Networking:
Networking means connecting two or
more devices (nodes) for communication purpose. A node can be a computer,
printer, or any other device capable of sending and/or receiving data generated
by other nodes on the network.
Computer Network:
A computer network is a group of interconnected computer or A computer network is any set of
computers or devices connected to each other with the ability to exchange data.
Types of networks:
Local Area Network (LAN): A network covering a small geographic
area, like a home, office, or building. Current LANs are most likely to be
based on Ethernet technology. For example, a library may have a wired or
wireless LAN for users to interconnect local devices (e.g., printers and
servers) and to connect to the internet. On a wired LAN, PCs in the library are
typically connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol
through a system of interconnection devices and eventually connect to the
internet.
Metropolitan Area Network (MAN): A Metropolitan Area Network 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.
Wide Area Network
(WAN): A WAN is a data communications network that covers a
relatively broad geographic area (i.e. one city to another and one country to
another country) and that often uses transmission facilities provided by common
carriers, such as telephone companies.
Global Area Network
(GAN): Global area networks (GAN) specifications are 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.
Internetwork: Two or more
networks or network segments connected using devices, such as a router. Any
interconnection among or between public, private, commercial, industrial, or
governmental networks may also be defined as an internetwork. In modern
practice, the interconnected networks use the Internet Protocol. There are at
least three variants of internetwork, depending on who administers and who
participates in them:
- Intranet
- Extranet
- Internet
Intranet: An intranet is a set of networks,
using the Internet Protocol and IP-based tools such as web browsers and file
transfer applications, that is 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.
Extranet: An extranet is a network or
internetwork 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 (e.g. a
company's customers may be given access to some part of its intranet creating
in this way an extranet, while at the same time the customers may not be
considered 'trusted' from a security standpoint). Technically, an extranet may
also be categorized as a CAN, MAN, WAN, or other type of network, although, by
definition, an extranet cannot consist of a single LAN; it must have at least
one connection with an external network.
Internet: The
Internet is a specific internetwork. It 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 internetworks.
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. Service providers and large
enterprises exchange information about the reachability of their address spaces
through the Border Gateway Protocol (BGP), forming a redundent world-wide mesh
of transmission paths.
Network
topology:
Computer networks may be classified according to
the network topology upon which the network is based, such as Bus network, Star
network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical
topology network, etc.Network Topology signifies the way in which devices in
the network see their logical relations to one another. The use of the term
"logical" here is significant. That is, network topology is independent
of the "physical" layout of the network. Even if networked computers
are physically placed in a linear arrangement, if they are connected via a hub,
the network has a Star topology, rather than a Bus Topology. In this regard the
visual and operational characteristics of a network are distinct; the logical
network topology is not necessarily the same as the physical layout.
Open Systems and the Open Systems Interconnection (OSI) model:
A set of protocols
that would allow any two different systems to communicate regardless of their
underlying architecture is called an open system. The ISO has addressed the
problem of allowing many devices to communication and has developed its Open
System Interconnect (OSI) model. If fully developed, it would allow any two
computers to communicate provided they are connected.
In its most basic form, it divides network
architecture into seven layers which, from top to bottom, are the Application,
Presentation, Session, Transport, Network, Data-Link, and Physical Layers. It
is therefore often referred to as the OSI Seven Layer.
Description of Open Systems Interconnection(OSI) layers
OSI
Model
|
|||
Data
unit
|
Layer
|
Function
|
|
Host
layers |
Data
|
1. Application
|
Network
process to application
|
2. Presentation
|
Data
representation and encryption
|
||
3. Session
|
Interhost
communication
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||
Segment/Datagram
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4. Transport
|
End-to-end
connections and reliability
|
|
Media
layers |
Packet
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5. Network
|
Path
determination and logical addressing
|
Frame
|
6. Data Link
|
Physical
addressing (MAC & LLC)
|
|
Bit
|
7. Physical
|
Media,
signal and binary transmission
|
|
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. It allows users to connect
to each other either by using cables or wirelessly.
1.Repeaters: repeater is an electronic device that receives a signal
and retransmits it at a higher level or higher power, or onto the other side of
an obstruction, so that the signal can cover longer distances without
degradation. In most twisted pair Ethernet configurations, repeaters are
required for cable runs longer than 100 meters.
2.Hubs: hub contains multiple ports. When a packet
arrives at one port, it is copied to all the ports of the hub for transmission.
When the packets are copied, the destination address in the frame does not
change to a broadcast address. It does this in a rudimentary way, it simply
copies the data to all of the Nodes connected to the hub.
3.Bridges: A network bridge connects multiple network
segments at the data link layer (layer 2) of the OSI model. Bridges do not
promiscuously copy traffic to all ports, as hubs do, but learns which MAC
addresses are reachable through specific ports. Once the bridge associates a
port and an address, it will send traffic for that address only to that port.
Bridges do send broadcasts to all ports except the one on which the broadcast
was received. Bridges learn the association of ports and addresses by examining
the source address of frames that it sees on various ports. Once a frame
arrives through a port, its source address is stored and the bridge assumes
that MAC address is associated with that port. The first time that a previously
unknown destination address is seen, the bridge will forward the frame to all
ports other than the one on which the frame arrived.
Bridges
come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- 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 by routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
4.Switches: A switch is a device that performs
switching. Specifically, it forwards and filters OSI layer 2 datagrams (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 datagrams 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 (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 that
most or all of the network be connected directly to a switch, or another switch
that is in turn connected to a switch.
5.Routers: Routers are networking devices that
forward data packets between networks using headers and forwarding tables to
determine the best path to forward the packets. Routers work at the network
layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide
interconnectivity between like and unlike media (RFC 1812). This is
accomplished by examining the Header of a data packet, and making a decision on
the next hop to which it should be sent (RFC 1812) They use preconfigured
static routes, status of their hardware interfaces, and routing protocols to
select the best route between any two subnets. A router is connected to at
least two networks, commonly two LANs or WANs or a LAN and its ISP's network.
Some DSL and cable modems, for home (and even office) use, have been integrated
with routers to allow multiple home/office computers to access the Internet
through the same connection. Many of these new devices also consist of wireless
access points (waps) or wireless routers to allow for IEEE 802.11b/g wireless
enabled devices to connect to the network without the need for a cabled
connection.
Protocols:
A protocol is a set of rules that
governs data communication to occur. It defines the format and the order of
message exchanged between two or more communication entities, as well as the
actions taken on the transmission and/or receipt of a message or other event. A
protocol defines what is communicated, how it is communicated, and when it is
communicated. Without protocol two computer can be connected but not
communicate. It is essential to use same protocol for communication between two
devices. When several protocols work at a time it is called protocol suit. At
present three widely used protocol suits are TCP/IP, IPX/SPX and AppleTalk.
Connection-Oriented and Connectionless services:
When an application uses the
connection-oriented service, the client program and the server program send
control packets to each other before sending packets with the actual data to be
transferred. This so called handshaking procedure alerts client and server,
allowing them to prepare for an onslaught of data packets. Once the handshaking
procedure is finished, a connection is said to be established between the two
end systems. The Internet connection oriented service has a name
-Transmission Control Protocol
(TCP); the initial version of TCP protocol is defined in the Internet Request
for Comments RFC 793.
There is no handshaking with the
Internet’s connectionless service. When one side of an application wants to
send packets to other side of the application, the sending program simply sends
the packets. Since there is no handshaking procedure prior to data packet
transmission, data can be deliver sooner. A source never knows for sure which
packets have arrived at the destination. The Internet’s connectionless service
is called User Datagram Protocol (UDP); UDP is define in the Internet Request
for Comments RFC 768.
Routing Protocols: A routing protocol sends and receives routing
information packets to and from other routers. Routing protocols implement
algorithms that tell routers the best paths through internetworks. Routing
protocols include Border Gateway Protocol (BGP), Interior Gateway Routing
Protocol (IGRP), Routing Information Protocol, and Open Shortest Path First
(OSPF) to name a few. Routing protocols provide the layer 3 network state
update.
Routed Protocols: A routed protocol can be routed by a router,
which means that it can be forwarded from one router to another. Such as
Internet Protocol (IP), Novell Internetwork Packet eXchange (IPX), and
AppleTalk are routed protocols.
In short, routing protocols
route datagrams through a network. Routing is a layer 3 function, thus, routing
and routed protocols are network-layer entities. Routing tables on the layer 3
switch (router) are populated by information from routing protocols. A routed
protocol will enter an interface on a router, be placed in a memory buffer,
then it will be forwarded out to an interface based on information in the
routing table.
Routed versus routing protocols:
Confusion often arises between routing protocols and routed
protocols. While routing protocols help the router in the decision-making
on which paths to send traffic, routed protocols are responsible for the actual
transfer of traffic between Layer3 devices. Specifically, a routed protocol is
any network protocol that provides enough information in its network layer
address to allow a packet to be forwarded from one host to another host based
on the addressing scheme, without knowing the entire path from source to
destination. Routed protocols define the format and use of the fields
within a packet. Packets generally are conveyed from end system to end system.
Internet Address or IP:
IP address is a network layer
protocol address for a host in a TCP/IP network. IP address is used to uniquely
identify each host in a network. An IP address in the current version of protocol
is a 32-bit binary address that uniquely and universally defines the connection
of a host or a router to the Internet. IP address is needed in order to
communicate with other hosts in the network using the TCP/IP suite of
protocols.
IP Addresses are Unique:
The IP addresses are unique in
the sense of that each address define one, and only one, connection in the Internet
Two device on the internet can never have the same address at the same
time. However, if a device has two
connections to the Internet, via two networks, it has two IP address.
IP Addresses are Universal:
The IP addresses are Universal in
the sense that the addressing system must be accepted by any host that wants to
connected to the Internet.
Originally,
an IP address was defined as a 32-bit number and this system, now
named Internet Protocol Version 4 (IPv4), is still in use today. However, due
to the enormous growth of the Internet and the resulting depletion of the
address space, a new addressing system (IPv6), using 128 bits for the address,
had to be developed. IPv6 is now being deployed across the world; in many
places it coexists with the old standard and is transmitted over the same
hardware and network links. This
document only covers IPv4.
There are two common notations to show an
IP address: Binary notation and dotted decimal notation.
In binary notation, the IP address is displayed as
32 bits. To make the address more readable, one or more spaces is usually
inserted between each octet (8 bit). The following example of an IP address. In
binary notation: 11000000 10101000
00000000 00000011.
In decimal notation: 192.168.0.3
Each IP address divided into two parts: Network ID or Netid + Host ID or Hostid
In a specific network, Network ID of each IP address is same
but Host ID must be different.
IP versions
Two versions of the Internet Protocol (IP) are in use: IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5.IPv4 addresses
Main article: IPv4#Addressing
IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations.
IPv4 subnetting
In the early stages of development of the Internet Protocol,[1] network administrators interpreted an IP address in two parts: network number portion and host number portion. The highest order octet (most significant eight bits) in an address was designated as the network number and the remaining bits were called the rest field or host identifier and were used for host numbering within a network.This early method soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the Internet addressing specification was revised with the introduction of classful network architecture.[2]
Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the class of the address. Three classes (A, B, and C) were defined for universal unicast addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes (B and C). The following table gives an overview of this now obsolete system.
Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.
IPv4 private addresses
Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally unique IP addresses. Three ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.
Today, when needed, such private networks typically connect to the Internet through network address translation (NAT).
| Start | End | No. of addresses | |
|---|---|---|---|
| 24-bit block (/8 prefix, 1 × A) | 10.0.0.0 | 10.255.255.255 | 16777216 |
| 20-bit block (/12 prefix, 16 × B) | 172.16.0.0 | 172.31.255.255 | 1048576 |
| 16-bit block (/16 prefix, 256 × C) | 192.168.0.0 | 192.168.255.255 | 65536 |
IPv4 address exhaustion
IPv4 address exhaustion is the decreasing supply of unallocated Internet Protocol Version 4 (IPv4) addresses available at the Internet Assigned Numbers Authority (IANA) and the regional Internet registries (RIRs) for assignment to end users and local Internet registries, such as Internet service providers. IANA's primary address pool was exhausted on February 3, 2011 when the last 5 blocks were allocated to the 5 RIRs.[5][6] APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, intended to be allocated in a restricted process[7]IPv6 addresses
Main article: IPv6 address
The new design is not intended to provide a sufficient quantitysign is not intended to provide a sufficient quantity of addresses on its own, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 264 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment — that is the local administration of the segment's available space — from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or renumbering.
The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in Classless Inter-Domain Routing (CIDR).
Many modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers, voice over IP (VoIP) and multimedia equipment, and network peripherals.
IPv6 private addresses
Just as IPv4 reserves addresses for private or internal networks, blocks of addresses are set aside in IPv6 for private addresses. In IPv6, these are referred to as unique local addresses (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for this block which is divided into two /8 blocks with different implied policies The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.[8]Early designs used a different block for this purpose (fec0::), dubbed site-local addresses.[9] However, the definition of what constituted sites remained unclear and the poorly defined addressing policy created ambiguities for routing. This address range specification was abandoned and must not be used in new systems.[10]
Addresses starting with fe80:, called link-local addresses, are assigned to interfaces for communication on the link only. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have a communication path via their link-local IPv6 address. This feature is used in the lower layers of IPv6 network administration (e.g. Neighbor Discovery Protocol).
None of the private address prefixes may be routed on the public Internet.
IP subnetworks
IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is logically recognized as consisting of two parts: the network prefix and the host identifier, or interface identifier (IPv6). The subnet mask or the CIDR prefix determines how the IP address is divided into network and host parts.The term subnet mask is only used within IPv4. Both IP versions however use the Classless Inter-Domain Routing (CIDR) concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively. The CIDR notation for the same IP address and subnet is 192.0.2.1/24, because the first 24 bits of the IP address indicate the network and subnet.
IP address assignment
Internet Protocol addresses are assigned to a host either anew at the time of booting, or permanently by fixed configuration of its hardware or software. Persistent configuration is also known as using a static IP address. In contrast, in situations when the computer's IP address is assigned newly each time, this is known as using a dynamic IP address.Methods
Static IP addresses are manually assigned to a computer by an administrator. The exact procedure varies according to platform. This contrasts with dynamic IP addresses, which are assigned either by the computer interface or host software itself, as in Zeroconf, or assigned by a server using Dynamic Host Configuration Protocol (DHCP). Even though IP addresses assigned using DHCP may stay the same for long periods of time, they can generally change. In some cases, a network administrator may implement dynamically assigned static IP addresses. In this case, a DHCP server is used, but it is specifically configured to always assign the same IP address to a particular computer. This allows static IP addresses to be configured centrally, without having to specifically configure each computer on the network in a manual procedure.In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using state-less auto-configuration methods, such as Zeroconf.
Uses of dynamic addressing
Dynamic IP addresses are most frequently assigned on LANs and broadband networks by Dynamic Host Configuration Protocol (DHCP) servers. They are used because it avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows many devices to share limited address space on a network if only some of them will be online at a particular time. In most current desktop operating systems, dynamic IP configuration is enabled by default so that a user does not need to manually enter any settings to connect to a network with a DHCP server. DHCP is not the only technology used to assign dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the Point-to-Point Protocol.Sticky dynamic IP address
A sticky dynamic IP address is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address which seldom changes. The addresses are usually assigned with DHCP. Since the modems are usually powered on for extended periods of time, the address leases are usually set to long periods and simply renewed. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address.Address autoconfiguration
RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the block fe80::/10.These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet.
When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft created an implementation that is called Automatic Private IP Addressing (APIPA). Due to Microsoft's market power, APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses.
Uses of static addressing
Some infrastructure situations have to use static addressing, such as when finding the Domain Name System (DNS) host that will translate domain names to IP addresses. Static addresses are also convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a time to live, or caching time, after which it should be looked up to confirm that it has not changed. Even static IP addresses do change as a result of network administration (RFC 2072)Public addresses
A public IP address in common parlance is synonymous with a, globally routable unicast IP address.[citation needed]Both IPv4 and IPv6 define address ranges that are reserved for private networks and link-local addressing. The term public IP address often used exclude these types of addresses.
Modifications to IP addressing
IP blocking and firewalls
Firewalls perform Internet Protocol blocking to protect networks from unauthorized access. They are common on today's Internet. They control access to networks based on the IP address of a client computer. Whether using a blacklist or a whitelist, the IP address that is blocked is the perceived IP address of the client, meaning that if the client is using a proxy server or network address translation, blocking one IP address may block many individual computers.IP address translation
Multiple client devices can appear to share IP addresses: either because they are part of a shared hosting web server environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a request. A common practice is to have a NAT hide a large number of IP addresses in a private network. Only the "outside" interface(s) of the NAT need to have Internet-routable addresses.[11]Most commonly, the NAT device maps TCP or UDP port numbers on the outside to individual private addresses on the inside. Just as a telephone number may have site-specific extensions, the port numbers are site-specific extensions to an IP address.
In small home networks, NAT functions usually take place in a residential gateway device, typically one marketed as a "router". In this scenario, the computers connected to the router would have 'private' IP addresses and the router would have a 'public' address to communicate with the Internet. This type of router allows several computers to share one public IP address.
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