BASIC PRINCIPLES OF NETWORKS

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COMPUTER NETWORK PROTOCOL

ASSIGNMENT - I

SUBMITTED BY

R.JAYA PRAKASH M.TECH – NIE
PONDICHERRY UNIVERSITY.

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BASIC PRINCIPLES OF NETWORKS

NETWORK

A computer network is the infrastructure which allows two or more
computers to communicate with each other.

TYPES OF NETWORKS

On the basis of scale there are five types of networks; they are:

LOCAL AREA NETWORK

Local Area Network, generally called LAN’s are privately-owned
networks within a single building or campus of up to a few kilometers in size.
They are widely used to connect personal computers and workstations in
company offices and factories to share resources and exchange information.
 LANs are restricted in size.
 Traditional LANs run at speed of 10 Mbps to 100Mbps.
 Newer LANs operate at up to 10 Gbps.

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WIDE AREA NETWORK

 A Wide Area Network, or WAN, spans a large geographical area often a
country or continent.

 It contains a collection of machines intended for running user programs.

 The hosts are connected by a communication subnet, or just subnet for short.

 The hosts are owned by customers whereas the communication subnet is
typically owned and operated by a telephone company or internet service
provider.

 The defining characteristics of LANs, in contrast to WANs (Wide Area
Networks), include their higher data transfer rates, smaller geographic range,
and lack of a need for leased telecommunication lines.

METROPOLITAN AREA NETWORK

 A Metropolitan Area Network (man) is a network that connects two or more
local area networks or campus area networks together but does not extend

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beyond the boundaries of the immediate town/city. routers, switches and
hubs are connected to create a metropolitan area network.

PERSONAL AREA NETWORK

 A personal area network (PAN) is a computer network used for
communication among computer devices close to one person.

 Some examples of devices that are used in a PAN are personal computers,
printers, fax machines, telephones, PDAs, scanners, and even video game
consoles. Such a PAN may include wired and wireless connections between
devices.

 The reach of a PAN is typically at least about 20-30 feet (approximately 6-9
meters), but this is expected to increase with technology improvements.

VIRTUAL PRIVATE NETWORK

 A virtual private network (VPN) is a computer network in which some of the
links between nodes are carried by open connections or virtual circuits in
some larger network (e.g., the Internet) instead of by physical wires.

 A VPN may have best-effort performance, or may have a defined service
level agreement (SLA) between the VPN customer and the VPN service

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provider. Generally, a VPN has a topology more complex than point-to-
point.

 A VPN allows computer users to appear to be editing from an IP address
location other than the one which connects the actual computer to the
Internet.

GLOBAL AREA NETWORK:

 A global area networks (GAN) specification is in development by several
groups, and there is no common definition. In general, however, a GAN is a
model for supporting mobile communications across an arbitrary number of
wireless LANs, satellite coverage areas, etc.

 The key challenge in mobile communications is "handing off" the user
communications from one local coverage area to the next. In IEEE Project
802, this involves a succession of terrestrial WIRELESS local area networks
(WLAN).

NETWORK TOPOLOGY

The specific arrangement of the elements of a network. IS CALLED
topology.

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Network topologies are categorized into the following basic types:

 BUS
 RING
 STAR
 TREE
 MESH

BUS TOPOLOGY

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FIG.3 BUS TOPOLOGY

 Bus networks (not to be confused with the system bus of a computer) use a
common backbone to connect all devices.

 A single cable, the backbone functions as a shared communication medium
that devices attach or tap into with an interface connector.

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 A device wanting to communicate with another device on the network sends
a broadcast message onto the wire that all other devices see, but only the
intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling
compared to the alternatives.

10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet
cabling options many years ago for bus topologies.

However, bus networks work best with a limited number of devices.

If more than a few dozen computers are added to a network bus, performance
problems will likely result.

In addition, if the backbone cable fails, the entire network effectively becomes
unusable.

RING TOPOLOGY

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FIG.4 RING TOPOLOGY

In a ring network, every device has exactly two neighbors for
communication purposes. All messages travel through a ring in the same direction
(either "clockwise" or "counterclockwise"). A failure in any cable or device breaks
the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token
Ring technology. Ring topologies are found in some office buildings or school
campuses.

STAR TOPOLOGY

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FIG.5. STAR TOPOLOGY
Many home networks use the star topology. A star network features a central
connection point called a "hub" that may be a hub, switch or router. Devices
typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable,
but a failure in any star network cable will only take down one computer's network
access and not the entire LAN. (If the hub fails, however, the entire network also
fails.)

TREE TOPOLOGY

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Tree topologies integrate multiple star topologies together onto a bus. In its
simplest form, only hub devices connect directly to the tree bus, and each hub
functions as the "root" of a tree of devices. This bus/star hybrid approach supports
future expandability of the network much better than a bus (limited in the number
of devices due to the broadcast traffic it generates) or a star (limited by the number
of hub connection points) alone.

MESH TOPOLOGY

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FIG 5 MESH TOPOLOGY

Mesh topologies involve the concept of routes. Unlike each of the previous
topologies, messages sent on a mesh network can take any of several possible
paths from source to destination. (Recall that even in a ring, although two cable
paths exist, messages can only travel in one direction.) Some WANs, most notably
the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a
full mesh. As shown in the illustration below, partial mesh networks also exist in
which some devices connect only indirectly to others.

REFERENCE MODELS

OSI REFERENCEMODEL

 This model is based on the proposal developed by International standards
Organization
 It was revised in the in 1995.
 This model is called ISO OSI reference model.
 This OSI model has seven layers:

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Figure
1: OSI

reference model.

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OSI reference model.
They are
 Physical layer
 Data Link Layer
 Network Layer
 Transport Layer
 Session Layer
 Presentation Layer
 Application Layer

PHYSICAL LAYER

The physical layer is concerned with transmitting raw bits over a
communication channel.

The design issue here largely deals with mechanical , electrical , and
timing interfaces and the physical transmission medium which lies below the
physical layer.

The information can be transmitted on wires by varying some
physical property such as voltage or current.

Various transmission media such as magnetic media, twisted pair,
coaxial cable, fibre optics are used for actual transmission.

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Physical layer standards and protocols are concerned with
issues such as the following:
 How a physical circuit is established between communicating devices.
 How the circuit is terminated when no longer needed.
 The physical form (e.g., voltages, frequencies, and timing) in which
data bits (binary values 0 and 1) are represented.
 Whether transmission of data can take place in one or both directions
over the same physical connection.
 Characteristics of the physical media that carry the signals (e.g.,
copper wire, optical fiber, radio waves).
 Characteristics of the connectors used for connecting the physical
media.
 How data from a number of sources should be multiplexed before
transmission and demultiplexed upon arrival, and the type of
multiplexing technique to be used.
 The type of modulation to be used for transmitting digital data over
analog transmission lines.
The physical layer accounts for much of the tangible components of a
network, including cables, satellites, earth stations, repeaters, multiplexers,
concentrators, and modems. Physical layer protocols and standards are of
mechanical, electrical, functional, and procedural nature.
The physical layer hides the above details from the higher layers. To the data
link layer, it appears as a logical communication channel which can send a stream
of bits from one point in the network to another

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DATA LINK LAYER

The main task of the data link layer is to transform a raw transmission
facility into a line that appears free of undetected transmission errors to the
network layer.

Another issue in the data link layer is how to keep a fast transmitter
from drowning slow receiver in data.

The data link layer breaks the data into data frames, transmits the frames
sequentially over the channel, and checks for transmission errors by requiring the
receiving end to send back acknowledgment frames.

Data link protocols are concerned with the following issues:
 How to divide the data into frames.
 How to delimit frames by adding special bit patterns to the beginning
and end of each frame. This allows the receiving end to detect where
each frame begins and where it ends.
 Error detection. Some form of error check is included in the frame
header. This is constructed by the transmitting end based on the
contents of the frame, and checked for integrity by the receiving end.
A change in the frame bits can be detected in this way.
 Error correction. When a frame arrives corrupted or is for any reason
lost in the network, it is retransmitted. Lost acknowledgment frames

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may result in duplicate frames, which need to be detected and
corrected as well.
 Flow control. In general, not all communication devices in a network
operate at the same speed. Flow control provides a means of avoiding
a slow receiver from being swamped by data from a fast transmitter.
NETWORK LAYER

The network layer controls the operation of the subnet.
The key design issue is determining how packets are routed from source and
destination.

The network layer converts the data into packets and ensures that the packets
are delivered to their final destination, where they can be converted back into the
original data.
Network layer protocols are concerned with the following issues:
 The interface between a host and the network.
 The interface between two hosts across the network.
 Routing of packets across the network, including the allocation of
a route and handling of congestion.
 Correct ordering of packets to reflect the original order of data.
 Collection of statistical information (e.g., number of transmitted
packets) for performance measurement and accounting purposes.
 Internetworking: communication between two or more networks

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TRANSPORT LAYER

The basic function of the transport layer is to accept data from above layers,
split it up into smaller units if need be pass these to the network layer and ensure
that the pieces all arrive correctly at the other end.

The transport layer also determines what type of service to provide to the
session layer and ultimately to the users of the network.
Transport layer protocols are concerned with the following issues:
 Establishment and termination of host-to-host connections.
 Efficient and cost-effective delivery of data across the network from
one host to another.
 Multiplexing of data, if necessary, to improve use of network
bandwidth, and demultiplexing at the other end.
 Splitting of data across multiple network connections, if necessary, to
improve throughput, and recombining at the other end.
 Flow control between hosts.
 Addressing of messages to their corresponding connections. The
address information appears as a part of the message header.
 Type of service to be provided to the session layer (e.g., error-free
versus error-prone connections, whether messages should be delivered
in the order received or not).

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THE SESSION LAYER

The session layer allows users on different machines to establish sessions
between them.
Sessions offer various services including dialog control, token management
and synchronization.
Session layer protocols are concerned with the following issues:
 Negotiating the establishment of a connection (a session) between
user processes on communicating hosts, and its subsequent
termination. This includes the setting of various communication
parameters for the session (e.g., synchronization and control).
 Correct ordering of messages when this function is not performed by
the transport layer.
 Recovery from interrupted transport connections, if necessary.
 Grouping of messages into a larger message, if necessary, so that the
larger message becomes available at the destination only when its
constituent messages have all been delivered successfully.

PRESENTATION LAYER

Presentation layer is concerned with syntax and semantics of the information
transmitted

Presentation layer protocols are concerned with issues such as the following:

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 Abstract representation of application data.
 Binary representation of application data.
 Conversion between the binary representation of application data and
a common format for transmission between peer applications.
 Data compression to better utilize network bandwidth.
 Data encryption as a security measure.

APPLICATION LAYER

 The application layer contains a variety of protocols that are
commonly needed by users.
 One widely- used application protocol is HTTP which is the basis for
the World Wide Web.

 The application layer provides standards for supporting a variety of
application-independent services. Examples include:
 Virtual terminal standards to allow applications to communicate with
different types of terminals in a device-independent manner.
 Message handling system standards used for electronic mail.
 File transfer, access, and management standards for exchanging files
or parts there of between different systems.
 Transaction processing standards to allow different companies with
different systems to access each other’s on-line databases (e.g., in
banking and airline reservation).

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 On-line directory standards for storing details of individuals,
organizations, and network components.
 Standards for exchanging formatted documents.

The OSI Model of Computer Networks

 This diagram illustrates the Open Systems Interconnection (OSI) model. OSI
is primarily used today as a teaching tool.

 It conceptually devices a network into seven layers in a logical progression.

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 The lower layers deal with electrical signals, chunks of binary data, and
routing of these data across networks.

 Higher levels cover network requests and responses, representation of data,
and network protocols as seen from a user's point of view.

 The OSI model was originally conceived as a standard architecture for
building network systems and indeed, many popular network technologies
today reflect the layered design of OSI.

Benefits of the OSI Model

 By separating the network communications into logical smaller pieces, the
OSI model simplifies how network protocols are designed.

 The OSI model was designed to ensure different types of equipment (such as
network adapters, hubs, and routers) would all be compatible even if built by
different manufacturers. A product from one network equipment vendor that
implements OSI Layer 2 functionality, for example, will be much more
likely to interoperate with another vendor's OSI Layer 3 product because
both vendors are following the same model.

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 The OSI model also makes network designs more extensible as new
protocols and other network services are generally easier to add to a layered
architecture than to a monolithic one.

TCP/IP REFERENCE MODEL

INTRODUCTION

 TCP and IP were developed by a Department of Defense (DOD)
research project to connect a number different networks designed by
different vendors into a network of networks (the "Internet").

 It was initially successful because it delivered a few basic services
that everyone needs (file transfer, electronic mail, remote logon)
across a very large number of client and server systems.
 Several computers in a small department can use TCP/IP (along with
other protocols) on a single LAN.
 The IP component provides routing from the department to the
enterprise network, then to regional networks, and finally to the global
Internet.

Definition:

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 Transmission Control Protocol (TCP) and Internet Protocol (IP) are two
distinct network protocols, technically speaking. TCP and IP are so
commonly used together, however, that TCP/IP has become standard
terminology to refer to either or both of the protocols.

 IP corresponds to the Network layer (Layer 3) in the OSI model, whereas
TCP corresponds to the Transport layer (Layer 4) in OSI. In other words, the
term TCP/IP refers to network communications where the TCP transport is
used to deliver data across IP networks.

TCP/IP Networking Protocols

The TCP/IP suite of protocols is the set of protocols used to communicate across
the internet. It is also widely used on many organizational networks due to its
flexibility and wide array of functionality provided. Microsoft who had originally
developed their own set of protocols now is more widely using TCP/IP, at first for
transport and now to support other services.

TCP/IP by Layer

Link Layer

 SLIP - Serial Line Internet Protocol. This protocol places data packets into
data frames in preparation for transport across network hardware media.
This protocol is used for sending data across serial lines. There is no error
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correction, addressing or packet identification. There is no authentication or
negotiation capability with SLIP. SLIP will only support transport of IP
packets.

 CSLIP - Compressed SLIP is essentially data compression of the SLIP
protocol. It uses Van Jacobson compression to drastically reduce the
overhead of packet overhead. This may also be used with PPP and called
CPPP.

 PPP - Point to Point Protocol is a form of serial line data encapsulation that
is an improvement over SLIP which provides serial bi-directional
communication. It is much like SLIP but can support AppleTalk, IPX,
TCP/IP, and NetBEUI along with TCP/IP which is supported by SLIP. It can
negociate connection parameters such as speed along with the ability to
support PAP and CHAP user authentication.

 Ethernet - Ethernet is not really called a protocol. There are also many types
of Ethernet. The most common Ethernet which is used to control the
handling of data at the lowest layer of the network model is 802.3 Ethernet.
802.3 Ethernet privides a means of encapsulating data frames to be sent
between computers. It specifies how network data collisions are handled
along with hardware addressing of network cards.
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Network Layer

 ARP - Address Resolution Protocol enables the packaging of IP data into
ethernet packages. It is the system and messaging protocol that is used to
find the ethernet (hardware) address from a specific IP number. Without this
protocol, the ethernet package could not be generated from the IP package,
because the ethernet address could not be determined.

 IP - Internet Protocol. Except for ARP and RARP all protocols' data packets
will be packaged into an IP data packet. IP provides the mechanism to use
software to address and manage data packets being sent to computers.

 RARP - Reverse address resolution protocol is used to allow a computer
without a local permanent data storage media to determine its IP address
from its ethernet address.

Transport Layer

 TCP - A reliable connection oriented protocol used to control the
management of application level services between computers. It is used for
transport by some applications.

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 UDP - An unreliable connection less protocol used to control the
management of application level services between computers. It is used for
transport by some applications which must provide their own reliability.

 ICMP - Internet control message protocol (ICMP) provides management and
error reporting to help manage the process of sending data between
computers. (Management). This protocol is used to report connection status
back to computers that are trying to connect other computers. For example,
it may report that a destination host is not reachable.

 IGMP - Internet Group Management Protocol used to support multicasting.
IGMP messages are used by multicast routers to track group memberships
on each of its networks.

Application Layer

 FTP - File Transfer Protocol allows file transfer between two computers
with login required.

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 TFTP - Trivial File Transfer Protocol allows file transfer between two
computers with no login required. It is limited, and is intended for diskless
stations.

 NFS - Network File System is a protocol that allows UNIX and Linux
systems remotely mount each other's file systems.

 SNMP - Simple Network Management Protocol is used to manage all types
of network elements based on various data sent and received.

 SMTP - Simple Mail Transfer Protocol is used to transport mail. Simple
Mail Transport Protocol is used on the internet, it is not a transport layer
protocol but is an application layer protocol.

 HTTP - Hypertext Transfer Protocol is used to transport HTML pages from
web servers to web browsers. The protocol used to communicate between
web servers and web browser software clients.

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 BOOTP - Bootstrap protocol is used to assign an IP address to diskless
computers and tell it what server and file to load which will provide it with
an operating system.

 DHCP - Dynamic host configuration protocol is a method of assigning and
controlling the IP addresses of computers on a given network. It is a server
based service that automatically assigns IP numbers when a computer boots.
This way the IP address of a computer does not need to be assigned
manually. This makes changing networks easier to manage. DHCP can
perform all the functions of BOOTP.

 BGP - Border Gateway Protocol. When two systems are using BGP, they
establish a TCP connection, then send each other their BGP routing tables.
BGP uses distance vectoring. It detects failures by sending periodic keep
alive messages to its neighbors every 30 seconds. It exchanges information
about reachable networks with other BGP systems including the full path of
systems that are between them. Described by RFC 1267, 1268, and 1497.

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 EGP - Exterior Gateway Protocol is used between routers of different
systems.

 IGP - Interior Gateway Protocol. The name used to describe the fact that
each system on the internet can choose its own routing protocol. RIP and
OSPF are interior gateway protocols.

 RIP - Routing Information Protocol is used to dynamically update router
tables on WANs or the internet. A distance-vector algorithm is used to
calculate the best route for a packet. RFC 1058, 1388 (RIP2).

 OSPF - Open Shortest Path First dynamic routing protocol. A link state
protocol rather than a distance vector protocol. It tests the status of its link to
each of its neighbors and sends the acquired information to them.

 POP3 - Post Office Protocol version 3 is used by clients to access an internet
mail server to get mail. It is not a transport layer protocol.

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 IMAP4 - Internet Mail Access Protocol version 4 is the replacement for
POP3.

 Telnet is used to remotely open a session on another computer. It relies on
TCP for transport and is defined by RFC854.

Bandwidth Control

 BAP - Bandwidth Allocation Protocol is a bandwidth control protocol for
PPP connections. It works with BACP.


 BACP - Bandwidth Allocation Control Protocol.

TCP/IP by Function

Packaging and Low Level

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 SLIP - Serial Line Internet Protocol. This protocol places data packets into
data frames in preparation for transport across network hardware media.
This protocol is used for sending data across serial lines. There is no error
correction, addressing or packet identification. There is no authentication or
negotiation capabilities with SLIP. SLIP will only support transport of IP
packets.

 Ethernet - Ethernet is not really called a protocol. There are also many types
of ethernet. The most common ethernet which is used to control the handling
of data at the lowest layer of the network model is 802.3 ethernet. 802.3
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ethernet privides a means of encapsulating data frames to be sent between
computers. It specifies how network data collisions are handled along with
hardware addressing of network cards.

Transport and Basic Functions

 TCP - A reliable connection oriented protocol used to control the
management of application level services between computers. It is used for
transport by some applications.

 UDP - An unreliable connection less protocol used to control the
management of application level services between computers. It is used for
transport by some applications which must provide their own reliability.

Network Management

 SNMP - Simple Network Management Protocol is used to manage all types
of network elements based on various data sent and received.

 ICMP - Internet control message protocol provides management and error
reporting to help manage the process of sending data between computers.
(Management). This protocol is used to report connection status back to
computers that are trying to connect other computers. For example, it may
report that a destination host is not reachable. This protocol is required for
basic TCP/IP operations.
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 ARP - Address Resolution Protocol enables the packaging of IP data into
ethernet packages. It is the system and messaging protocol that is used to
find the ethernet (hardware) address from a specific IP number. Without this
protocol, the ethernet package could not be generated from the IP package,
because the ethernet address could not be determined. protocol is used to
report connection status back to computers that are trying to connect other
computers. For example, it may report that a destination host is not
reachable. This protocol is required for basic TCP/IP operations.

Host Management

 BOOTP - Bootstrap protocol is used to assign an IP address to diskless
computers and tell it what server and file to load which will provide it with
an operating system.

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 RARP - Reverse address resolution protocol is used to allow a computer
without a local permanent data storage media to determine its IP address
from its ethernet address.

Mail Protocols

 SMTP - Simple Mail Transfer Protocol is used to transport mail. Simple
Mail Transport Protocol is used on the internet, it is not a transport layer
protocol but is an application layer protocol.

 POP3 - Post Office Protocol version 3 is used by clients to access an internet
mail server to get mail. It is not a transport layer protocol.

 IMAP4 - Internet Mail Access Protocol version 4 is the replacement for
POP3.

Multicasting Protocols

 IGMP - Internet Group Management Protocol used to support multicasting.
IGMP messages are used by multicast routers to track group memberships
on each of its networks.

Routing Protocols

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 BGP - Border Gateway Protocol. When two systems are using BGP, they
establish a TCP connection, then send each other their BGP routing tables.

 BGP uses distance vectoring. It detects failures by sending periodic keep
alive messages to its neighbors every 30 seconds. It exchanges information
about reachable networks with other BGP systems including the full path of
systems that are between them. Described by RFC 1267, 1268, and 1497

 EGP - Exterior Gateway Protocol is used between routers of different
systems.

 IGP - Interior Gateway Protocol. The name used to describe the fact that
each system on the internet can choose its own routing protocol. RIP and
OSPF are interior gateway protocols.

 RIP - Routing Information Protocol is used to dynamically update router
tables on WANs or the internet.

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 OSPF - Open Shortest Path First dynamic routing protocol. A link state
protocol rather than a distance vector protocol. It tests the status of its link to
each of its neighbors and sends the acquired information to them.

Networking protocols

A protocol is, simply put, a set of rules for communication.

Linux supports many different networking protocols. We list only the most
important:

TCP/IP

 The Transport Control Protocol and the Internet Protocol are the two most
popular ways of communicating on the Internet. A lot of applications, such
as your browser and E-mail program, are built on top of this protocol suite.

 Very simply put, IP provides a solution for sending packets of information
from one machine to another, while TCP ensures that the packets are

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arranged in streams, so that packets from different applications don't get
mixed up, and that the packets are sent and received in the correct order.

 The Internet was originally developed three decades ago for the United
States Department of Defense (DoD), mainly for the purpose of
interconnecting different-brand computers. Another reason for the
development of TCP/IP was to provide a reliable data transport system over
an unreliable network.

 TCP/IP networking has been present in Linux since its beginnings. It has
been implemented from scratch. It is one of the most robust, fast and reliable
implementations and is one of the key factors of the success of Linux. Linux
and networking are made for each other, in so much that not connecting your
Linux system to the network may result in slow startup and other troubles.
Even if you don't use any network connections to other computers,
networking protocols are used for internal system and application
communications. Linux expects to be networked.

A good starting point for learning more about TCP and IP is in the following
documents:

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 Man 7 ip : Describes the IPv4 protocol implementation on Linux (version 4
currently being the most wide-spread edition of the IP protocol).
 Man 7 tcp : Implementation of the TCP protocol.
 RFC793, RFC1122, RFC2001 for TCP, and RFC791, RFC1122 and
RFC1112 for IP.

The Request for Comments documents contains the descriptions of
networking standards, protocols, applications and implementation. These
documents are managed by the Internet Engineering Task Force, an
international community concerned with the smooth operation of the Internet
and the evolution and development of the Internet architecture.

Your ISP usually has an RFC archive available, or you can browse the RFCs

TCP/IPv6

 Nobody expected the Internet to grow as fast as it does. IP proved to have
quite some disadvantages when a really large number of computers is in a
network, the most important being the availability of unique addresses to
assign to each machine participating. Thus, IP version 6 was devices to meet
the needs of today's Internet.

 Unfortunately, not all applications and services support IPv6, yet. A
migration is currently being set in motion in many environments that can
benefit from an upgrade to IPv6. For some applications, the old protocol is

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still used, for applications that have been reworked the new version is
already active. So when checking your network configuration, sometimes it
might be a bit confusing since all kinds of measures can be taken to hide one
protocol from the other so as the two don't mix up connections.

More information can be found in the following documents:

 Man 7 ipv6 : the Linux IPv6 protocol implementation.
 RFC1883 describing the IPv6 protocol.

PPP, SLIP, PLIP, PPPOE

 The Linux kernel has built-in support for PPP (Point-to-Point-Protocol),
SLIP (Serial Line IP) and PLIP (Parallel Line IP). PPP is the most popular
way individual users access their ISP (Internet Service Provider), although in
densely populated areas it is often being replaced by PPPOE, PPP over
Ethernet, the protocol used in cable modem connections.

 Most Linux distributions provide easy-to-use tools for setting up an Internet
connection. The only thing you basically need is a username and password
to connect to your Internet Service Provider (ISP), and a telephone number
in the case of PPP.

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Definition:

 A network protocol defines rules and conventions for communication
between network devices. Protocols for computer networking all generally
use packet switching techniques to send and receive messages in the form of
packets.

 Network protocols include mechanisms for devices to identify and make
connections with each other, as well as formatting rules that specify how
data is packaged into messages sent and received. Some protocols also
support message acknowledgement and data compression designed for
reliable and/or high-performance network communication. Hundreds of
different computer network protocols have been developed each designed
for specific purposes and environments.

Internet Protocols

 The Internet Protocol family contains a set of related (and among the most
widely used network protocols. Besides Internet Protocol (IP) itself, higher-
level protocols like TCP, UDP, HTTP, and FTP all integrate with IP to
provide additional capabilities. Similarly, lower-level Internet Protocols like
ARP and ICMP also co-exist with IP. These higher level protocols interact
more closely with applications like Web browsers while lower-level
protocols interact with network adapters and other computer hardware.

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Routing Protocols

Routing protocols are special-purpose protocols designed specifically for use by
network routers on the Internet. Common routing protocols include EIGRP, OSPF
and BGP.

How Network Protocols Are Implemented

 Modern operating systems like Microsoft Windows contain built-in services
or daemons that implement support for some network protocols.

 Applications like Web browsers contain software libraries that support the
high level protocols necessary for that application to function. For some
lower level TCP/IP and routing protocols, support is implemented in directly
hardware (silicon chipsets) for improved performance.

Access 3000 X.25 - TCP/IP Gateway with ISDN

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Overview

 X.25 to TCP/IP Conversion Gateway
 TCP/IP to X.25 Conversion Gateway
 X.25 over TCP (XOT) Encapsulation Gateway

The Access 3000 Gateway offers comprehensive solutions to a migration from
X.25 networking to TCP/IP networking. The product supports both X.25 to TCP
conversion and X.25 over TCP encapsulation.

X.25 to TCP conversion enables X.25 devices to interface with TCP/IP devices.
The Gateway terminates each protocol stack and interconnects sessions between
them. This interconnection may be as simple as data-only transfer, or more
complex like ―message boundary preservation‖ for X.25 M-bit packet sequences,
and message conversion for packets like interrupt and Q-bit data. These latter
methods require modest modification to the TCP/IP application.

Using X.25 to TCP conversion multiple X.25 devices can be concentrated in a
single Gateway. Multiple gateway sessions are supported across a distributed
network, using both X.25 PVCs and SVCs.

An alternate approach is to use encapsulation to transport X.25 over TCP via XOT
over IP (RFC 1613). By tunneling the X.25 packet layer over TCP, the Gateway
allows for seamless integration without modification or re-configuration of the

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X.25 devices. All network addressing is preserved. By transporting the packets, the
gateway preserves all of the options of the X.25 protocol.

An X.25-TCP Gateway is required at each site where X.25 devices are located.
Multiple X.25 ports on the Gateway allow multiple devices to be concentrated.

Key Software Features

 X.25 to TCP/IP Gateway using:
 X.25 to TCP conversion
 X.25 over TCP (XOT) encapsulation (RFC 1613)
 SVC and PVC connections supported
 Serial to TCP/IP support for terminal server applications
 Remote management via Telnet and SNMP over IP
 Interface tracing

Key Hardware Features

 V.24/V.35 DB-25 WAN port
 RS-232 RJ-45 sync/ async serial port
 RS-232 RJ-45 console port
 10-BaseT Ethernet port
 Optional NEBS Certification

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Access 3000 X.25 - TCP/IP Gateway

Overview

 X.25 to TCP/IP Conversion Gateway
 TCP/IP to X.25 Conversion Gateway
 X.25 over TCP (XOT) Encapsulation Gateway

The Access 3000 Gateway offers comprehensive solutions to a migration from
X.25 networking to TCP/IP networking. The product supports both X.25 to TCP
conversion and X.25 over TCP encapsulation.

Using X.25 to TCP conversion multiple X.25 devices can be concentrated in a
single Gateway. Multiple gateway sessions are supported across a distributed
network, using both X.25 PVCs and SVCs.

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An alternate approach is to use encapsulation to transport X.25 over TCP via XOT
over IP (RFC 1613). By tunnelling the X.25 packet layer over TCP, the Gateway
allows for seamless integration without modification or re-configuration of the
X.25 devices. All network addressing is preserved. By transporting the packets, the
gateway preserves all of the options of the X.25 protocol.

An X.25-TCP Gateway is required at each site where X.25 devices are located.
Multiple X.25 ports on the Gateway allow multiple devices to be concentrated.

Key Software Features

Key Hardware Features

 V.24/V.35 DB-25 WAN port
 RS-232 RJ-45 sync/async serial port
 RS-232 RJ-45 console port
 10-BaseT Ethernet port
 NEBS approved (optional)

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TCP/IP LAYER

THE INTERNET LAYER
 The internet layer allows the hosts to inject the packets into any
network and have them travel independently to the destination.

 The packets may change in order they were sent. It is the duty to
higher layers to rearrange the packets.

 The internet layer defines the official packet format and protocol
called Internet protocol.

 The job of this layer is to deliver IP packets where they are supposed
to go.

 Packet routing is for avoiding congestion. The TCP/IP internet layer
is similar in functionality to the OSI network layer.
The internet protocol is performs two basic functions
 Host Addressing and identification- It is accomplished with a
hierarchical addressing system.

 Packet routing-This is the basic task of getting packets of data
(datagram’s) from source to destination by sending them to the next
network node (router) closer to the final destination.

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 The IP can carry data for a number of different upper layer protocols
such as Internet Control Message Protocol (ICMP), Internet Group
Management Protocol (IGMP).

TRANSPORT LAYER

 The layer above the internet layer is transport layer.
 This layer allows peer entities on the source and destination hosts to carry on
a conversation.
 There are two end-end transport protocols in the transport layer. They are
TCP (Transmission control protocol) and UDP (User Datagram Protocol).

 The first protocol is TCP which is connection oriented protocol allows byte
stream originating from the source machine to be delivered without error to
other destination machine in the internet.

 It fragments the incoming byte stream into discrete messages and sent to the
internet layer.
 The TCP process in the destination reassembles the incoming message into
output stream.

 The second protocol is UDP is unreliable , connectionless protocol is applied
for the applications that do not want TCP’s sequencing and or flow and wish
to provide their own.

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APPLICATION LAYER
 On the top of the transport layer is application layer.
 It contains all the higher level protocols. It includes virtual terminal
(TELNET), file transfer (FTP) and electronic mail (SMTP).
 The virtual terminal protocol allows the user on one machine to log onto a
distant machine and work there.

 The file transfer protocol provides a way to move data efficiently from one
machine to another.

 Electronic mail was originally just a kind of file transfer, but later a
specialized protocol was developed for it.

Host-to-network layer

Below the internet is a great void. The TCP/IP does not really say much
about what happens here, except to point out that the host has to connect to the
network using some protocol so it can send IP packets to it..

DIFFERENCE BETWEEN OSI REFERENCE MODEL AND TCP/IP MODEL:
SLNO OSI REFERENCE MODEL TCP/IP MODEL
1 Service, interface and protocol are not Service, interface and protocol

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clearly defined. are clearly defined.
2 As the model is invented before the The protocols have been invented
protocols, functionalities on each layer before models, so the
is not optimized. functionalities are perfectly
described.
3 Contains seven layers Contains four layers
4 Both connectionless and connection Only one mode in network layer
oriented communication are supported (connectionless) but both modes
in the network layer. But only in the transport layer are
connection – oriented communication supported giving the users a
in the transport layer. choice.

Definition:

 UDP (User Datagram Protocol) is a simple OSI transport layer protocol for
client/server network applications based on Internet Protocol (IP). UDP is
the main alternative to TCP and one of the oldest network protocols in
existence, introduced in 1980.


 UDP is often used in videoconferencing applications or computer games
specially tuned for real-time performance. To achieve higher performance,
the protocol allows individual packets to be dropped (with no retries) and

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UDP packets to be received in a different order than they were sent as
dictated by the application.

UDP Datagram’s

UDP network traffic is organized in the form of datagram. A datagram comprises
one message unit. The first eight (8) bytes of a datagram contain header
information and the remaining bytes contain message data.

A UDP datagram header consists of four (4) fields of two bytes each:

 source port number
 destination port number
 datagram size
 checksum

UDP port numbers allow different applications to maintain their own channels for
data similar to TCP. UDP port headers are two bytes long; therefore, valid UDP
port numbers range from 0 to 65535.

The UDP datagram size is a count of the total number of bytes contained in header
and data sections. As the header length is a fixed size, this field effectively tracks
the length of the variable-sized data portion (sometimes called payload). The size
of datagram varies depending on the operating environment but has a maximum of
65535 bytes.

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UDP checksums protect message data from tampering. The checksum value
represents an encoding of the datagram data calculated first by the sender and later
by the receiver. Should an individual datagram be tampered with or get corrupted
during transmission, the UDP protocol detects a checksum calculation mismatch.
In UDP, check summing is optional as opposed to TCP where checksums are
mandatory.

USER DATAGRAM PROTOCOL

 The internet protocol suite supports a connectionless transport protocol,
UDP (User Datagram Protocol).

 UDP provides a way for applications to send encapsulated IP datagram and
send them without having to establish a connection.

Source port Destination port

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UDP length UDP checksum

Figure 2. the UDP header

 UDP transmits the segments consisting of a 8 byte header followed by the
payload.

 The two ports serve to identify the endpoints within the source and
destination machines.

 When a UDP packet arrives, its payload is handled to the process attached to
the destination port.

 This attachment occurs when BIND primitive or something similar is used.

 The main value of having UDP over just using raw IP is the addition of the
source and destination ports.

 Without the port fields, the transport layer would not know what to do with
the packet. With then it delivers the segment correctly.

 The source port is primarily needed when reply must be sent back to the
source.

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 By copying the source port field from the incoming segment into the
destination port field of the outgoing segment, the process sending the reply
can specify which process on the sending machine is to get it.

 The UDP length field includes the 8 byte header and the data.
 The UDP checksum is optional and stored as 0 if not computed

Disadvantages

It does not do flow control, error control and retransmission upon the receipt
of a bad segment. All of that is up to the user processes. It only provides interface
to the IP protocol.

Usage

One area where UDP is especially useful is in client-server situations.
Often, the client sends a short request to the server and expects a short reply back.
If either a request or reply is first, the client can just the time out and try again. An
application that uses UDP this way is DNS.

NETWORKING COMPONENTS

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NETWORK INTERFACE CARDS

A network card, network adapter, or NIC (network interface card) is a piece
of computer hardware designed to allow computers to communicate over a
computer network. It provides physical access to a networking medium and often
provides a low-level addressing system through the use of MAC addresses.

REPEATER

A repeater is an electronic device that receives a signal and retransmits it at a
higher level and/or higher power, or onto the other side of an obstruction, so that
the signal can cover longer distances.

The term "repeater" originated with telegraphy and referred to an
electromechanical device used to regenerate telegraph signals. Use of the term has
continued in telephony and data communications.

In telecommunication, the term repeater has the following standardized
meanings:

1. An analog device that amplifies an input signal regardless of its nature
(analog or digital).
2. A digital device that amplifies, reshapes, retimes, or performs a combination
of any of these functions on a digital input signal for retransmission.

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Because repeaters work with the actual physical signal, and do not
attempt to interpret the data being transmitted, they operate on the Physical
layer, the first layer of the OSI model.

USES

Repeaters are often used in trans-continental and submarine communications
cables, because the attenuation (signal loss) over such distances would be
unacceptable without them. Repeaters are used in both copper-wire cables carrying
electrical signals, and in fiber optics carrying light.

Repeaters are also used extensively in broadcasting, where they are known
as translators, boosters or TV relay transmitters.

In optical communications the term repeater is used to describe a piece of
equipment that receives an optical signal, converts that signal into an electrical
one, regenerates it, and then retransmits an optical signal. Since such a device
converts the optical signal into an electrical one, and then back to an optical signal,
they are often known as Optical-Electrical-Optical (OEO) repeaters.

BRIDGES

 Bridges tend to be more complex than hubs or repeaters. Bridges can
analyze incoming data packets to determine if the bridge is able to
send the given packet to another segment of the network.

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 Since bridging takes place at the data link layer of the OSI model, a
bridge processes the information from each frame of data it receives.
In an Ethernet frame, this provides the MAC address of the frame's
source and destination. Bridges use two methods to resolve the
network segment that a MAC address belongs to.

Transparent bridging — this method uses a forwarding database to send
frames across network segments. The forwarding database is initially empty and
entries in the database are built as the bridge receives frames. If an address
entry is not found in the forwarding database, the frame is rebroadcast to all
ports of the bridge, forwarding the frame to all segments except the source
address. By means of these broadcast frames, the destination network will
respond and a route will be created. Along with recording the network segment
to which a particular frame is to be sent, bridges may also record a bandwidth
metric to avoid looping when multiple paths are available. Devices that have
this transparent bridging functionality are also known as adaptive bridges. They
are primarily found in Ethernet networks.

Source route bridging — with source route bridging two frame types are
used in order to find the route to the destination network segment. Single-Route
(SR) frames make up most of the network traffic and have set destinations, while
All-Route (AR) frames are used to find routes. Bridges send AR frames by
broadcasting on all network branches; each step of the followed route is registered
by the bridge performing it. Each frame has a maximum hop count, which is
determined to be greater than the diameter of the network graph, and is
decremented by each bridge.

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Frames are dropped when this hop count reaches zero, to avoid indefinite
looping of AR frames. The first AR frame which reaches its destination is
considered to have followed the best route, and the route can be used for
subsequent SR frames; the other AR frames are discarded. This method of locating
a destination network can allow for indirect load balancing among multiple bridges
connecting two networks. The more a bridge is loaded, the less likely it is to take
part in the route finding process for a new destination as it will be slow to forward
packets.

A new AR packet will find a different route over a less busy path if one
exists. This method is very different from transparent bridge usage, where
redundant bridges will be inactivated; however, more overhead is introduced to
find routes, and space is wasted to store them in frames. A switch with a faster
backplane can be just as good for performance, if not for fault tolerance. They are
primarily found in Token Ring networks.

Bridges come in three basic types

1. Local bridges: Directly connect local area networks (LANs)
2. Remote bridges: Can be used to create a wide area network (WAN) link
between LANs. Remote bridges, where the connecting link is slower than
the end networks, largely have been replaced with routers.
3. Wireless bridges: Can be used to join LANs or connect remote stations to
LANs

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Advantages of network bridges

 Self-configuring
 Primitive bridges are often inexpensive
 Reduce the size of collision domain by micro segmentation in non-switched
networks
 Transparent to protocols above the MAC layer
 Allows the introduction of management/performance information and access
control
 LANs interconnected are separate, and physical constraints such as number
of stations, repeaters and segment length don't apply
 Helps minimize bandwidth usage
 used to interconnect two LANs

Disadvantages of network bridges

 Does not limit the scope of broadcasts
 Does not scale to extremely large networks
 Buffering introduces store and forward delays; on average traffic destined
for bridge will be related to the number of stations on the rest of the LAN
 Bridging of different MAC protocols introduces errors
 Because bridges do more than repeaters by viewing MAC addresses, the
extra processing makes them slower than repeaters
 Bridges are more expensive than repeaters

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Bridging versus routing

Bridging and routing are both ways of performing data control, but work
through different methods.

Bridging takes place at OSI Model Layer 2 (data-link layer) while routing
takes place at the OSI Model Layer 3 (network layer).

This difference means that a bridge directs frames according to hardware
assigned MAC addresses while a router makes its decisions according to arbitrarily
assigned IP Addresses.

As a result of this, bridges are not concerned with and are unable to
distinguish networks while routers can.

When designing a network, one can choose to put multiple segments into
one bridged network or to divide it into different networks interconnected by
routers.

If a host is physically moved from one network area to another in a routed
network, it has to get a new IP address; if this system is moved within a bridged
network, it doesn't have to reconfigure anything. These days bridges are replaced
with switches.

HUB

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A network hub is a fairly unsophisticated broadcast device. Hubs do not
manage any of the traffic that comes through them, and any packet entering any
port is broadcast out on all other ports.

Hubs classify as Layer 1 devices in the OSI model. At the physical layer,
hubs can support little in the way of sophisticated networking. Hubs do not read
any of the data passing through them and are not aware of their source or
destination. Essentially, a hub simply receives incoming packets, possibly
amplifies the electrical signal, and broadcasts these packets out to all devices on
the network - including the one that originally sent the packet.

There three different types of hubs exist:

1. Passive (A hub which does not need an external power source, because it does
not regenerate the signal and therefore falls as part of the cable, with respect to
maximum cable lengths)

2. Active (A hub which regenerates the signal and therefore needs an external
power supply)

3. Intelligent (A hub which provides error detection (e.g. excessive collisions) and
also does what an active hub does)

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Passive hubs do not amplify the electrical signal of incoming packets before
broadcasting them out to the network. Active hubs, on the other hand, do perform
this amplification, as does a different type of dedicated network device called a
repeater. Another, not so common, name for the term concentrator is referring to a
passive hub and the term multi port repeater is referred to an active hub.

Intelligent hubs add extra features to an active hub that are of particular
importance to businesses. An intelligent hub typically is stackable (built in such a
way that multiple units can be placed one on top of the other to conserve space). It
also typically includes remote management capabilities via Simple Network
Management Protocol (SNMP) and virtual LAN (VLAN) support.

USES

For inserting a protocol analyzer into a network connection, a hub is an
alternative to a network tap or port mirroring.

When a switch is accessible for end users to make connections, for example,
in a conference room, an inexperienced or careless user (or saboteur) can bring
down the network by connecting two ports together, causing a loop. This can be
prevented by using a hub, where a loop will break other users on the hub, but not
the rest of the network. (It can also be prevented by buying switches that can detect
and deal with loops, for example by implementing the Spanning Tree Protocol.)

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A hub with a 10BASE2 port can be used to connect devices that only
support 10BASE2 to a modern network. The same goes for linking in an old
thicknet network segment using an AUI port on a hub (individual devices that were
intended for thicknet can be linked to modern Ethernet by using an AUI-10BASE-
T transceiver).

Switches

A network switch is a device that forwards and filters OSI layer 2 data
grams (chunk of data communication) between ports (connected
cables) based on the MAC addresses in the packets.

 This is distinct from a hub in that it only forwards the packets to the
ports involved in the communications rather than all ports connected.

 Strictly speaking, a switch is not capable of routing traffic based on IP
address (OSI Layer 3) which is necessary for communicating between
network segments or within a large or complex LAN.

 Some switches are capable of routing based on IP addresses but are
still called switches as a marketing term.

 A switch normally has numerous ports, with the intention being that
most or all of the network is connected directly to the switch, or
another switch that is in turn connected to a switch.

 Switch is a marketing term that encompasses routers and bridges, as
well as devices that may distribute traffic on load or by application
content (e.g., a Web URL identifier). Switches may operate at one or

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more OSI model layers, including physical, data link, network, or
transport (i.e., end-to-end).

 A device that operates simultaneously at more than one of these layers
is called a multilayer switch.

 Many experienced network designers and operators recommend
starting with the logic of devices dealing with only one protocol level,
not all of which are covered by OSI.

 Multilayer device selection is an advanced topic that may lead to
selecting particular implementations, but multilayer switching is
simply not a real-world design concept.

Routers

A router is a networking device that forwards packets between networks
using information in protocol headers and forwarding tables to determine the best
next router for each packet. Routers work at the Network Layer of the OSI model
and the Internet Layer of TCP/IP.

INTERNETWORK

An Internet work is the connection of two or more distinct computer
networks or network segments via a common routing technology. The result is
called an internet work.

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In modern practice, interconnected networks use the Internet Protocol. There
are at least three variants of internet works, depending on who administers and
who participates in them:

Intranet
Extranet
Internet

Intranets and extranets may or may not have connections to the Internet. If
connected to the Internet, the intranet or extranet is normally protected from being
accessed from the Internet without proper authorization. The Internet is not
considered to be a part of the intranet or extranet, although it may serve as a portal
for access to portions of an extranet.

INTRANET

An intranet is a set of networks, using the Internet Protocol and IP-based
tools such as web browsers and file transfer applications, which are under the
control of a single administrative entity.

That administrative entity closes the intranet to all but specific, authorized
users.

Most commonly, an intranet is the internal network of an organization.

A large intranet will typically have at least one web server to provide users
with organizational information.

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EXTRANET

An extranet is a network or internet work that is limited in scope to a single
organization or entity but which also has limited connections to the networks of
one or more other usually, but not necessarily, trusted organizations or entities

INTERNET

The Internet consists of a worldwide interconnection of governmental,
academic, public, and private networks based upon the networking technologies of
the Internet Protocol Suite.

It is the successor of the Advanced Research Projects Agency Network
(ARPANET) developed by DARPA of the U.S. Department of Defense. The
Internet is also the communications backbone underlying the World Wide Web
(WWW).

The 'Internet' is most commonly spelled with a capital 'I' as a proper noun,
for historical reasons and to distinguish it from other generic internet works.

Participants in the Internet use a diverse array of methods of several hundred
documented, and often standardized, protocols compatible with the Internet
Protocol Suite and an addressing system (IP Addresses) administered by the
Internet Assigned Numbers Authority and address registries.
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Service providers and large enterprises exchange information about the
reachability of their address spaces through the Border Gateway Protocol (BGP),
forming a redundant worldwide mesh of transmission paths.

BASIC PRINCIPLES OF NETWORKS

COMPUTER NETWORK

A computer network is a group of interconnected computers. A computer
network allows computers to communicate with many other and to share resources
and information.

TYPES OF NETWORKS
Based on the scale the networks are divided into several types. They aye
Large Area Network, Wide Area Network, Metropolitan Area Network etc..,

LARGE AREA NETWORK

Local Area Network, generally called LAN’s are privately-owned networks
within a single building or campus of up to a few kilometers in size.

WIDE AREA NETWORK
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A Wide Area Network, or WAN, spans a large geographical area often a
country or continent.
It contains a collection of machines intended for running user programs.

METROPOLITAN AREA NETWORK

A Metropolitan Area Network (man) is a network that connects two or more
local area networks or campus area networks together but does not extend beyond
the boundaries of the immediate town/city. Routers, switches and hubs are
connected to create a metropolitan area network.

PERSONAL AREA NETWORK

A personal area network (PAN) is a computer network used for
communication among computer devices close to one person.

VIRTUAL PRIVATE NETWORK

A virtual private network (VPN) is a computer network in which some of the
links between nodes are carried by open connections or virtual circuits in some
larger network (e.g., the Internet) instead of by physical wires.

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REFERENCE MODELS

OSI REFENCE MODEL

PHYSICAL LAYER

The Physical layer provides the electrical and mechanical interface to the
network medium (the cable). This layer gives the data-link layer (layer 2) its ability
to transport a stream of serial data bits between two communicating systems; it
conveys the bits that move along the cable. It is responsible for making sure that
the raw bits get from one place to another, no matter what shape they are in, and
deals with the mechanical and electrical characteristics of the cable.

DATA LINK LAYER
The Data-Link layer handles the physical transfer, framing (the assembly of
data into a single unit or block), flow control and error-control functions (and
retransmission in the event of an error) over a single transmission link; it is

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responsible for getting the data packaged and onto the network cable. The data link
layer provides the network layer (layer 3) reliable information-transfer capabilities.

NETWORK LAYER
The Network layer establishes, maintains, and terminates logical and/or
physical connections. The network layer is responsible for translating logical
addresses, or names, into physical addresses.

TRANSPORT LAYER

The Transport layer ensures data is successfully sent and received between
the two computers.
If data is sent incorrectly, this layer has the responsibility to ask for
retransmission of the data.
This layer acts as an interface between the bottom and top three layers.

SESSION LAYER

The Session layer decides when to turn communication on and off between
two computers—it provides the mechanisms that control the data-exchange process
and coordinates the interaction between them.
It sets up and clears communication channels between two communicating
components.

PRESENTATION LAYER

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The Presentation layer performs code conversion and data reformatting
(syntax translation). It is the translator of the network, making sure the data is in
the correct form for the receiving application.

APPLICATION LAYER

The Application layer provides the user interface between the software
running in the computer and the network. It provides functions to the user’s
software, including file transfer access and management (FTAM) and electronic
mail.

TCP/IP REFERENCE MODEL

INTRODUCTION

TCP and IP were developed by a Department of Defense (DOD) research
project to connect a number different networks designed by different vendors into
a network of networks (the "Internet").

It was initially successful because it delivered a few basic services that
everyone needs (file transfer, electronic mail, remote logon) across a very large
number of client and server systems.
Several computers in a small department can use TCP/IP (along with other
protocols) on a single LAN.

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The IP component provides routing from the department to the enterprise
network, then to regional networks, and finally to the global Internet.

THE INTERNET LAYER
The internet layer allows the hosts to inject the packets into any network and
have them travel independently to the destination.

TRANSPORT LAYER

This layer allows peer entities on the source and destination hosts to carry on
a conversation.

APPLICATION LAYER
On the top of the transport layer is application layer. It contains all the higher
level protocols. It includes virtual terminal (TELNET),file transfer(FTP) and
electronic mail(SMTP).

Host-to-network layer

Below the internet is a great void. The TCP/IP does not really say much about
what happens here, except to point out that the host has to connect to the network
using some protocol so it can send IP packets to it..

USER DATAGRAM PROTOCOL

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The internet protocol suite supports a connectionless transport protocol,
UDP (User Datagram Protocol).

UDP provides a way for applications to send encapsulated IP datagram and
send them without having to establish a connection.

REPEATER

USES

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BRIDGES

Bridges tend to be more complex than hubs or repeaters. Bridges can
analyze incoming data packets to determine if the bridge is able to send the given
packet to another segment of the network.

Advantages of network bridges

 Self-configuring
 Primitive bridges are often inexpensive
 Reduce the size of collision domain by micro segmentation in non-switched
networks
 Helps minimize bandwidth usage
 used to interconnect two LANs

Disadvantages of network bridges

 Does not limit the scope of broadcasts
 Does not scale to extremely large networks
 Bridges are more expensive than repeaters
Definition:

 Routers are physical devices that join multiple wired or wireless networks
together. Technically, a wired or wireless router is a Layer 3 gateway,
meaning that the wired/wireless router connects networks (as gateways do),
and that the router operates at the network layer of the OSI model.

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Home net workers often use an Internet Protocol (IP) wired or wireless router, IP
being the most common OSI network layer protocol. An IP router

such as a DSL or cable modem broadband router joins the home's local area
network (LAN) to the wide-area network (WAN) of the Internet.

By maintaining configuration information in a piece of storage called the routing
table, wired or wireless routers also have the ability to filter traffic, either incoming
or outgoing, based on the IP addresses of senders and receivers. Some routers
allow the home net worker to update the routing table from a Web browser
interface. Broadband routers combine the functions of a router with those of a
network switch and a firewall in a single unit.

IP ADDRESS

Each Ethernet board worldwide has a unique Ethernet-address, it is a 48 bit numbe
(the first 24 bits indicate the manufacturer, the last 24 bits are a unique number for
each Ethernet board/controller-chip assigned by the manufacturer).

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This is also called the MAC-address.

When systems on a local area network ("LAN") are configured with NetBEUI or
IPX/SPX protocol, they use these hardware-addresses to identify each other, so
there is no need to define manually a network address.
But TCP/IP was designed as a Wide-area-network ("WAN"), able to continue to
function, even if part of the network was not operating ( damaged or destroyed).

TCP/IP uses IP-addresses, which are 32-bit numbers. To make it easier to
memorize such IP-addresses, they are usually expressed as 4 8-bit numbers
(example: 192.168.10.1), where each of the 4 numbers is within the range of '0' to
'255' (there are restriction on using '0' and '255', avoid using them.).
When setting up a small private network, you are free to use ANY IP-address,
however, when you are connected to a company network, you need to ask the
Network-administrator to assign you an IP-address. And if you are connected to
the Internet, your ISP (Internet Service Provider) will assign an IP-address to you.
Even if a network is NOT connected to the Internet, it has become custom to use
on private networks a range of IP-addresses, which are reserved for private
networks (that makes it later possible to connect your private network to the
Internet without having to re-configure everything). The reserved IP-address is:
192.168.x.y, where x=same number on all systems and y=different/unique number
on all systems.

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A small network of 3 systems would use:

You configure this IP-address in the properties of the TCP/IP-protocol:

(For now, simply enter as 'Subnet Mask" 255.255.255.0, it will be explained later
in this document)
That's it, if you just like to connect systems on a small network, the network should

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work and you can test the Connection using the TCP/IP ping.

On a small network, you can still memorize the IP-addresses used, but if your
network grows to 50+ systems, it becomes a serious management job. But TCP/IP
offers some help by allowing to configure it to:
"obtain an IP address AUTOMATICALLY":

To be able to make this automatic assignment, there needs to be now on the
network a database, keeping track of possible IP-addresses and to whom these
addresses have been assigned:
DHCP (Dynamic Host Configuration Protocol)
On bootup, the system sends out a call on the network to find a DHCP-server,
which assigns an IP-address to such a system. The IP-addresses are usually
assigned NOT permanently, but for a specific time (could be days, weeks, months
or on Internet-connections just for the ONE connection). If the system contacts the

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DHCP-server again during this time, the 'lease' on the IP-address is extended. But
if you come back from a long vacation, your 'lease' of the IP-address may have
expired, that IP-address may have been assigned now to somebody else, and
you/your computer get now assigned a new IP-address.
Windows95 itself does NOT include any DHCP-server, you need to connect to a
Windows NT (or similar class) server , which is configured as DHCP-server.

Microsoft supplies now with Windows98/ME and with Windows 2000/XP a
feature for
IP-Auto-Configuration without a DHCP-server on the network.

DHCP-server may also be buildin to some other products ( example : software
Router for
Internet Connection Sharing ) .

If you are using/intend to use "obtain an IP address automatically", please do NOT
reply
on it without verifying, that you did get an IP-address assigned.
Please make the check using either "winipcfg" , "ipconfig" or view the Status
information.

Looks simple until now ? Actually there is already a lot more 'hidden' actions:
The systems have IP-addresses, but Ethernet-boards ONLY know their Ethernet-
address, so as soon as a TCP/IP configured system is switched on, it is advertising

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its presence onto the network:" Hey, I am alive, my Ethernet address is '08000b
0a0238' and my IP-address is '192.168.10.2' ". , and each TCP/IP system on the
network builds up a table with all this information, which is usually
checked/verified in time-intervals of 15 min.

If your system needs now to communicate with a station, for which it does NOT
have an entry in its table of IP/Ethernet-Addresses, it sends out a search-message
to everybody ("Broadcast-Message") like: " Hey, I like to communicate with the
IP-address '192.168.10.4', but I do NOT know your Ethernet-Address. Please,
identify yourself". This causes the system with the requested IP-address to send out
its advertising again.

These processes are called ARP (Address Resolution Protocol) and RARP
(Reversed Address Resolution Protocol).

This ARP/RARP works fine on a local-area-network (on an Ethernet network), but
will NOT work for Internet communications, because:
- the Database of Ethernet-to-IP-address would need to have 10+ Million entries
- the Internet would only be busy with ARP/RARP.

Gateway/Router:
To connect a TCP/IP local-area-network to another TCP/IP LAN (which could be
the complete Internet) or via a Wide-Area-Network (WAN), you need now a
device called : Gateway or Router

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You need to tell Windows95 about the Gateway in the TCP/IP-properties:

Now, also the 'Subnet-Mask', which is usually '255.255.255.0', becomes important:
if you now like to connect to 207.68.137.53 (which is the Website of Microsoft),
TCP/IP checks your own IP-address and the IP-address of the destination against
the Subnet-mask. Lets do that comparison on a binary level:

System: IP/subnet-mask Binary
your system 192.168.10.1 11000000 10101000 00001010 00000001
local server 192.168.10.10 11000000 10101000 00001010 00001010
Microsoft 207.68.137.53 11001111 01000100 10001001 00110101
Subnet-mask 255.255.255.0 11111111 11111111 11111111 00000000

TCP/IP compare now the part of the addresses, defined by the '1's in the subnet-
mask

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( or simple: the part of the IP-addresses, where the subnet-mask is 255 ):
xxx indicates, that this part of an IP-address does not matter anymore :

System: IP/subnet-mask Binary
your system 192.168.10.xxx 11000000 10101000 00001010 xxxxxxxx
local server 192.168.10.xxx 11000000 10101000 00001010 xxxxxxxx
Microsoft 207.68.137.xxx 11001111 01000100 10001001 xxxxxxxx
Subnet-mask 255.255.255.0 11111111 11111111 11111111 00000000

if your system connects to another system on the same network (like a local server,
in this
example at 192.168.10.10) , that part of the address (the first 24-bits in this
example) are the same,
( 192.168.10.xxx ) so TCP/IP looks up the Ethernet address in its ARP table and
connects directly
to that system.
But if there is a difference in these 24-bits, then TCP/IP connects to the Gateway
(in this example: 192.168.10.20), and it is now the job of the Gateway to establish
somehow the connection to the destination system (somewhere inside that Internet
'cloud'). The Gateway/Router keeps for that purpose special tables and passed on
the request to the next router, which itself goes to the next, which itself goes to the
next,....., until you reach the destination.
( If you have on your network multiple gateways/routers (maybe one for a
permanent Internet connection and
another for a company internal WAN), you need to program the systems to select

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the proper gateway using the
ROUTE-command )

Each Router/gateway on the network (which could be the Internet or a Wide-Area-
Network WAN)
passes on the message, until it reaches its destination, and the reply comes back the
same way
(for more details on Routing: Setup TCP/IP Routing ).

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The above assumes, that all systems have an IP-address, which is valid on the
Internet !
If you connect via dialup-connection to the Internet, but like to use the connection
on
multiple systems on a network, you need a Proxy
When explaining the use of a Gateway / Router, I usually use this story:

Compare it to sending out invitations to a party :

You have decided to celebrate your birthday (or something else ).
You will invite your good friends, your neighbors (because your party may become
a little noisy, so it is better to invite them ) and some relatives.
You design a nice invitation letter and print it.

How will you deliver it to your neighbors ?
Most probably you will simply walk over in the evening and drop it yourself
in the mailbox of your neighbor.

But your brother/sister lives on another continent !
Will you make a direct delivery ? Most probably no.
You will put the invitation in an envelope, write the address on there and drop it
into
the next collection box of your postal service. They will come (maybe with a car,
maybe
on a bike), bring it to the next post-office, then on a truck to the next railroad

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station to
the next airport, then onto a plane, again a truck, again a car/bike, until it arrives at
your brother/sister.

The delivery via postal-service is equivalent to the TCP/IP Gateway/Router :
You just drop your message and then you do not care anymore, it is now the
job of the postal-service (for your invitation letter) or the Gateway/Router (for your
TCP/IP Network traffic) to make sure that it arrives at the proper destination.

You can check this yourself: open on Win95 a DOS-window and run the 'tracert'
command (which is installed as part of the TCP/IP protocol).
In my example, I traced the router to "ourworld.compuseve.com":

TRACERT 149.174.213.39 :

HOSTS/LMHOSTS:
it is difficult to remember IP-addresses, it is much easier to remember names (and
having the computer lookup the name and find the IP-address). That is the purpose
of the 'HOSTS'-file and 'LMHOSTS'-file: Windows95 TCP/IP installs in
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"C:\WINDOWS" a file called 'hosts.sam' and 'lmhosts.sam', rename/copy it to
'hosts'/'lmhosts' and then use it to define the names:

all lines starting with an '#' are comment lines.
The formatting of 'hosts' and 'lmhosts' is the same:
IP-address, some spaces, computername
example:
-> used for internal purposes (loopback), do
172.0.0.1 localhost NOT delete
192.0.0.150 p120 -> refering to a system on the local network
207.68.137.53 www.microsoft.com -> such Internet-Websites URL's are just
names for an IP-address

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When to use HOSTS and when to use LMHOSTS ?
That is a confusing subject: having 2 files with a very similar job.
HOSTS is read by basic TCP/IP software (ping, ftp, ......)
LMHOSTS is used by the Microsoft Networking/Client/Workgroup management. If
systems are on the same cable segment, the system broadcast their presence and
find each other automatically, no need to enter anything in LMHOSTS.
However, such broadcast-packets to NOT get routed. Adding then the IP-address
manually in LMHOSTS makes the system aware about a system on different
segments.
NOTE: LMHOSTS originates from "Lan Manager HOSTS", a name from the
history of Microsoft networks.
An example for using LMHOSTS : Connection via a Router to a NT Domain
Server

DNS:
Too much work to typ these IP-addresses ?
Looks like another item for automation, and exactly that is DNS : Domain Name
Service:
it allows to use names instead of IP-addresses, but you need to configure it as part

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of the TCP/IP-properties:

If you now define an address ( like: www.microsoft.com or someserver.com in the
picture below)
TCP/IP will make:
1: a call out to a DNS-server, asking for the IP of someserver.com
2: the DNS server will reply with the IP-address (in this example 192.5.6.111)
3: TCP/IP makes now the connection to the requested server someserver.com,
using the IP-address 192.5.6.111 :

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Port:
TCP/IP is a complex protocol, offering multiple services (especially on the
Internet), like:
- HTTP (=Web-Browsing)
- FTP
- e-mail
- file sharing
For each of these services, a port is used for the specific type of communication
(advanced TCP/IP)
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It is possible to have Multiple IP-addresses on a Network Card.

HUB

A network hub is a fairly unsophisticated broadcast device. Hubs do not
manage any of the traffic that comes through them, and any packet entering any
port is broadcast out on all other ports.

Definition:

 In computer networking, a hub is a small, simple, inexpensive device that
joins multiple computers together. Many network hubs available today
support the Ethernet standard. Other types including USB hubs also exist,
but Ethernet is the type traditionally used in home networking.

Working with Ethernet Hubs

To network a group of computers using an Ethernet hub, first connect an Ethernet
cable into the unit, and then connect the other end of the cable to each computer's

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network interface card (NIC). All Ethernet hubs accept the RJ-45 connectors of
standard Ethernet cables.

To expand a network to accommodate more devices, Ethernet hubs can also be
connected to each other, to switches, or to routers.

Characteristics of Ethernet Hubs

Ethernet hubs vary in the speed (network data rate or bandwidth) they support.
Some years ago, Ethernet hubs offered only 10 Mbps rated speeds. Newer types of
hubs offer 100 Mbps Ethernet. Some support both 10 Mbps and 100 Mbps (so-
called dual-speed or 10/100 hubs).

The number of ports an Ethernet hub supports also varies. Four- and five-port
Ethernet hubs are most common in home networks, but eight- and 16-port hubs can
be found in some home and small office environments.

Older Ethernet hubs were relatively large in size and sometimes noisy as they
contained built in fans for cooling the unit. Newer devices are much smaller,
designed for mobility, and noiseless.

When to Use an Ethernet Hub

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Ethernet hubs operate as Layer 2 devices in the OSI model, the same as network
switches. Although offering comparable functionality, nearly all mainstream home
network equipment today utilizes network switch technology instead of hubs due
to the performance benefits of switches. A hub can be useful for temporarily
replacing a broken network switch or when performance is not a critical factor on
the network.

Definition:

 A network switch is a small hardware device that joins multiple computers
together within one local area network (LAN). Technically, network
switches operate at layer two (Data Link Layer) of the OSI model.

Network switches appear nearly identical to network hubs, but a switch generally
contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs,
network switches are capable of inspecting data packets as they are received,
determining the source and destination device of each packet, and forwarding them
appropriately. By delivering messages only to the connected device intended, a
network switch conserves network bandwidth and offers generally better
performance than a hub.

As with hubs, Ethernet implementations of network switches are the most
common. Mainstream Ethernet network switches support either 10/100 Mbps Fast
Ethernet or Gigabit Ethernet (10/100/1000) standards.

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Different models of network switches support differing numbers of connected
devices. Most consumer-grade network switches provide either four or eight
connections for Ethernet devices. Switches can be connected to each other, a so-
called daisy chaining method to add progressively larger number of devices to a
LAN.

INTERNETWORK

An Internet work is the connection of two or more distinct computer
networks or network segments via a common routing technology. The result is
called an internet work.

INTRANET
An intranet is the internal network of an organization.

EXTRANET

BASIC TERMINOLOGIES

COMPUET NETWORK

A computer network is the infrastructure that allows two or more computers
(called hosts) to communicate with each other.

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PROTOCOL
A set of rules for communication between two or more computers.

NODE
A node is usually itself a computer (general or special) which runs specific
network software.

COMMUNICATION LINES

The communication lines may take many different shapes and forms, even in
the same network. Examples include: copper wire cables, optical fiber, radio
channels, and telephone lines.

PACKET
A short message sent between networks.

OSI MODEL

Open System Interconnection, a reference model developed by International
Standard Organization.

TCP

Transmission Control Protocol. A connection oriented protocol.

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UDP
User Datagram Protocol. A connection-less protocol.

LAN

Large Area Network.

WAN

Wide Area Network.
MAN

Metropolitan Area Network.

PAN

Personal Area Network.

VPN

Virtual Private Network.

Client

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The node which sends the request to the server.
Server

The node which accepts the request from the client node, process and sent back
the reply to the client.

A Family of Protocols

TCP/IP is a large collection of different communication protocols based upon the
two original protocols TCP and IP.

TCP - Transmission Control Protocol

TCP is used for transmission of data from an application to the network.

TCP is responsible for breaking data down into IP packets before they are sent, and
for assembling the packets when they arrive.

IP - Internet Protocol

IP takes care of the communication with other computers.

IP is responsible for the sending and receiving data packets over the Internet.
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HTTP - Hyper Text Transfer Protocol

HTTP takes care of the communication between a web server and a web browser.

HTTP is used for sending requests from a web client (a browser) to a web server,
returning web content (web pages) from the server back to the client.

HTTPS - Secure HTTP

HTTPS takes care of secure communication between a web server and a web
browser.

HTTPS typically handles credit card transactions and other sensitive data.

SSL - Secure Sockets Layer

The SSL protocol is used for encryption of data for secure data transmission.

SMTP - Simple Mail Transfer Protocol

SMTP is used for transmission of e-mails.

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MIME - Multi-purpose Internet Mail Extensions

The MIME protocol lets SMTP transmit multimedia files including voice, audio,
and binary data across TCP/IP networks.

IMAP - Internet Message Access Protocol

IMAP is used for storing and retrieving e-mails.

POP - Post Office Protocol

POP is used for downloading e-mails from an e-mail server to a personal
computer.

FTP - File Transfer Protocol

FTP takes care of transmission of files between computers.

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NTP - Network Time Protocol

NTP is used to synchronize the time (the clock) between computers.

DHCP - Dynamic Host Configuration Protocol

DHCP is used for allocation of dynamic IP addresses to computers in a network.

SNMP - Simple Network Management Protocol

SNMP is used for administration of computer networks.

LDAP - Lightweight Directory Access Protocol

LDAP is used for collecting information about users and e-mail addresses from the
internet.

ICMP - Internet Control Message Protocol

ICMP takes care of error-handling in the network.

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ARP - Address Resolution Protocol

ARP is used by IP to find the hardware address of a computer network card based
on the IP address.

RARP - Reverse Address Resolution Protocol

RARP is used by IP to find the IP address based on the hardware address of a
computer network card.

BOOTP - Boot Protocol

BOOTP is used for booting (starting) computers from the network.

PPTP - Point to Point Tunneling Protocol

PPTP is used for setting up a connection (tunnel) between private networks.

REPEATER

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A repeater is an electronic device that receives a signal and retransmits it at a
higher level and/or higher power, or onto the other side of an obstruction, so that
the signal can cover longer distances.

BRIDGES
Bridges tend to be more complex than hubs or repeaters. Bridges can
analyze incoming data packets to determine if the bridge is able to send the given
packet to another segment of the network.

HUB

A network hub is a fairly unsophisticated broadcast device. Hubs do not
manage any of the traffic that comes through them, and any packet entering any
port is broadcast out on all other ports.

REFERENCE:

BOOKS:

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[1]. Computer Networking: A Top-Down Approach (5th Edition) by James F.
Kurose. This review is from: Computer Networks (4th Edition), Author Andrew S.
Tanenbaum.

[2]. Computer Network Concepts: (6th Edition) Author Willam Stalling.

WEBSITES:

[1]. Http://www.Amazon.com

[2]. Http://www.About.com

[3]. Http://www.wikepedia.com

[4]. Http://www.Protocol.com

[5]. Http://www.osimodel.com

[6]. Http://www.googlesearch.com

[7]. Http://www.wikepedia.com

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[8]. Http://www.networksprotocls.com

[9]. Http://www.networktopologies.com

[10]. Http://www.tcp/ip network.com