users in each site on the
network that need the higher throughput, decide which segments of the backbone
need to be reconfigured specifically for 100BASE-T and then choose the
necessary hardware to connect the 100BASE-T segments with existing 10BASE-T
segments. Gigabit Ethernet is a future technology that promises a migration
path beyond Fast Ethernet so the next generation of networks will support even
higher data transfer speeds.
Token Ring
Token Ring is another form of network configuration which differs
from Ethernet in that all messages are transferred in a unidirectional manner
along the ring at all times. Data is transmitted in tokens, which are passed
along the ring and viewed by each device. When a device sees a message
addressed to it, that device copies the message and then marks that message as
being read. As the message makes its way along the ring, it eventually gets
back to the sender who now notes that the message was received by the intended
device. The sender can then remove the message and free that token for use by
others.
Various PC vendors have been proponents of Token Ring networks at different times and thus these types of networks have been implemented in many organizations.
Various PC vendors have been proponents of Token Ring networks at different times and thus these types of networks have been implemented in many organizations.
FDDI
FDDI (Fiber-Distributed Data Interface) is a standard for data transmission on fiber optic lines
in a local area network that can extend in range up to 200 km (124 miles). The
FDDI protocol is based on the token ring protocol. In addition to being large
geographically, an FDDI local area network can support thousands of users.
Protocols:
Network protocols are standards that allow computers to
communicate. A
protocol defines how computers identify one another on a network, the form that
the data should take in transit, and how this information is processed once it
reaches its final destination. Protocols also define procedures for handling
lost or damaged transmissions or "packets." TCP/IP (for UNIX, Windows
NT, Windows 95 and other platforms), IPX (for Novell NetWare), DECnet (for
networking Digital Equipment Corp. computers), AppleTalk (for Macintosh
computers), and NetBIOS/NetBEUI (for LAN Manager and Windows NT networks) are
the main types of network protocols in use today.
Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence,"
Some Important Protocols and their job:
Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence,"
Some Important Protocols and their job:
|
Protocol
|
Acronym
|
Its Job
|
|
Point-To-Point
|
TCP/IP
|
The backbone
protocol of the internet. Popular also for intranets using the internet
|
|
Transmission Control
Protocol/internet Protocol
|
TCP/IP
|
The backbone
protocol of the internet. Popular also for intranets using the internet
|
|
Internetwork Package
Exchange/Sequenced Packet Exchange
|
IPX/SPX
|
This is a standard
protocol for Novell Network Operating System
|
|
NetBIOS Extended
User Interface
|
NetBEUI
|
This is a Microsoft
protocol that doesn't support routing to other networks
|
|
File Transfer
Protocol
|
FTP
|
Used to send and
receive files from a remote host
|
|
Hyper Text Transfer
Protocol
|
HTTP
|
Used for the web to
send documents that are encoded in HTML.
|
|
Network File
Services
|
NFS
|
Allows network nodes
or workstations to access files and drives as if they were their own.
|
|
Simple Mail Transfer
Protocol
|
SMTP
|
Used to send Email
over a network
|
|
Telnet
|
|
Used to connect to a
host and emulate a terminal that the remote server can recognize
|
Introduction to TCP/IP
Networks:
TCP/IP-based networks play an increasingly important role in
computer networks. Perhaps one
reason for their appeal is that they are based on an open specification that is
not controlled by any vendor.
What Is TCP/IP?
TCP stands for Transmission Control Protocol and IP stands for
Internet Protocol. The
term TCP/IP is not limited just to these two protocols, however. Frequently,
the term TCP/IP is used to refer to a group of protocols related to the TCP and
IP protocols such as the User Datagram Protocol (UDP), File Transfer Protocol
(FTP), Terminal Emulation Protocol (TELNET), and so on.
The Origins of TCP/IP
In
the late 1960s, DARPA (the Defense Advanced Research Project Agency), in the
United States, noticed that there was a rapid proliferation of computers in
military communications. Computers, because they can be easily programmed,
provide flexibility in achieving network functions that is not available with
other types of communications equipment. The computers then used in military
communications were manufactured by different vendors and were designed to
interoperate with computers from that vendor only. Vendors used proprietary
protocols in their communications equipment. The military had a multi vendor
network but no common protocol to support the heterogeneous equipment from
different vendors
Network Cables and Stuff:
In
the network you will commonly find three types of cables used these are the,
coaxial cable, fiber optic and twisted pair.
Thick Coaxial
Cable
This type cable is usually yellow in color and used in
what is called thicknets, and has two conductors. This coax can be used in
500-meter lengths. The cable itself is made up of a solid center wire with a
braided metal shield and plastic sheathing protecting the rest of the wire.
Thin Coaxial Cable
As with the thick coaxial cable is used in thicknets the
thin version is used in thinnets. This type cable is also used called or
referred to as RG-58. The cable is really just a cheaper version of the thick
cable.
Fiber Optic Cable
As we all know fiber optics are pretty darn cool and not
cheap. This cable is smaller and can carry a vast amount of information fast
and over long distances.
Twisted Pair Cables
These come in two flavors of unshielded and shielded.
Shielded Twisted Pair (STP)
Is more common in high-speed networks. The biggest
difference you will see in the UTP and STP is that the STP use's metallic
shield wrapping to protect the wire from interference.
-Something else to note about these cables is that they are defined in numbers also. The bigger the number the better the protection from interference. Most networks should go with no less than a CAT 3 and CAT 5 is most recommended.
-Now you know about cables we need to know about connectors. This is pretty important and you will most likely need the RJ-45 connector. This is the cousin of the phone jack connector and looks real similar with the exception that the RJ-45 is bigger. Most commonly your connector are in two flavors and this is BNC (Bayonet Naur Connector) used in thicknets and the RJ-45 used in smaller networks using UTP/STP.
-Something else to note about these cables is that they are defined in numbers also. The bigger the number the better the protection from interference. Most networks should go with no less than a CAT 3 and CAT 5 is most recommended.
-Now you know about cables we need to know about connectors. This is pretty important and you will most likely need the RJ-45 connector. This is the cousin of the phone jack connector and looks real similar with the exception that the RJ-45 is bigger. Most commonly your connector are in two flavors and this is BNC (Bayonet Naur Connector) used in thicknets and the RJ-45 used in smaller networks using UTP/STP.
Unshielded Twisted Pair (UTP)
This is the most popular form of cables in the network
and the cheapest form that you can go with. The UTP has four pairs of wires and
all inside plastic sheathing. The biggest reason that we call it Twisted Pair
is to protect the wires from interference from themselves. Each wire is only
protected with a thin plastic sheath.
Ethernet Cabling
Now to familiarize you with more on the Ethernet and it's
cabling we need to look at the 10's. 10Base2, is considered the thin Ethernet,
thinnet, and thinwire which uses light coaxial cable to create a 10 Mbps
network. The cable segments in this network can't be over 185 meters in length.
These cables connect with the BNC connector. Also as a note these unused
connection must have a terminator, which will be a 50-ohm terminator.
10Base5, this is considered a thicknet and is used with coaxial cable arrangement such as the BNC connector. The good side to the coaxial cable is the high-speed transfer and cable segments can be up to 500 meters between nodes/workstations. You will typically see the same speed as the 10Base2 but larger cable lengths for more versatility.
10BaseT, the “T” stands for twisted as in UTP (Unshielded Twisted Pair) and uses this for 10Mbps of transfer. The down side to this is you can only have cable lengths of 100 meters between nodes/workstations. The good side to this network is they are easy to set up and cheap! This is why they are so common an ideal for small offices or homes.
100BaseT, is considered Fast Ethernet uses STP (Shielded Twisted Pair) reaching data transfer of 100Mbps. This system is a little more expensive but still remains popular as the 10BaseT and cheaper than most other type networks. This on of course would be the cheap fast version.
10BaseF, this little guy has the advantage of fiber optics and the F stands for just that. This arrangement is a little more complicated and uses special connectors and NIC's along with hubs to create its network. Pretty darn neat and not to cheap on the wallet.
An important part of designing and installing an Ethernet is selecting the appropriate Ethernet medium. There are four major types of media in use today: Thickwire for 10BASE5 networks, thin coax for 10BASE2 networks, unshielded twisted pair (UTP) for 10BASE-T networks and fiber optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL) networks. This wide variety of media reflects the evolution of Ethernet and also points to the technology's flexibility. Thickwire was one of the first cabling systems used in Ethernet but was expensive and difficult to use. This evolved to thin coax, which is easier to work with and less expensive.
10Base5, this is considered a thicknet and is used with coaxial cable arrangement such as the BNC connector. The good side to the coaxial cable is the high-speed transfer and cable segments can be up to 500 meters between nodes/workstations. You will typically see the same speed as the 10Base2 but larger cable lengths for more versatility.
10BaseT, the “T” stands for twisted as in UTP (Unshielded Twisted Pair) and uses this for 10Mbps of transfer. The down side to this is you can only have cable lengths of 100 meters between nodes/workstations. The good side to this network is they are easy to set up and cheap! This is why they are so common an ideal for small offices or homes.
100BaseT, is considered Fast Ethernet uses STP (Shielded Twisted Pair) reaching data transfer of 100Mbps. This system is a little more expensive but still remains popular as the 10BaseT and cheaper than most other type networks. This on of course would be the cheap fast version.
10BaseF, this little guy has the advantage of fiber optics and the F stands for just that. This arrangement is a little more complicated and uses special connectors and NIC's along with hubs to create its network. Pretty darn neat and not to cheap on the wallet.
An important part of designing and installing an Ethernet is selecting the appropriate Ethernet medium. There are four major types of media in use today: Thickwire for 10BASE5 networks, thin coax for 10BASE2 networks, unshielded twisted pair (UTP) for 10BASE-T networks and fiber optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL) networks. This wide variety of media reflects the evolution of Ethernet and also points to the technology's flexibility. Thickwire was one of the first cabling systems used in Ethernet but was expensive and difficult to use. This evolved to thin coax, which is easier to work with and less expensive.
Network Topologies:
What is a Network topology?
A network topology is the geometric arrangement of nodes
and cable links in a LAN,
There are three topology's to think about when you get into networks. These are the star, rind, and the bus.
Star, in a star topology each node has a dedicated set of wires connecting it to a central network hub. Since all traffic passes through the hub, the hub becomes a central point for isolating network problems and gathering network statistics.
Ring, a ring topology features a logically closed loop. Data packets travel in a single direction around the ring from one network device to the next. Each network device acts as a repeater, meaning it regenerates the signal
Bus, the bus topology, each node (computer, server, peripheral etc.) attaches directly to a common cable. This topology most often serves as the backbone for a network. In some instances, such as in classrooms or labs, a bus will connect small workgroups
There are three topology's to think about when you get into networks. These are the star, rind, and the bus.
Star, in a star topology each node has a dedicated set of wires connecting it to a central network hub. Since all traffic passes through the hub, the hub becomes a central point for isolating network problems and gathering network statistics.
Ring, a ring topology features a logically closed loop. Data packets travel in a single direction around the ring from one network device to the next. Each network device acts as a repeater, meaning it regenerates the signal
Bus, the bus topology, each node (computer, server, peripheral etc.) attaches directly to a common cable. This topology most often serves as the backbone for a network. In some instances, such as in classrooms or labs, a bus will connect small workgroups
Collisions:
Ethernet is a shared media, so there are rules for
sending packets of data to avoid conflicts and protect data integrity. Nodes
determine when the network is available for sending packets. It is possible
that two nodes at different locations attempt to send data at the same time.
When both PCs are transferring a packet to the network at the same time, a
collision will result.
Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users on the network, which results in a lot of contention for network bandwidth. This can slow the performance of the network from the user's point of view. Segmenting the network, where a network is divided into different pieces joined together logically with a bridge or switch, is one way of reducing an overcrowded network.
Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users on the network, which results in a lot of contention for network bandwidth. This can slow the performance of the network from the user's point of view. Segmenting the network, where a network is divided into different pieces joined together logically with a bridge or switch, is one way of reducing an overcrowded network.
Ethernet Products:
The standards and technology that have just been
discussed help define the specific products that network managers use to build
Ethernet networks. The following text discusses the key products needed to
build an Ethernet LAN.
Transceivers
Transceivers are used to connect nodes to the various Ethernet media.
Most computers and network interface cards contain a built-in 10BASE-T or
10BASE2 transceiver, allowing them to be connected directly to Ethernet without
requiring an external transceiver. Many Ethernet devices provide an AUI
connector to allow the user to connect to any media type via an external
transceiver. The AUI connector consists of a 15-pin D-shell type connector,
female on the computer side, male on the transceiver side. Thickwire (10BASE5)
cables also use transceivers to allow connections.
For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices.
For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices.
Network Interface Cards:
Network interface cards, commonly referred to as NICs, and are used to connect a
PC to a network. The NIC provides a physical connection between the networking
cable and the computer's internal bus. Different computers have different bus
architectures; PCI bus master slots are most commonly found on 486/Pentium PCs
and ISA expansion slots are commonly found on 386 and older PCs. NICs come in
three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number of bits
that can be transferred to the NIC, the faster the NIC can transfer data to the
network cable.
Many NIC adapters comply with Plug-n-Play specifications. On these systems, NICs are automatically configured without user intervention, while on non-Plug-n-Play systems, configuration is done manually through a setup program and/or DIP switches.
Cards are available to support almost all networking standards, including the latest Fast Ethernet environment. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Full duplex networking is another option, where a dedicated connection to a switch allows a NIC to operate at twice the speed.
Many NIC adapters comply with Plug-n-Play specifications. On these systems, NICs are automatically configured without user intervention, while on non-Plug-n-Play systems, configuration is done manually through a setup program and/or DIP switches.
Cards are available to support almost all networking standards, including the latest Fast Ethernet environment. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Full duplex networking is another option, where a dedicated connection to a switch allows a NIC to operate at twice the speed.
Hubs/Repeaters:
Hubs/repeaters are used to connect together two or more Ethernet segments of
any media type. In larger designs, signal quality begins to deteriorate as
segments exceed their maximum length. Hubs provide the signal amplification
required to allow a segment to be extended a greater distance. A hub takes any
incoming signal and repeats it out all ports.
Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later.
Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later.
|
Network Type
|
Max Nodes
Per Segment |
Max Distance
Per Segment |
|
10BASE-T
10BASE2 10BASE5 10BASE-FL |
2
30 100 2 |
100m
185m 500m 2000m |
Adding Speed:
While
repeaters allow LANs to extend beyond normal distance limitations, they still
limit the number of nodes that can be supported. Bridges and switches, however,
allow LANs to grow significantly larger by virtue of their ability to support
full Ethernet segments on each port. Additionally, bridges and switches
selectively filter network traffic to only those packets needed on each segment
- this significantly increases throughput on each segment and on the overall
network. By providing better performance and more flexibility for network
topologies, bridges and switches will continue to gain popularity among network
managers.
Bridges:
The
function of a bridge is to connect separate networks together. Bridges connect
different networks types (such as Ethernet and Fast Ethernet) or networks of
the same type. Bridges map the Ethernet addresses of the nodes residing on each
network segment and allow only necessary traffic to pass through the bridge.
When a packet is received by the bridge, the bridge determines the destination
and source segments. If the segments are the same, the packet is dropped
("filtered"); if the segments are different, then the packet is
"forwarded" to the correct segment. Additionally, bridges do not
forward bad or misaligned packets.
Bridges are also called "store-and-forward" devices because they look at the whole Ethernet packet before making filtering or forwarding decisions. Filtering packets, and regenerating forwarded packets enable bridging technology to split a network into separate collision domains. This allows for greater distances and more repeaters to be used in the total network design.
Bridges are also called "store-and-forward" devices because they look at the whole Ethernet packet before making filtering or forwarding decisions. Filtering packets, and regenerating forwarded packets enable bridging technology to split a network into separate collision domains. This allows for greater distances and more repeaters to be used in the total network design.
Ethernet Switches:
Ethernet switches are an expansion of the concept in Ethernet bridging. LAN
switches can link four, six, ten or more networks together, and have two basic
architectures: cut-through and store-and-forward. In the past, cut-through
switches were faster because they examined the packet destination address only
before forwarding it on to its destination segment. A store-and-forward switch,
on the other hand, accepts and analyzes the entire packet before forwarding it
to its destination.
It takes more time to examine the entire packet, but it allows the switch to catch certain packet errors and keep them from propagating through the network. Both cut-through and store-and-forward switches separate a network into collision domains, allowing network design rules to be extended. Each of the segments attached to an Ethernet switch has a full 10 Mbps of bandwidth shared by fewer users, which results in better performance (as opposed to hubs that only allow bandwidth sharing from a single Ethernet). Newer switches today offer high-speed links, FDDI, Fast Ethernet or ATM. These are used to link switches together or give added bandwidth to high-traffic servers. A network composed of a number of switches linked together via uplinks is termed a "collapsed backbone" network.
It takes more time to examine the entire packet, but it allows the switch to catch certain packet errors and keep them from propagating through the network. Both cut-through and store-and-forward switches separate a network into collision domains, allowing network design rules to be extended. Each of the segments attached to an Ethernet switch has a full 10 Mbps of bandwidth shared by fewer users, which results in better performance (as opposed to hubs that only allow bandwidth sharing from a single Ethernet). Newer switches today offer high-speed links, FDDI, Fast Ethernet or ATM. These are used to link switches together or give added bandwidth to high-traffic servers. A network composed of a number of switches linked together via uplinks is termed a "collapsed backbone" network.
Routers:
Routers filter out network traffic by specific protocol rather than by
packet address. Routers also divide networks logically instead of physically.
An IP router can divide a network into various subnets so that only traffic
destined for particular IP addresses can pass between segments. Network speed
often decreases due to this type of intelligent forwarding. Such filtering
takes more time than that exercised in a switch or bridge, which only looks at
the Ethernet address. However, in more complex networks, overall efficiency is
improved by using routers.
What is a network firewall?
A
firewall is a system or group of systems that enforces an access control policy
between two networks. The actual means by which this is accomplished varies
widely, but in principle, the firewall can be thought of as a pair of
mechanisms: one which exists to block traffic, and the other which exists to
permit traffic. Some firewalls place a greater emphasis on blocking traffic,
while others emphasize permitting traffic. Probably the most important thing to
recognize about a firewall is that it implements an access control policy. If
you don't have a good idea of what kind of access you want to allow or to deny,
a firewall really won't help you. It's also important to recognize that the firewall's
configuration, because it is a mechanism for enforcing policy, imposes its
policy on everything behind it. Administrators for firewalls managing the
connectivity for a large number of hosts therefore have a heavy responsibility.
Network Design Criteria:
Ethernets
and Fast Ethernets have design rules that must be followed in order to function
correctly. Maximum number of nodes, number of repeaters and maximum segment
distances are defined by the electrical and mechanical design properties of
each type of Ethernet and Fast Ethernet media.
A network using repeaters, for instance, functions with the timing constraints of Ethernet. Although electrical signals on the Ethernet media travel near the speed of light, it still takes a finite time for the signal to travel from one end of a large Ethernet to another. The Ethernet standard assumes it will take roughly 50 microseconds for a signal to reach its destination.
Ethernet is subject to the "5-4-3" rule of repeater placement: the network can only have five segments connected; it can only use four repeaters; and of the five segments, only three can have users attached to them; the other two must be inter-repeater links.
If the design of the network violates these repeater and placement rules, then timing guidelines will not be met and the sending station will resend that packet. This can lead to lost packets and excessive resent packets, which can slow network performance and create trouble for applications. Fast Ethernet has modified repeater rules, since the minimum packet size takes less time to transmit than regular Ethernet. The length of the network links allows for a fewer number of repeaters. In Fast Ethernet networks, there are two classes of repeaters. Class I repeaters have a latency of 0.7 microseconds or less and are limited to one repeater per network. Class II repeaters have a latency of 0.46 microseconds or less and are limited to two repeaters per network. The following are the distance (diameter) characteristics for these types of Fast Ethernet repeater combinations:
A network using repeaters, for instance, functions with the timing constraints of Ethernet. Although electrical signals on the Ethernet media travel near the speed of light, it still takes a finite time for the signal to travel from one end of a large Ethernet to another. The Ethernet standard assumes it will take roughly 50 microseconds for a signal to reach its destination.
Ethernet is subject to the "5-4-3" rule of repeater placement: the network can only have five segments connected; it can only use four repeaters; and of the five segments, only three can have users attached to them; the other two must be inter-repeater links.
If the design of the network violates these repeater and placement rules, then timing guidelines will not be met and the sending station will resend that packet. This can lead to lost packets and excessive resent packets, which can slow network performance and create trouble for applications. Fast Ethernet has modified repeater rules, since the minimum packet size takes less time to transmit than regular Ethernet. The length of the network links allows for a fewer number of repeaters. In Fast Ethernet networks, there are two classes of repeaters. Class I repeaters have a latency of 0.7 microseconds or less and are limited to one repeater per network. Class II repeaters have a latency of 0.46 microseconds or less and are limited to two repeaters per network. The following are the distance (diameter) characteristics for these types of Fast Ethernet repeater combinations:
|
Fast Ethernet
|
Copper
|
Fiber
|
|
No Repeaters
One Class I Repeater One Class II Repeater Two Class II Repeaters |
100m
200m 200m 205m |
412m*
272m 272m 228m |
* Full Duplex Mode 2 km
When conditions require greater distances or an increase in the number of nodes/repeaters, then a bridge, router or switch can be used to connect multiple networks together. These devices join two or more separate networks, allowing network design criteria to be restored. Switches allow network designers to build large networks that function well. The reduction in costs of bridges and switches reduces the impact of repeater rules on network design.
Each network connected via one of these devices is referred to as a separate collision domain in the overall network.
Types of
Servers:
Device Servers
A device server is defined as a specialized, network-based hardware
device designed to perform a single or specialized set of server functions. It
is characterized by a minimal operating architecture that requires no per seat
network operating system license, and client access that is independent of any
operating system or proprietary protocol. In addition the device server is a
"closed box," delivering extreme ease of installation, minimal
maintenance, and can be managed by the client remotely via a Web browser.
Print servers, terminal servers, remote access servers and network time servers are examples of device servers which are specialized for particular functions. Each of these types of servers has unique configuration attributes in hardware or software that help them to perform best in their particular arena.
Print servers, terminal servers, remote access servers and network time servers are examples of device servers which are specialized for particular functions. Each of these types of servers has unique configuration attributes in hardware or software that help them to perform best in their particular arena.
Print Servers
Print servers allow printers to be shared by other users on the
network. Supporting either parallel and/or serial interfaces, a print server
accepts print jobs from any person on the network using supported protocols and
manages those jobs on each appropriate printer.
Print servers generally do not contain a large amount of memory; printers simply store information in a queue. When the desired printer becomes available, they allow the host to transmit the data to the appropriate printer port on the server. The print server can then simply queue and print each job in the order in which print requests are received, regardless of protocol used or the size of the job.
Print servers generally do not contain a large amount of memory; printers simply store information in a queue. When the desired printer becomes available, they allow the host to transmit the data to the appropriate printer port on the server. The print server can then simply queue and print each job in the order in which print requests are received, regardless of protocol used or the size of the job.
Multiport Device Servers
Devices that are attached to a network through a
multiport device server can be shared between terminals and hosts at both the
local site and throughout the network. A single terminal may be connected to
several hosts at the same time (in multiple concurrent sessions), and can
switch between them. Multiport device servers are also used to network devices
that have only serial outputs. A connection between serial ports on different
servers is opened, allowing data to move between the two devices.
Given its natural translation ability, a multi-protocol multiport device server can perform conversions between the protocols it knows, like LAT and TCP/IP. While server bandwidth is not adequate for large file transfers, it can easily handle host-to-host inquiry/response applications, electronic mailbox checking, etc. And it is far more economical than the alternatives of acquiring expensive host software and special-purpose converters. Multiport device and print servers give their users greater flexibility in configuring and managing their networks.
Whether it is moving printers and other peripherals from one network to another, expanding the dimensions of interoperability or preparing for growth, multiport device servers can fulfill your needs, all without major rewiring.
Given its natural translation ability, a multi-protocol multiport device server can perform conversions between the protocols it knows, like LAT and TCP/IP. While server bandwidth is not adequate for large file transfers, it can easily handle host-to-host inquiry/response applications, electronic mailbox checking, etc. And it is far more economical than the alternatives of acquiring expensive host software and special-purpose converters. Multiport device and print servers give their users greater flexibility in configuring and managing their networks.
Whether it is moving printers and other peripherals from one network to another, expanding the dimensions of interoperability or preparing for growth, multiport device servers can fulfill your needs, all without major rewiring.
Access Servers
While Ethernet is limited to a geographic area, remote
users such as traveling sales people need access to network-based resources.
Remote LAN access, or remote access, is a popular way to provide this
connectivity. Access servers use telephone services to link a user or office
with an office network. Dial-up remote access solutions such as ISDN or
asynchronous dial introduce more flexibility. Dial-up remote access offers both
the remote office and the remote user the economy and flexibility of "pay
as you go" telephone services. ISDN is a special telephone service that
offers three channels, two 64 Kbps "B" channels for user data and a
"D" channel for setting up the connection. With ISDN, the B channels
can be combined for double bandwidth or separated for different applications or
users. With asynchronous remote access, regular telephone lines are combined
with modems and remote access servers to allow users and networks to dial
anywhere in the world and have data access. Remote access servers provide
connection points for both dial-in and dial-out applications on the network to
which they are attached. These hybrid devices route and filter protocols and
offer other services such as modem pooling and terminal/printer services. For the
remote PC user, one can connect from any available telephone jack (RJ45),
including those in a hotel rooms or on most airplanes.
Network Time Servers
A network time server is a server specialized in the
handling of timing information from sources such as satellites or radio
broadcasts and is capable of providing this timing data to its attached
network. Specialized protocols such as NTP or udp/time allow a time server to
communicate to other network nodes ensuring that activities that must be
coordinated according to their time of execution are synchronized correctly.
GPS satellites are one source of information that can allow global
installations to achieve constant timing.
IP Addressing:
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" notation.
Example: 140.179.220.200
It is sometimes useful to view the values in their binary form.
140 .179 .220 .200
10001100.10110011.11011100.11001000
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.
Example: 140.179.220.200
It is sometimes useful to view the values in their binary form.
140 .179 .220 .200
10001100.10110011.11011100.11001000
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.
Address Classes:
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 decimal.
Class C addresses begin with 110x, or 192 to 223 decimal.
Class D addresses begin with 1110, or 224 to 239 decimal.
Class E addresses begin with 1111, or 240 to 254 decimal.
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, 140.179.220.200 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, 140.179.0.0 specifies the network address for 140.179.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 140.179.255.255 specifies the example broadcast address. Note that this is true regardless of the length of the node section.
Class A addresses begin with 0xxx, or 1 to 126 decimal.
Class B addresses begin with 10xx, or 128 to 191 decimal.
Class C addresses begin with 110x, or 192 to 223 decimal.
Class D addresses begin with 1110, or 224 to 239 decimal.
Class E addresses begin with 1111, or 240 to 254 decimal.
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, 140.179.220.200 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, 140.179.0.0 specifies the network address for 140.179.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 140.179.255.255 specifies the example broadcast address. Note that this is true regardless of the length of the node section.
Private Subnets:
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 receive.
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 receive.
Subnet Masking
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:
10001100.10110011.11110000.11001000 140.179.240.200 Class B IP Address
11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask
10001100.10110011.00000000.00000000 140.179.000.000 Network Address
For example, using our test IP address and the default Class B subnet mask, we get:
10001100.10110011.11110000.11001000 140.179.240.200 Class B IP Address
11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask
10001100.10110011.00000000.00000000 140.179.000.000 Network Address
Default subnet masks:
Class A - 255.0.0.0 - 11111111.00000000.00000000.00000000
Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000
Class C - 255.255.255.0 - 11111111.11111111.11111111.00000000
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
Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000
Class C - 255.255.255.0 - 11111111.11111111.11111111.00000000
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
Examining your network with commands:
Ping
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.
Sample ping session
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=4 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=5 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=6 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=7 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=8 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=9 ttl=255 time=2 ms
localhost ping statistics
10 packets transmitted, 10 packets received, 0% packet loss
round-trip min/avg/max = 2/2/2 ms
meikro$
The Time To Live (TTL) field can be interesting. The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." But for us, it provides additional information. We can use the TTL to determine approximately how many router hops the packet has gone through. In this case it's 255 minus N hops, where N is the TTL of the returning Echo Replies. If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes, which isn't a great thing.
The time field is an indication of the round-trip time to get a packet to the remote host. The reply is measured in milliseconds. In general, it's best if round-trip times are under 200 milliseconds. The time it takes a packet to reach its destination is called latency. If you see a large variance in the round-trip times (which is called "jitter"), you are going to see poor performance talking to the host
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.
Sample ping session
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=4 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=5 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=6 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=7 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=8 ttl=255 time=2 ms
64 bytes from 127.0.0.1: icmp_seq=9 ttl=255 time=2 ms
localhost ping statistics
10 packets transmitted, 10 packets received, 0% packet loss
round-trip min/avg/max = 2/2/2 ms
meikro$
The Time To Live (TTL) field can be interesting. The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." But for us, it provides additional information. We can use the TTL to determine approximately how many router hops the packet has gone through. In this case it's 255 minus N hops, where N is the TTL of the returning Echo Replies. If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes, which isn't a great thing.
The time field is an indication of the round-trip time to get a packet to the remote host. The reply is measured in milliseconds. In general, it's best if round-trip times are under 200 milliseconds. The time it takes a packet to reach its destination is called latency. If you see a large variance in the round-trip times (which is called "jitter"), you are going to see poor performance talking to the host
NSLOOKUP
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.
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
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 responsive.
IPconfig
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.
Windows 2000 IP Configuration
Host Name . . . . . . . . . . . . : cowder
Primary DNS Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . :
WAN (PPP/SLIP) Interface
Physical Address. . . . . . . . . : 00-53-45-00-00-00
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 12.90.108.123
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . : 12.90.108.125
DNS Servers . . . . . . . . . . . : 12.102.244.2
204.127.129.2
This command when used with the /all switch, reveal enormous amounts of troubleshooting information within the system.
Windows 2000 IP Configuration
Host Name . . . . . . . . . . . . : cowder
Primary DNS Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . :
WAN (PPP/SLIP) Interface
Physical Address. . . . . . . . . : 00-53-45-00-00-00
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 12.90.108.123
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . : 12.90.108.125
DNS Servers . . . . . . . . . . . : 12.102.244.2
204.127.129.2
Hi. I’m Designer of Blog Magic. I’m CEO/Founder of ThemeXpose. I’m Creative Art Director, Web Designer, UI/UX Designer, Interaction Designer, Industrial Designer, Web Developer, Business Enthusiast, StartUp Enthusiast, Speaker, Writer and Photographer. Inspired to make things looks better.
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