Network Technology

        UNIT - 1

 =>Advanced Network Topologies Ethernet, CDDI, FDDI

Ethernet:

• Ethernet is a way of connecting computers together in a local area network or LAN. It has been the most widely used method of linking computers together in LANs since the 1990s.
•  The basic idea of its design is that multiple computers have access to it and can send data at any time.
• It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3, and has since been refined to support higher bit rates and longer link distances.
• Over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI and ARCNET.
• Ethernet evolved to include higher bandwidth, improved media access control methods, and different physical media. The coaxial cable was replaced with point-to-point links connected by Ethernet repeaters or switches.

CDDI:

• For a local area network (LAN), CDDI (Copper Distributed Data Interface) is a standard for data transmission based on FDDI (Fiber Distributed Data Interface) that uses shielded twisted-pair (STP) or unshielded twisted pair (UTP) copper wire instead of fiber optic lines.
• CDDI supports a dual-ring capacity of 200 Mbps. CDDI's maximum distance is up to 200 meters, which is much shorter than FDDI.
• CDDI is defined by the American National Standards Committee X3-T9.5 and conforms to the Open Systems Interconnection (OSI) model of functional layering. CDDI is officially named the Twisted-Pair Physical Medium Dependent (TP-PMD) standard and is also referred to as Twisted Pair Distributed Data Interface (TP-DDI).

 FDDI:

• Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium, although it was also later specified to use copper cable, in which case it may be called CDDI (Copper Distributed Data Interface).

• Preamble: 1 byte for synchronization.

• Start Delimiter: 1 byte that marks the beginning of the frame.

• Frame Control: 1 byte that specifies whether this is a data frame or control frame.

• Destination Address: 2-6 bytes that specifies address of destination station.

• Source Address: 2-6 bytes that specifies address of source station.

• Payload: A variable length field that carries the data from the network layer.

• Checksum: 4 bytes frame check sequence for error detection.

               End Delimiter: 1 byte that marks the end of the frame.

=>Communication Methods

The Internet Protocol and other network addressing systems

recognize five main addressing methodologies

• Anycast addressing routes datagrams to a single member of a

  group of potential receivers that are all identified by the same

  destination address. This is a one-to-nearest association.
• Broadcast addressing uses a one-to-many association,

  datagrams are routed from a single sender to multiple

  endpoints simultaneously in a single transmission. The network

  automatically replicates datagrams as needed for all network

  segments (links) that contain an eligible receiver.
• Multicast addressing uses a one-to-unique many association,

  datagrams are routed from a single sender to multiple selected

  endpoints simultaneously in a single transmission.
• Unicast addressing uses a one-to-one association between

  destination address and network endpoint: each destination

  address uniquely identifies a single receiver endpoint.
• Geocast refers to the delivery of information to a group of

  destinations in a network identified by their geographical

  locations. It is a specialized form of Multicast addressing used

  by some routing protocols for mobile ad hoc networks.

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TCP/IP model

The TCP/IP model was developed prior to the OSI model. The TCP/IP model is not exactly similar to the OSI model. TCP/IP model, it was designed and developed by Department of Defense (DoD) in 1960s and is based on standard protocols.

Network Access Layer

• A network layer is the lowest layer of the TCP/IP model.
• A network layer is the combination of the Physical layer and Data Link layer defined in the OSI reference model.
• It defines how the data should be sent physically through the network.
• This layer is mainly responsible for the transmission of the data between two devices on the same network.
• The functions carried out by this layer are encapsulating the IP datagram into frames transmitted by the network and mapping of IP addresses into physical addresses.
• The protocols used by this layer are ethernet, token ring, FDDI, X.25, frame relay.

Types of Transmission Media

Guided Media

• It is defined as the physical medium through which the signals are transmitted. It is also known as Bounded media.

Twisted pair:

• Twisted pair is a physical media made up of a pair of cables twisted with each other. A twisted pair cable is cheap as compared to other transmission media. Installation of the twisted pair cable is easy, and it is a lightweight cable. The frequency range for twisted pair cable is from 0 to 3.5KHz
• A twisted pair consists of two insulated copper wires arranged in a regular spiral pattern.
• The degree of reduction in noise interference is determined by the number of turns per foot. Increasing the number of turns per foot decreases noise interference.

Unshielded Twisted Pair:

An unshielded twisted pair is widely used in telecommunication. Following are the categories of the unshielded twisted pair cable:

• Category 1: Category 1 is used for telephone lines that have low-speed data.
• Category 2: It can support upto 4Mbps.
• Category 3: It can support upto 16Mbps.
• Category 4: It can support upto 20Mbps. Therefore, it can be used for long-distance communication.
• Category 5: It can support upto 200Mbps.

Advantages Of Unshielded Twisted Pair:

• It is cheap.
• Installation of the unshielded twisted pair is easy.
• It can be used for high-speed LAN.

Disadvantage:

• This cable can only be used for shorter distances because of attenuation.

Shielded Twisted Pair

A shielded twisted pair is a cable that contains the mesh surrounding the wire that allows the higher transmission rate.

Characteristics Of Shielded Twisted Pair:

• The cost of the shielded twisted pair cable is not very high and not very low.
• An installation of STP is easy.
• It has higher capacity as compared to unshielded twisted pair cable.
• It has a higher attenuation.
• It is shielded that provides the higher data transmission rate.

Disadvantages

• It is more expensive as compared to UTP and coaxial cable.
• It has a higher attenuation rate.

Crimping of Twisted pair cable:

Wire Cutter: - To cut the network cable of the required length from the bundle, you can use any standard wire cutter tool or can use a wire cutter tool that is specially designed for the twisted-pair cable. A twisted-pair wire cutter usually includes additional blades for stripping the wire.

Wire Stripper: - This tool is used to remove the outer and inner jackets of the network cable. Typically, you do not need to purchase this tool separately as all standard twisted-pair wire cutters are equipped with wire-strippers.

Crimp tool: - This tool is used to attach the connectors to the cable. Typically, this tool also includes a wire-cutter and wire-stripper. So if you have crimp tool, you don't have need to wire-cutter and wire-striper separately.

Coaxial Cable

• Coaxial cable is very commonly used transmission media, for example, TV wire is usually a coaxial cable.
• The name of the cable is coaxial as it contains two conductors parallel to each other.
• It has a higher frequency as compared to Twisted pair cable.
• The inner conductor of the coaxial cable is made up of copper, and the outer conductor is made up of copper mesh. The middle core is made up of non-conductive cover that separates the inner conductor from the outer conductor.
• The middle core is responsible for the data transferring whereas the copper mesh prevents from the EMI(Electromagnetic interference).

Coaxial cable is of two types:

1. Baseband transmission: It is defined as the process of transmitting a single signal at high speed.
2. Broadband transmission: It is defined as the process of transmitting multiple signals simultaneously.

Advantages Of Coaxial cable:

• The data can be transmitted at high speed.
• It has better shielding as compared to twisted pair cable.
• It provides higher bandwidth.

Disadvantages Of Coaxial cable:

• It is more expensive as compared to twisted pair cable.
• If any fault occurs in the cable causes the failure in the entire network.

Fibre Optic

• Fibre optic cable is a cable that uses electrical signals for communication.
• Fibre optic is a cable that holds the optical fibres coated in plastic that are used to send the data by pulses of light.
• The plastic coating protects the optical fibres from heat, cold, electromagnetic interference from other types of wiring.
• Fibre optics provide faster data transmission than copper wires.

Diagrammatic representation of fibre optic cable:

Basic elements of Fibre optic cable:

• Core: The optical fibre consists of a narrow strand of glass or plastic known as a core. A core is a light transmission area of the fibre. The more the area of the core, the more light will be transmitted into the fibre.
• Cladding: The concentric layer of glass is known as cladding. The main functionality of the cladding is to provide the lower refractive index at the core interface as to cause the reflection within the core so that the light waves are transmitted through the fibre.
• Jacket: The protective coating consisting of plastic is known as a jacket. The main purpose of a jacket is to preserve the fibre strength, absorb shock and extra fibre protection.

Following are the advantages of fibre optic cable over copper:

• Greater Bandwidth: The fibre optic cable provides more bandwidth as compared copper. Therefore, the fibre optic carries more data as compared to copper cable.
• Faster speed: Fibre optic cable carries the data in the form of light. This allows the fibre optic cable to carry the signals at a higher speed.
• Longer distances: The fibre optic cable carries the data at a longer distance as compared to copper cable.
• Better reliability: The fibre optic cable is more reliable than the copper cable as it is immune to any temperature changes while it can cause obstruct in the connectivity of copper cable.
• Thinner and Sturdier: Fibre optic cable is thinner and lighter in weight so it can withstand more pull pressure than copper cable.

UnGuided Transmission

• An unguided transmission transmits the electromagnetic waves without using any physical medium. Therefore it is also known as wireless transmission.
• In unguided media, air is the media through which the electromagnetic energy can flow easily.

Unguided transmission is broadly classified into three categories:

Radio waves

• Radio waves are the electromagnetic waves that are transmitted in all the directions of free space.
• Radio waves are omnidirectional, i.e., the signals are propagated in all the directions.
• The range in frequencies of radio waves is from 3Khz to 1 khz.
• In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the wave sent by the sending antenna can be received by any receiving antenna.
• An example of the radio wave is FM radio.

Applications Of Radio waves:

• A Radio wave is useful for multicasting when there is one sender and many receivers.
• An FM radio, television, cordless phones are examples of a radio wave.

Advantages Of Radio transmission:

• Radio transmission is mainly used for wide area networks and mobile cellular phones.
• Radio waves cover a large area, and they can penetrate the walls.
• Radio transmission provides a higher transmission rate.

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Microwaves

Microwaves are of two types:

• Terrestrial microwave
• Satellite microwave communication.

Terrestrial Microwave Transmission

• Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio signal from one ground-based microwave transmission antenna to another.
• Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000 GHz.
• Microwaves are unidirectional as the sending and receiving antenna is to be aligned, i.e., the waves sent by the sending antenna are narrowly focussed.
• In this case, antennas are mounted on the towers to send a beam to another antenna which is km away.
• It works on the line of sight transmission, i.e., the antennas mounted on the towers are the direct sight of each other.

Characteristics of Microwave:

• Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz to 21-23 GHz.
• Bandwidth: It supports the bandwidth from 1 to 10 Mbps.
• Short distance: It is inexpensive for short distance.
• Long distance: It is expensive as it requires a higher tower for a longer distance.
• Attenuation: Attenuation means loss of signal. It is affected by environmental conditions and antenna size.

Advantages Of Microwave:

• Microwave transmission is cheaper than using cables.
• It is free from land acquisition as it does not require any land for the installation of cables.
• Microwave transmission provides an easy communication in terrains as the installation of cable in terrain is quite a difficult task.
• Communication over oceans can be achieved by using microwave transmission.

Disadvantages of Microwave transmission:

• Eavesdropping: An eavesdropping creates insecure communication. Any malicious user can catch the signal in the air by using its own antenna.
• Out of phase signal: A signal can be moved out of phase by using microwave transmission.
• Susceptible to weather condition: A microwave transmission is susceptible to weather condition. This means that any environmental change such as rain, wind can distort the signal.
• Bandwidth limited: Allocation of bandwidth is limited in the case of microwave transmission.

Satellite Microwave Communication

• A satellite is a physical object that revolves around the earth at a known height.
• Satellite communication is more reliable nowadays as it offers more flexibility than cable and fibre optic systems.
• We can communicate with any point on the globe by using satellite communication.

How Does Satellite work?

The satellite accepts the signal that is transmitted from the earth station, and it amplifies the signal. The amplified signal is retransmitted to another earth station.

Advantages Of Satellite Microwave Communication:

• The coverage area of a satellite microwave is more than the terrestrial microwave.
• The transmission cost of the satellite is independent of the distance from the centre of the coverage area.
• Satellite communication is used in mobile and wireless communication applications.
• It is easy to install.
• It is used in a wide variety of applications such as weather forecasting, radio/TV signal broadcasting, mobile communication, etc.

Disadvantages Of Satellite Microwave Communication:

• Satellite designing and development requires more time and higher cost.
• The Satellite needs to be monitored and controlled on regular periods so that it remains in orbit.
• The life of the satellite is about 12-15 years. Due to this reason, another launch of the satellite has to be planned before it becomes non-functional.

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Infrared

• An infrared transmission is a wireless technology used for communication over short ranges.
• The frequency of the infrared in the range from 300 GHz to 400 THz.
• It is used for short-range communication such as data transfer between two cell phones, TV remote operation, data transfer between a computer and cell phone resides in the same closed area.

Characteristics Of Infrared:

• It supports high bandwidth, and hence the data rate will be very high.
• Infrared waves cannot penetrate the walls. Therefore, the infrared communication in one room cannot be interrupted by the nearby rooms.
• An infrared communication provides better security with minimum interference.
• Infrared communication is unreliable outside the building because the sun rays will interfere with the infrared waves.

Multiplexing:

Multiplexing is a technique used to combine and send the multiple data streams over a single medium. The process of combining the data streams is known as multiplexing and hardware used for multiplexing is known as a multiplexer.

Multiplexing is achieved by using a device called Multiplexer (MUX) that combines n input lines to generate a single output line. Multiplexing follows many-to-one, i.e., n input lines and one output line.

Demultiplexing:

Demultiplexing is achieved by using a device called Demultiplexer (DEMUX) available at the receiving end. DEMUX separates a signal into its component signals (one input and n outputs). Therefore, we can say that demultiplexing follows the one-to-many approach.

UNIT - 2

What is a packet?

In networking, a packet is a small segment of a larger message. Data sent over computer networks*, such as the Internet, is divided into packets. These packets are then recombined by the computer or device that receives them.

What is a protocol?

A network protocol is an established set of rules that determine how data is transmitted between different devices in the same network.

1. Transmission Control Protocol (TCP)
2. Internet Protocol (IP)
3. User Datagram Protocol (UDP)
4. Post office Protocol (POP)
5. Simple mail transport Protocol (SMTP)
6. File Transfer Protocol (FTP)
7. Hyper Text Transfer Protocol (HTTP)
8. Hyper Text Transfer Protocol Secure (HTTPS)
9. Telnet
10. Gopher
11. ARP (Address Resolution Protocol)
12. DHCP (Dynamic Host Configuration Protocol)
13. IMAP4 (Internet Message Access Protocol)
14. SIP (Session Initiation Protocol)
15. RTP (Real-Time Transport Protocol)
16. RLP (Resource Location Protocol)
17. RAP (Route Access Protocol)
18. L2TP (Layer Two Tunnelling Protocol)
19. PPTP (Point To Point Tunnelling Protocol)
20. SNMP (Simple Network Management Protocol)
21. TFTP (Trivial File Transfer Protocol)

TCP

TCP stands for Transmission Control Protocol. It is a transport layer protocol that facilitates the transmission of packets from source to destination. It is a connection-oriented protocol. The main functionality of the TCP is to take the data from the application layer. Then it divides  the data into a several packets, provides numbering to these packets, and finally transmits these  packets to the destination. Features of TCP protocol Transport Layer Protocol TCP is a transport layer protocol as it is used in transmitting the data from the sender to the receiver. Reliable TCP is a reliable protocol as it follows the flow and error control mechanism. Full duplex It is a full-duplex means that the data can transfer in both directions at the same time. Order of the data is maintained Connection-oriented Stream-oriented Advantages of TCP It provides a connection-oriented reliable service, which means that it guarantees the delivery  of data packets. If the data packet is lost across the network, then the TCP will resend the lost packets. It provides a flow control mechanism using a sliding window protocol. It provides error detection by using checksum and error control by using Go Back or ARP protocol. It eliminates the congestion by using a network congestion avoidance algorithm that includes  various schemes such as additive increase/multiplicative decrease (AIMD), slow start, and  congestion window. Disadvantage of TCP It increases a large amount of overhead as each segment gets its own TCP header, so fragmentation  by the router increases the overhead.

 

UDP

 UDP stands for User Datagram Protocol. 

 The David P. Reed developed the UDP protocol in 1980

.

User Datagram Protocol (UDP) is a Transport Layer protocol. UDP is a part of Internet Protocol suite, referred as UDP/IP suite. Unlike TCP, it is unreliable and connectionless protocol. So, there is no need to establish connection prior to data transfer. 

Features of UDP protocol The following are the features of the UDP protocol: Transport layer protocol UDP is the simplest transport layer communication protocol.  It contains a minimum amount of communication mechanisms.  Connectionless The UDP is a connectionless protocol as it does not create a virtual path to transfer the data. Ordered delivery of data is not guaranteed. In the case of UDP, the datagrams are sent in some order will be received in the same order is  not guaranteed as the datagrams are not numbered. Ports The UDP protocol uses different port numbers so that the data can be sent to the correct destination.  The port numbers are defined between 0 and 1023. Faster transmission UDP enables faster transmission as it is a connectionless protocol, i.e., no virtual path is required to transfer the data. Acknowledgment mechanism The UDP does have any acknowledgment mechanism, i.e., there is no handshaking between the UDP  sender and UDP receiver. Stateless It is a stateless protocol that means that the sender does not get the acknowledgement for the packet which has been sent. Limitations It provides an unreliable connection delivery service. It does not provide any services of IP  except that it provides process-to-process communication. The UDP message can be lost, delayed, duplicated, or can be out of order. It does not provide a reliable transport delivery service. It does not provide any acknowledgment  or flow control mechanism. However, it does provide error control to some extent. Advantages It produces a minimal number of overheads. A Router is a process of selecting path along which the data can be transferred from source to  the destination. Routing is performed by a special device known as a router. A Router works at the network layer in the OSI model and internet layer in TCP/IP model A router is a networking device that forwards the packet based on the information available  in the packet header and forwarding table. The routing algorithms are used for routing the packets. The routing algorithm is nothing but  a software responsible for deciding the optimal path through which packet can be transmitted. The routing protocols use the metric to determine the best path for the packet delivery.  The metric is the standard of measurement such as hop count, bandwidth, delay, current load on the path, etc. used by the routing algorithm to determine the optimal path to the destination. The routing algorithm initializes and maintains the routing table for the process of path  determination. Types of Routing Static Routing Static Routing is also known as Nonadaptive Routing. It is a technique in which the administrator manually adds the routes in a routing table. A Router can send the packets for the destination along the route defined by the administrator. In this technique, routing decisions are not made based on the condition or topology of the networks Advantages Of Static Routing Following are the advantages of Static Routing: No Overhead: It has ho overhead on the CPU usage of the router. Therefore, the cheaper router can be used to obtain static routing. Bandwidth: It has not bandwidth usage between the routers. Security: It provides security as the system administrator is allowed only to have control over the routing to a particular network. Disadvantages of Static Routing: Following are the disadvantages of Static Routing: For a large network, it becomes a very difficult task to add each route manually to the routing table. The system administrator should have a good knowledge of a topology as he has to add each route manually. Default Routing Default Routing is a technique in which a router is configured to send all the packets to the same hop device, and it doesn't matter whether it belongs to a particular network or not. A Packet is transmitted to the device for which it is configured in default routing. Default Routing is used when networks deal with the single exit point. It is also useful when the bulk of transmission networks have to transmit the data to the same hp device. When a specific route is mentioned in the routing table, the router will choose the specific route rather than the default route. The default route is chosen only when a specific route is not mentioned in the routing table. Dynamic Routing It is also known as Adaptive Routing. It is a technique in which a router adds a new route in the routing table for each packet in response to the changes in the condition or topology of the network. Dynamic protocols are used to discover the new routes to reach the destination. In Dynamic Routing, RIP and OSPF are the protocols used to discover the new routes. If any route goes down, then the automatic adjustment will be made to reach the destination. The Dynamic protocol should have the following features: All the routers must have the same dynamic routing protocol in order to exchange the routes. If the router discovers any change in the condition or topology, then router broadcast this information to all other routers. Advantages of Dynamic Routing: It is easier to configure. It is more effective in selecting the best route in response to the changes in the condition or topology. Disadvantages of Dynamic Routing: It is more expensive in terms of CPU and bandwidth usage. It is less secure as compared to default and static routing. What is IP? Here, IP stands for internet protocol. It is a protocol defined in the TCP/IP model used for sending the packets from source to destination. The main task of IP is to deliver the packets from source to the destination based on the IP addresses available in the packet headers. IP defines the packet structure that hides the data which is to be delivered as well as the addressing method that labels the datagram with a source and destination information. An IP protocol provides the connectionless service, which is accompanied by two transport protocols, i.e., TCP/IP and UDP/IP, so internet protocol is also known as TCP/IP or UDP/IP. The first version of IP (Internet Protocol) was IPv4. After IPv4, IPv6 came into the market, which has been increasingly used on the public internet since 2006. DHCP  DHCP stands for dynamic host configuration protocol and is a network protocol used on IP networks where a DHCP server automatically assigns an IP address and other information to each host on the network so they can communicate efficiently with other endpoints. In addition to the IP address, DHCP also assigns the subnet mask, default gateway address, domain name server (DNS) address and other pertinent configuration parameters. Request for comments (RFC) 2131 and 2132 define DHCP as an Internet Engineering Task Force (IETF)- defined standard based on the BOOTP protocol. Static IP address: A static IP address is simply an address that doesn't change. Once your device is assigned a static IP address, that number typically stays the same until the device is decommissioned or your network architecture changes. Static IP addresses generally are used by servers or other important equipment. Static IP addresses are assigned by Internet Service Providers (ISPs). Your ISP may or may not allocate you a static IP address depending on the nature of your service agreement. We describe your options a little later, but for now assume that a static IP address adds to the cost of your ISP contract. Advantages of a static IP Better DNS support Server hosting Convenient remote access More reliable communication More reliable geo-location services Disadvantages of a static IP Static IPs are more hackable Higher cost Real-world security concerns Dynamic IP address Dynamic IP addresses are subject to change, sometimes at a moment's notice. Dynamic addresses are assigned, as needed, by Dynamic Host Configuration Protocol (DHCP) servers. We use dynamic addresses because IPv4 doesn't provide enough static IP addresses to go around. So, for example, a hotel probably has a static IP address, but each individual device within its rooms would have a dynamic IP address. On the internet, your home or office may be assigned a dynamic IP address by your ISP's DHCP server. Within your home or business network, the dynamic IP address for your devices -- whether they are personal computers, smartphones, streaming media devices, tablet, what have you -- are probably assigned by your network router. Dynamic IP is the standard used by and for consumer equipment. Advantages of a dynamic IP Easy, automatic configuration Lower fees Unlimited IP addressing Potentially better security Better physical security Disadvantages of a dynamic IP Unlikely to work well for hosted services May limit remote access Potentially more downtime Less accurate geolocation Types of IP Addresses: Public IP Addresses A public IP address is an address where one primary address is associated with your whole network. In this type of IP address, each of the connected devices has the same IP address. This type of public IP address is provided to your router by your ISP. Private IP Addresses A private IP address is a unique IP number assigned to every device that connects to your home internet network, which includes devices like computers, tablets, smartphones, which is used in your household. It also likely includes all types of Bluetooth devices you use, like printers or printers, smart devices like TV, etc. With a rising industry of internet of things (IoT) products, the number of private IP addresses you are likely to have in your own home is growing. What  is  IP Address  ? An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address serves two main functions: Host or network interface identification and location addressing 1. IP version 4 : The number of networks and the number of hosts per class can be derived by this formula − An IPv4 address has a size of 32 bits. which limits the address space to 4294967296 (232) addresses. some addresses are reserved for special purposes such as private networks (~18 million addresses) and multicast addressing (~270 million addresses). IPv4 addresses are usually represented in dot-decimal notation. IP address is divide into four section. Each ranging from 0 to 255, separated by dots. e.g., 172.16.254.1. Each part represents a group of 8 bits (an octet) of the address.  In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations. Class Leading bits Size of network number bit field Number of networks Number of addresses per network Start address End address A 0 8 128 (27) 16777216 (224) 0.0.0.0 127.255.255.255 B 10 16 16384 (214) 65536 (216) 128.0.0.0 191.255.255.255 C 110 24 2097152 (221) 256 (28) 192.0.0.0 223.255.255.255 Class A Address The first bit of the first octet is always set to 0 (zero). Thus the first octet ranges from 1 – 127, i.e. Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only. The IP range 127.x.x.x is reserved for loopback IP addresses. The default subnet mask for Class A IP address is 255.0.0.0 which implies that Class A addressing can have 126 networks (27-2) and 16777214 hosts (224-2). Class A IP address format is thus: 0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH Class B Address An IP address which belongs to class B has the first two bits in the first octet set to 10, i.e. Class B IP Addresses range from 128.0.x.x to 191.255.x.x. The default subnet mask for Class B is 255.255.x.x. Class B has 16384 (214) Network addresses and 65534 (216-2) Host addresses. Class B IP address format is: 10NNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH Class C Address The first octet of Class C IP address has its first 3 bits set to 110, that is − Class C IP addresses range from 192.0.0.x to 223.255.255.x. The default subnet mask for Class C is 255.255.255.x. Class C gives 2097152 (221) Network addresses and 254 (28-2) Host addresses. Class C IP address format is: 110NNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH Class D Address Very first four bits of the first octet in Class D IP addresses are set to 1110, giving a range of − Class D has IP address range from 224.0.0.0 to 239.255.255.255. Class D is reserved for Multicasting. In multicasting data is not destined for a particular host, that is why there is no need to extract host address from the IP address, and Class D does not have any subnet mask. Class E Address This IP Class is reserved for experimental purposes only for R&D or Study. IP addresses in this class ranges from 240.0.0.0 to 255.255.255.254. Like Class D, this class too is not equipped with any subnet mask.