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Definition

Two or more computers that are linked in order to share resources such as printers and CD-ROMs, exchange files, or allow electronic communications are called as networked computers. The computers on a computer network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

 Computer network can be classified on the basis of following features :

•  By Scale: Computer networks may be classified according to the scale :  
•     Local Area Network (LAN)

•     Metropolitan Area Network (MAN)

•     Wide Area Network (WAN)

•  By Connection Method: Computer networks can also be classified according to the hardware technology that is used to connect the individual devices in the network such as Optical fibre, Ethernet, Wireless LAN.

• By Functional Relationship (Network Architectures) : Computer networks may be classified according to the functional relationships which exist between the elements of the network. This classification also called computer architecture. There are two type of network architecture :
•  Client-Server

•     Peer-to-Peer Architecture

• By Network Topology: Network Topology signifies the way in which intelligent devices in the network see their logical or physical relations to one another. Computer networks may be classified according to the network topology upon which the network is based, such as :

•     Bus Topology

•     Star Topology

•     Ring Topology

•     Mesh Topology

•     Star-Bus Topology

•     Tree or Hierarchical Topology

Advantages of Network

The following are the distinct notes in favor of computer network.

1. The computers, staff and information can be well managed
2. A network provides the means to exchange data among the computers and to make programs and data available to people
3. It permits the sharing of the resources of the machine
4. Networking also provides the function of back-up.
5. Networking provides a flexible networking environment. Employees can work at home by using through networks ties through networks into the computer at office.

Disadvantages of Computer Network

Following are the disadvantages of computer network:

• Security issue: It is done for service sharing which can bring lots of security issues.
• Prone to virus, hacker
• Difficult to mange traffic and congestion control
• Some networks are sophisticated that requires huge time and money

Network Services

Network services are the thing that a network can do. The major networking services are

1. File Services: This includes file transfer, storage, data migration, file update, synchronization and achieving.
2. Printing Services: This service produces shared access to valuable printing devices.
3. Message Services: This service facilitates email, voice mails and coordinate object oriented applications.
4. Application Services: This services allows to centralize high profile applications to increase performance and scalability
5. Database Services: This involves coordination of distributed data and replication.

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Internet Protocol version 6 (IPv6)  is  the  latest  revision  of  the Internet  Protocol (IP),  days
of  IPv6  protocol  development  stage  the communications  protocol that  routes  traffic  across
the Internet.  IP  stands  for  Internet  Protocol  which  is  one  of  the  main  pillars  that  supports  the
Internet
There
called  IPng  in  the  early.  It  is  intended  to  replace IPv4.  IPv6  was  developed  by  the Internet
Engineering  Task  Force (IETF)  to  deal  with  the  long-anticipated  problem  of IPv4  address
exhaustion.

Every  device  on  the  Internet,  such  as  a  computer  or  mobile  telephone,  must  be  assigned
an IP  address for  identification  and  location  addressing  in  order  to  communicate  with  other
devices.  With  the  ever-increasing  number  of  new  devices  being  connected  to  the  Internet,
the  need  arose  for  more  addresses  than  IPv4  is  able  to  accommodate.  IPv6  uses  a  128-
bit address,  allowing  2128,  or  approximately 3.4×1038 addresses,  or  more  than 7.9×1028 times
as  many  as  IPv4,  which  uses  32-bit  addresses.  IPv4  allows  only  approximately  4.3  billion
addresses.  IPv6  provides  enough  addresses  to  allow  the  Internet  to  continue  to  expand  and  the
industry  to  innovate.  It  is  not,  however,  directly  compatible  with  IPv4,  meaning  that  a  device
connected  via  IPv4  cannot  communicate  directly  with  a  device  connected  using  IPv6.  IPv6
addresses
3001:Fdb8:C5a1:0071:3100:4a1b:0070:1331.

During  the  late  1980s  (88-89)  Internet  has  started  to  grow  exponentially.  The  ability  to  scale
Internet for future demands requires a limitless supply of IP addresses and improved mobility. In
1991
to develop a new protocol for Internet. In 1994 IETF gave a clear direction of IPng or IPv6 after
a long process of discussion.

Benefits of IPv6:

More Efficient Routing: IPv6  reduces  the  size  of  routing  tables  and  makes  routing  more
efficient  and  hierarchical.  IPv6  allows  ISPs  to  aggregate  the  prefixes  of  their  customers'
networks

More Efficient Packet Processing: IPv6's  simplified  packet  header  makes  packet  processing
more efficient. Compared with IPv4, IPv6 contains no IP-level checksum, so the checksum does
not
because most link-layer technologies already contain checksum and error-control capabilities.

Directed Data Flows: IPv6  supports  multicast  rather  than  broadcast.  Multicast  allows
bandwidth-intensive  packet  flows  (like  multimedia  streams)  to  be  sent  to  multiple  destinations

simultaneously, saving network bandwidth. Disinterested hosts no longer must process broadcast
packets.

Simplified Network Configuration: Address  auto-configuration  (address  assignment)  is  built
in to IPv6. A router will send the prefix of the local link in its router advertisements. A host can
generate
Universal Identifier (EUI) 64-bit format, to the 64 bits of the local link prefix.

Security: IPSec, which provides confidentiality, authentication and data integrity, is baked into
in  IPv6.  Because  of  their  potential  to  carry  malware,  IPv4  ICMP  packets  are  often  blocked  by
corporate  firewalls,  but  ICMPv6,  the  implementation  of  the  Internet  Control  Message  Protocol
for

• August 1990
– First wakeup call by Solensky in IETF on IPv4 address exhaustion
• December 1994
–
[RFC1719]
• December 1994
–
• January 1995
–
• December 1995
–
• December 1998
–

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Network Address Translation (NAT)

            Network Address Translation (NAT) is a method of connecting multiple computers to the Internet (or any other IP network) using one IP address. This allows home users and small businesses to connect their network to the Internet cheaply and efficiently. NAT is necessary when the number of IP addresses assigned to you by your Internet Service Provider is less than the total number of computers that you wish to provide Internet access for.

Advantage of Using NAT:

• Use of a single registered IP address for an entire network
• Independence of ISP IP addresses
• Transparent to end systems in some cases (increased security)
• Delays need for IPv4 replacement
• Mask the true internal IP addresses of the internal network.

Disadvantages of NAT:

• Breaks end-to-end model (the private IP space might already be in use)
• Enables end-to-end address conflicts (encourages poor address management)
• Increases local support burden and complexity
• Certain applications do not work properly in conjunction
• Applications needing encryption and key exchange might be problematic
• Increases the probability of misaddressing
• It might require more work if assigning registered IPs to private IPs
• Possible performance degradation if you get close to the limit of about 25,000 connections
• Obscures the ability to manage from the public side of the NAT box.

Solving IPv4 Address Exhaustion

The problem can be solved in two ways:

1) Extending NAT Architecture
       - IP Next Layer (IPNL)
       - Preserves characteristics of IPv4
2) Transition to  IPv6
        - Much bigger address space

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