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MEDIA

1. Transmission Media The means through which data is transmitted from one place to another is called transmission or communication media. There are two categories of transmission media used in computer communications.

1- Bounded/guided media
2- Unbounded/unguided media

(a). Bounded Media Bounded media are the physical links through which signals are confined to narrow path. These are also called guide media. Bounded media are made up of a external conductor (Usually Copper) bounded by jacket material. Bounded media are great for LABS because they offer high speed, good security and low cast. However, some time they cannot be used due distance communication. Three common types of bounded media are used of the data transmission. These are

1- Twisted Pairs Cable
2- Coaxial Cable
3- Fiber Optics Cable

2. Twisted Pair Cable

The most popular network cabling is Twisted pair. It is light weight, easy to install, inexpensive and support many different types of network. It also supports the speed of 100 mbps. Twisted pair cabling is made of pairs of solid or stranded copper twisted along each other. The twists are done to reduce vulnerability to EMI and cross talk. The number of pairs in the cable depends on the type. There are two types of twisted pairs cable.

1- Unshielded twisted pair (UTP)
2- Shielded twisted pair (STP)

(a) Unshielded twisted pair (UTP)

(aa) UTP is more common. It can be either voice grade or data grade depending on the condition. UTP cable normally has an impedance of 100 ohm. UTP cost less than STP and is easily available due to its many use.

(ab) UTP cables are generally used to construct an Ethernet network in a star arrangement. UTP connectors are called RJ-45 connector. UTP cable comes in various grades called Categories for example CAT 1, 2, 3, 4, 5& CAT 6 etc.

　

　

　

　

Categories of Unshielded Twisted Pair

Category	Speed	Use
1	1 Mbps	Voice Only (Telephone Wire)
2	4 Mbps	Local Talk & Telephone (Rarely used)
3	16 Mbps	10BaseT Ethernet
4	20 Mbps	Token Ring (Rarely used)
5	100 Mbps (2 pair)	100BaseT Ethernet
5	1000 Mbps (4 pair)	Gigabit Ethernet
5e	1,000 Mbps	Gigabit Ethernet
6	10,000 Mbps	Gigabit Ethernet

Characteristics of UTP

1- High speed capacity.
2- High attenuation.
3- Affected to EMI.
4- 100 meter distance limit.
Disadvantages of UTP

Short distance due to attenuation

(b). Shielded twisted pair (STP) It is similar to UTP but has a mesh shielding that’s protects it from EMI which allows for higher transmission rate. In STP, an extra layer of metal foil present between the twisted pairs of copper wires and the outer sheath. The purpose of this layer is to provide additional protection from EMI and RFI. However, this shielding reflects back the normal radiation emitted by the wires. This radiation may interfere with signal transmitted by the cable. To prevent this reflection a coating of dielectric insulator which absorbs the radiation is provided on the internal surface of the metal foil.

　
　
　

　

　

　

　

　

　

　

　

Characteristics of STP
1- Higher capacity than UTP
2- Higher attenuation, but same as UTP
3- Medium immunity from EMI
4- 100 meter limit

3. UTP Connectors RJ45 (Registered Jack 45) is a standard type of connector for network cables. RJ45 connectors have eight pins to which the wire strands of a cable are connected.

(a) Colour coding of UTP cable

RJ 45 Pin NO

Pin 1

Pin 2

Pin 3

Pin 4

Pin 5

Pin 6

Pin 7

Pin 8

Colour coding

White/orange

Orange

White/green

Blue

White/blue

Green

White/brown

Brown

There are two types of UTP cable wires connections-

1- Straight through cables

2- Crossover Cables.

Straight-through cable means that wire 1 coming in connects to wire 1, going out wire 2 connects to wire 2 and so on.

Straight Cable Connection
RJ-45 Pin	Colour coding of UTP wires	Function	RJ-45 Pin	Colour coding of UTP wires	Function
1	White Orange	Tx+	1	White Orange	Rx+
2	Orange	Tx-	2	Orange	Rx-
3	White Green	Rx+	3	White Green	Tx+
4	blue	Not used	4	blue	Not used
5	White Blue	Not used	5	White Blue	Not used
6	Green	Rx-	6	Green	Tx-
7	White Brown	Not used	7	White Brown	Not used
8	Brown	Not used	8	Brown	Not used

A crossover cable directly connects two network devices of the same type to each other over Ethernet.

Cross Cable connection
Switch A side			Switch B side
RJ-45 Pin	Colour coding of UTP wires	Function	RJ-45 Pin	Colour coding of UTP wires	Function
1	White Orange	Tx+	1	White Green	Tx+
2	Orange	Tx-	2	Green	Tx-
3	White Green	Rx+	3	White Orange	Rx+
4	blue	Not used	4	blue	Not used
5	White Blue	Not used	5	White Blue	Not used
6	Green	Rx-	6	Orange	Rx-
7	White Brown	Not used	7	White Brown	Not used
8	Brown	Not used	8	Brown	Not used

4. Coaxial Cable

Coaxial cable is very common & widely used communication media. e.g. TV wire is usually coaxial.

Coaxial cable gets its name because it contains two conductors that are parallel to each other. The centres conductor in the cable is usually copper. The copper can be either a solid wire or stranded martial.

Outside this central Conductor is a non-conductive material. The other Conductor is a fine mesh made from Copper. It is used to help shield the cable form EMI.

There are two types of coaxial cable-

1- Thin coaxial cable

2- Thick coaxial cable

Characteristics Of Coaxial Cable

1- Up to 10Mbps capacity.
2- Medium immunity from EMI.
3- Medium attenuation.

　
　
Connector of coaxial cable

　

　

5. Fiber Optics Fiber optic cable uses electrical signals to transmit data. In fiber optic cable light moves in one direction, for two way communication to take place a second connection must be made between the two devices. It is actually two stands of cable. Each stand is responsible for one direction of communication. A laser at one device sends pulse of light through this cable to other device. These pulses translated into "1’s" and "0’s" at the other end.

In the center of fiber cable is a glass stand or core. The light from the laser moves through this glass to the other device around the internal core is a reflective material known as CLADDING. No light escapes the glass core because of this reflective cladding. Fiber optic cable has bandwidth more than 2 Gbps (Gigabytes per Second)

Characteristics Of Fiber Optic Cable

1- Capable of extremely high speed
2- Extremely low attenuation
3- No EMI interference

　
　
　
　
　

Connectors

6. Fiber Optic Cable Connectors

(a) SC Connector A fiber-optic cable connector that uses a push-pull latching mechanism similar to common audio and video cables. For bi-directional transmission, two fiber cables and two SC connectors (Dual SC) are generally used.

(b) ST Connector A fiber-optic cable connector that uses a half-twist bayonet type of lock to keep the connection secure. For bi-directional transmission, two fiber cables and two ST connectors are generally used.

(c) MTRJ The MTRJ connector is a small form-factor fiber optic connector which resembles the RJ-45 connector used in Ethernet networks.

(d) FC The FC connector is a fiber-optic connector with a threaded body, which was designed for use in high-vibration environments. It is commonly used with single-mode optical fiber. FC connectors are used in data com, telecommunications, measurement equipment, and single-mode lasers. They are becoming less common, displaced by SC and LC connectors.

　

　

　

　

　

7. Media Type Comparison

Media Type	Maximum Segment Length	Speed	Cost	Advantages	Disadvantages
UTP	100 m	10 Mbps to 1000 Mbps	Least expensive	Easy to install; widely available and widely used	Susceptible to interference; can cover only a limited distance
STP	100 m	10 Mbps to 100 Mbps	More expensive than UTP	Reduced crosstalk; more resistant to EMI than Thinnet or UTP	Difficult to work with; can cover only a limited distance
Coaxial	500 m (Thicknet) 185 m (Thinnet)	10 Mbps to 100 Mbps	Relatively inexpensive, but more costly than UTP	Less susceptible to EMI interference than other types of copper media	Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network
Fiber-Optic	10 km and farther (single-mode) 2 km and farther (multimode)	100 Mbps to 100 Gbps (single mode) 100 Mbps to 9.92 Gbps (multimode)	Expensive	Cannot be tapped, so security is better; can be used over great distances; is not susceptible to EMI; has a higher data rate than coaxial and twisted-pair cable	Difficult to terminate

8. Wireless media Wireless communication uses radio frequencies (RF) or infrared (IR) waves to transmit data between devices on a LAN. For wireless LANs, a key component is the wireless hub, or access point, used for signal distribution

To receive the signals from the access point, a PC or laptop must install a wireless adapter card (wireless NIC).

No physical medium is necessary for wireless signals, making them a very versatile way to build a network. Wireless signals use portions of the RF spectrum to transmit voice, video, and data.

Wireless frequencies range from 3 kilohertz (kHz) to 300 gigahertz (GHz). The data-transmission rates range from 9 kilobits per second (kbps) to as high as 54 Mbps.

Low-frequency electromagnetic waves have a long wavelength while high-frequency electromagnetic waves have a short wavelength.

　

　

　

　

Applications of wireless comn

1- Accessing the Internet using a cellular phone

2- Establishing a home or business Internet connection over satellite

3- Beaming data between two hand-held computing devices

4- Using a wireless projectors, keyboard and mouse for the PC

5- Another application of wireless data communication is the wireless LAN (WLAN), IEEE 802.11 standards. WLANs typically use radio waves ( 902 megahertz ), microwaves ( 2.4 GHz), and IR waves ( 820 nanometers) for communication.

LAN

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1. Ethernet The IEEE has standardized a number of LAN and MAN under the name of IEEE 802. Ethernet is the most popular lower-layer protocol used in LANs. There have been several enhancements to the original version of Ethernet, and the current versions support network transmission speeds ranging from 10 Mbps to 1,000 Mbps.

Ethernet uses a technique called the Carrier Sense Multiple Access/Collision Detection (CSMA/CD), also known as IEEE 802.3 to provide media access to devices on the network. A carrier is a signal containing some specific data. CSMA/CD works in the following manner.

(a) The device that needs to send data checks the cable for any signals. This is called Carrier Sense.

(b) If no carrier is found, the device accesses the medium and transmits data signals, but it is possible that multiple devices start transmitting signals simultaneously. This is called Multiple Access.

(c) When multiple devices transmit signals simultaneously, a collision occurs. The device nearest to the point of collision detects the collision and informs all the devices about the collision, which is called Collision Detection. The devices then wait for a random period of time before retransmitting the data.

2. Ethernet Cabling

Name	Cable	Max.seg	Nodes/seg	Advantages
10Base5	Thick coax	500m	100	Original cable; now obsolete
10Base2	Thin coax	185m	30	No hub needed
10Base-T	Twisted pair	100m	1024	Cheapest system
10Base-F	Fiber optics	2000m	1024	Best between building

The common names for various types of Ethernet are interpreted based on the following format:

Some types of Ethernet cables

(a) 10 Base-T 10Base-T means that the cable has a data rate of 10Mbps, uses baseband, and perform data transmission using twisted-pair cable. The maximum length of a 10Base-T segment is 100 meters. Repeaters can be used to extend the maximum cable length. The minimum cable length between computers is about 8 feet. A 10BaseT LAN can support up to 1024 computers. 10BaseT solution provides the advantages of a star-wired topology. The 5-4-3 rule for Ethernet states that an Ethernet can have a maximum of five segments with a maximum of four repeaters, and out of the five segments only three segments can have nodes attached to them.

(b) 10Base2 10Base2 means that the cable has a data rate of 10 Mbps, uses base band transmission, and has a maximum cable length of 185 meters per segment, each of which can handle only 30 machines. The minimum distance between two nodes in this type of Ethernet is 16.5 feet.

(c) 10Base5 10Base5 popularly called thick Ethernet means that the cable has data rate of 10 Mbps, uses baseband transmission, and has a maximum cable length of approximately upto 500 meters. It can support a maximum of 100 computers in a given segment. Thus, 300 nodes can be connected in an Ethernet network implemented using thickest cables. In addition, the minimum distance between two nodes should be 8.25 feet.

(d) 10BaseF The 10BaseF which uses Fiber optics. This alternative is expensive due to the cost of the connectors and terminators, but it has excellent noise immunity. It offers good security since wire tapping Fiber is much more difficult than wire tapping copper wire. It allows a maximum distance of 1.3 mile per segment. You can connect up to 1024 nodes on such a network.

(e) 100BaseX (Fast Ethernet) The Fast Ethernet standard supports speed of 100Mbps and uses the same frame formats as the 10 Mbps Ethernet. The 100 denotes 100 Mbps data speed. There are three categories in 100BaseX Ethernet: 100BaseT4, 100BaseTX, and 100BaseFX. The 100baseT4 uses category 3, 4, or 5 UTP cable. The 100BaseTX Ethernet uses category 5 STP or UTP cable and 100BaseFX uses fiber optic cable. The distance between a computer and a hub con not be greater than 330 feet. The 5-4-3 rule is not applicable to fast Ethernet. Fast Ethernet is the most popular Ethernet because of high speed and cost-effectiveness.

(f) 1000BaseT IEEE 802.ab describes Gigabit Ethernet using Cat-5e cables. These networks can transfer data at 1 Gbps rate.

IP ADDRESSING

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1. IPv4 Every machine on the network has a unique identifying number, called an IP Address. It is a 32 bit addressing scheme to identify the devices on a network. To make it easier for us to remember, IP addresses are normally expressed in decimal format as a "dotted decimal number" (four decimal numbers separated by dots). A typical IP address looks like this -

216.27.61.137

But computers communicate address in binary form. Look at the same IP address in 32 bit binary format:-

11011000.00011011.00111101.10001001

The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers.

The octets are divided into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses.

2. Classes: There are 5 classes of IP addresses .These are as under:-

(a) Class A This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class. The other three octets are used to identify each host. This means that there are 126 Class A networks each with 16,777,214 (2^{24 -2) possible hosts for a total of 2,147,483,648 (231) unique IP addresses. Class A networks account for half of the total available IP addresses. In Class A networks, the high order bit value (the very first binary number) in the first octet is always 0.}

Loopback - The IP address 127.0.0.1 is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing.

(b) Class B Class B is used for medium-sized networks. IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host.

This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses. Class B networks make up a quarter of the total available IP addresses. Class B networks have a first bit value of 1 and a second bit value of 0 in the first octet.

(c) Class C Class C addresses are commonly used for small to mid-size Organizations. IP addresses with a first octet from 192 to 223 are part of this class. Class C addresses also include the second and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (221) Class C networks each with 254 (28 -2) possible hosts for a total of 536,870,912 (229) unique IP addresses. Class C networks make up an eighth of the total available IP addresses. Class C networks have a first bit value of 1, second bit value of 1 and a third bit value of 0 in the first octet.

(d) Class D Used for multicasts, Class D is slightly different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 0. The other 28 bits are used to identify the group of computers the multicast message is intended for.

(e) Class E Class E is used for experimental purposes only. Like Class D, it is different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 1. The other 28 bits are used to identify the group of computers the multicast message is intended for.

3. Features of IP Address Classes:

IP add class	IP address range	Example	No of NW supports	NO of hosts supports	Application
Class A	^{1.0.0.0 to 127.255.255.255 (127.0.0.1 reserved for loopback)}	^124.12.20.6	¹²⁶	^16,777,216	Used in very large organizations with more than 65536 computers on a network and large ISPs.
Class B	^{128.0.0.0 to 191}	^168.154.12.3	¹⁶³⁸⁴	^65,536	Used for more than 256 and fewer than 65536 computers on a network.
Class C	^{192.0.0.0 to 223.255.255.255}	^{198.168.154.32}	^2097152	²⁵⁶	Most commonly used IP address classes in LANs.
Class D	^{224.0.0.0 to 239.255.255.255}	^{225.255.251.124}	^{Not applicable}	^{Not applicable}	Multicasts
Class E	^{240.0.0.0 to 255.255.255.255}	^{242.103.26.125}	^{Not applicable}	^{Not applicable}	Experimental purpose

4. IPv6 address

An Internet Protocol Version 6 address (IPv6 address) is a numerical label that is used to identify a network interface of a computer or other network node participating in an IPv6-enabled computer network.

IP addresses serve the purpose of uniquely identifying the individual network interface(s) of a host, locating it on the network, and thus permitting the routing of IP packets between hosts.

IPv6 is the successor to the Internet's first addressing infrastructure, Internet Protocol version 4 (IPv4). In contrast to IPv4, which defined an IP address as a 32-bit number, IPv6 addresses have a size of 128 bits. Therefore, IPv6 has a vastly enlarged address space compared to IPv4.

5. Difference between IPv4 and IPv6

IPv4	IPv6
a) ) It has a larger address space.	a) IPv6 has a fixed length header
b) IPv4 uses 4 bytes	b) IPv6 uses 16 bytes.
c) IPv4 can support up to 232 addresses.	c) IPv6 support up to 2128 addresses
d) IPv4 uses 4 bytes	d) IPv6 uses 16 bytes.
e) IPv4 is 32 bits IP address.	e) Address extended to 128 bits.
	f) Enhanced Security and QoS Features

6. Subnetting

1- A subnet is a segment of a network. Subnetting is a technique that allows a network administrator to divide one physical network into smaller logical networks and, thus, control the flow of traffic for security or efficiency reasons.

2- Dividing a network into several subnets can serve a number of purposes to reduce network traffic by decreasing the number of broadcasts to exceed the limitations in a local area network, for instance the maximum number of allowed hosts.

3- Subnets are created by using a so-called subnet mask to divide a single Class A, B, or C network number into smaller pieces. Subnets can again be subnetted into sub-subnets.

How does subnetting work?

An IP address consists of a network portion and a host portion. A subnet is created by borrowing bits from the part of the IP address which normally designates the Host And using them to designate one or smaller, secondary networks (subnets) within the original network. The network prefix and subnet number in combination are called the extended network prefix.

Subnet Mask A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and Host Address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. Within a given network, two Host Addresses are reserved for special purpose. The "0" address is assigned a network address and "255" is assigned to a broadcast address, and they cannot be assigned to a host. Examples of commonly used subnet masks for classed networks are 8-bits (Class A), 16-bits (Class B) and 24-bits (Class C), and classless (CIDR) networks are as follows:-

CIDR	/4	240,435,456	11110000 00000000 00000000 00000000	240.0.0.0
CIDR	/5	134,217,728	11111000 00000000 00000000 00000000	248.0.0.0
CIDR	/6	67,108,864	11111100 00000000 00000000 00000000	252.0.0.0
CIDR	/7	33,554,432	11111110 00000000 00000000 00000000	254.0.0.0
A	/8	16,777,216	11111111 00000000 00000000 00000000	255.0.0.0
CIDR	/9	8,388,608	11111111 10000000 00000000 00000000	255.128.0.0
CIDR	/10	4,194,304	11111111 11000000 00000000 00000000	255.192.0.0
CIDR	/11	2,097,152	11111111 11100000 00000000 00000000	255.224.0.0
CIDR	/12	1,048,576	11111111 11110000 00000000 00000000	255.240.0.0
CIDR	/13	524,288	11111111 11111000 00000000 00000000	255.248.0.0
CIDR	/14	262,144	11111111 11111100 00000000 00000000	255.252.0.0
CIDR	/15	131,072	11111111 11111110 00000000 00000000	255.254.0.0
CIDR	/16	65,534	11111111 11111111 00000000 00000000	255.255.0.0
CIDR	/17	32,768	11111111 11111111 10000000 00000000	255.255.128.0
CIDR	/18	16,384	11111111 11111111 11000000 00000000	255.255.192.0
CIDR	/19	8,192	11111111 11111111 11100000 00000000	255.255.224.0
CIDR	/20	4,096	11111111 11111111 11110000 00000000	255.255.240.0
CIDR	/21	2,048	11111111 11111111 11111000 00000000	255.255.248.0
CIDR	/22	1,024	11111111 11111111 11111100 00000000	255.255.252.0
CIDR	/23	512	11111111 11111111 11111110 00000000	255.255.254.0
CIDR	/24	256	11111111 11111111 11111111 00000000	255.255.255.0
CIDR	/25	128	11111111 11111111 11111111 10000000	255.255.255.128
CIDR	/26	64	11111111 11111111 11111111 11000000	255.255.255.192
CIDR	/27	32	11111111 11111111 11111111 11100000	255.255.255.224
CIDR	/28	16	11111111 11111111 11111111 11110000	255.255.255.240
CIDR	/29	8	11111111 11111111 11111111 11111000	255.255.255.248
CIDR	/30	4	11111111 11111111 11111111 11111100	255.255.255.252

Subnetting an IP network is to separate a big network into smaller multiple networks. Applying a subnet mask to an IP address separates network address from Host Address.

ARP,DHCP and DNS Concepts

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1. Address Resolution Protocol (ARP)

1- Address resolution protocol (arp)." arp resolves IP addresses used by TCP/IP-based software to media access control addresses used by lan hardware.

2- Arp provides the following protocol services to hosts located on the same physical network.

3- Media access control addresses are obtained by using a network broadcast request in the form of the question "what is the media access control address for a device that is configured with the enclosed IP address?"

4- When an arp request is answered, both the sender of the ARP reply and the original arp requester record each other's IP address and media access control address as an entry in a local table called the arp cache for future reference.

(a) HARDWARE ADDRESSING

1- Hardware built for use on LANs must contain a unique address programmed into the device by the manufacturer. For Ethernet and token ring LAN hardware, this address is known as a media access control address.

2- Each media access control address identifies the device within its own physical network with a 6-byte number programmed into read-only memory (rom) on each physical hardware device, such as a network adapter. media access control addresses are typically displayed in hexadecimal (for example, 00-aa-00-3f-89-4a).

3- Authority and registration of media access control addresses are overseen by the institute of electrical and electronics engineers (IEEE). Currently, the IEEE registers and assigns unique numbers for the first three bytes of the media access control address to individual manufacturers. Each manufacturer can then assign the last three bytes of the media access control address to individual network adapters.

　

(b) HOW ARP RESOLVES MEDIA ACCESS CONTROL

(i) Host A is assigned the IP address of 10.0.0.99 and Host　B is assigned the IP address of 10.0.0.100.

(ii) When Host A tries to communicate with Host　B, the following steps resolve Host　B’s software-assigned address (10.0.0.100) to Host　B’s hardware-assigned media access control address.

(iii) Based on the contents of the routing table on Host A, IP determines that the forwarding IP address to be used to reach Host　B is 10.0.0.100. Host A then checks its own local arp cache for a matching hardware address for Host　B.

(iv) If Host A finds no mapping in the cache, it broadcasts an arp request frame to all hosts on the local network with the question "what is the hardware address for 10.0.0.100?" both hardware and software addresses for the source, Host A, are included in the arp request.

(v) Each host on the local network receives the arp request and checks for a match to its own IP address. If a host does not find a match, it discards the ARP request.

(vi) Host　B determines that the IP address in the ARP request matches its own IP address and adds a hardware/software address mapping for Host A to its local ARP cache.

(vii) Host　B sends an ARP reply message containing its hardware address directly back to Host A. When Host A receives the ARP reply message from Host　B, it updates its ARP cache with a hardware/software address mapping for Host　B.

(viii) Once the media access control address for Host　B has been determined, Host A can send IP traffic to Host　B by addressing it to Host　B’s media access control address.

(i) To minimize the number of broadcasts, ARP maintains a cache of IP address–to–media access control address mappings for future use.

(ii) The ARP cache can contain both dynamic and static entries.

(iii) Dynamic entries are added and removed automatically over time

(iv) Static entries remain in the cache until the computer is restarted.

(v) Each dynamic ARP cache entry has a potential lifetime of 10　minutes.

(vi) New entries added to the cache are time stamped. if an entry is not reused within 2　minutes of being added, it expires and is removed from the ARP cache.

(vii) If an entry is used, it receives two more minutes of lifetime. If an entry keeps getting used, it receives an additional two minutes of lifetime up to a maximum lifetime of 10　minutes.

　

　

　

(d) ARP COMMAND

1- To view the arp cache, type arp　–a at a command prompt.

2- To view arp command-line options, type arp　/? at a command prompt

3- There is a separate arp cache for each network adapter.

4- To display the arp cache tables for all interfaces, type: arp –a

5- To display the arp cache table for the interface that is assigned the IP address 10.0.0.99, type: arp -a -n 10.0.0.99

6- To add a static arp cache entry that resolves the IP address 10.0.0.80 to the physical address 00-aa-00-4f-2a-9c, type: arp -s 10.0.0.80 00-aa-00-4f-2a-9c

2. Dynamic Host Configuration Protocol

1- It gives IP addresses automatically to the clients who are requesting for a dynamic IP address

2- DHCP uses a client/server model where the DHCP server maintains centralized management of IP address that are used on the network.

3- DHCP provides safe, reliable and simple TCP/IP network configuration.

4- DHCP prevents address conflicts and helps conserve the use of client IP addresses on the network

How DHCP Works

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(a) Dynamic Host Configuration Protocol (DHCP)

1- The dynamic host configuration protocol (DHCP) enables computers to receive TCP/IP configuration settings automatically.

2- A DHCP server computer can configure a DHCP client with an IP address and a subnet mask.

3- The DHCP client can also receive other settings from DHCP, such as IP addresses for the default gateway, DNS servers, and WINS server.

4- DHCP is a protocol used to automatically assign TCP/IP configuration parameters to computers. A DHCP server can supply a DHCP client with a number of TCP/IP settings, such as an IP address, subnet mask, and DNS server.

5- If the DHCP server is assigning the IP addresses, only the DHCP server must be configured with IP address information. The only parameter you need to configure on the client end is an option for the client to receive IP address information from the server. The rest of the configuration takes place from the server side manually.

(b) DHCP DISCOVER

1- The DHCP client initiates the process by broadcasting a datagram destined for UDP port 68 (used by BOOTP and DHCP servers).

2- This first datagram is known as a DHCP Discover message, which is a request to any DHCP server that receives the datagram for configuration information.

3- The DHCP discover datagram contains many fields, but the one that is most important contains the physical address of the DHCP client.

1- A DHCP server configured to lease addresses for the network on which the client computer resides constructs a response datagram known as a DHCP offer and sends it via broadcast to the computer that issued the DHCP discover.

2- This broadcast is sent to UDP port 67 and contains the physical address of the DHCP client.

3- Also contained in the DHCP offer are the physical and IP addresses of the DHCP server, as well as the values for the IP address and subnet mask that are being offered to the DHCP client.

(d) DHCP REQUEST

1- The client selects an offer and constructs and broadcasts a DHCP request datagram.

2- The DHCP request datagram contains the IP address of the server that issued the offer and the physical address of the DHCP client. The DHCP request performs two basic tasks. First it tells the selected DHCP server that the client requests it to assign the DHCP client an IP address (and other configuration settings). Second, it notifies all other DHCP servers with outstanding offers that their offers were not accepted.

(e) DHCP ACK When the DHCP server from which the offer was selected receives the DHCP request datagram, it constructs the final datagram of the lease process. This datagram is known as a DHCP ack (short for acknowledgement).

The DHCP ack includes an IP address and subnet mask for the DHCP client. Optionally, the DHCP client is often also configured with IP addresses for the default gateway, several DNS servers, and possibly one or two WINS servers. In addition to IP addresses, the DHCP client can receive other configuration information such as a NetBIOS node type, which can change the order of NetBIOS name resolution.

3. DNS(Domain Name System)

1- DNS is a system used for translating domain names into IP addresses in a TCP/IP based network. The process of resolving a domain name to IP address is called name resolution. The domain name space is a tree-like structure representing all the domains that make up the name space for the Internet. The root domain is at the top of the tree.

2- Defines a hierarchical namespace where each level of the namespace is separated by a "."

3- Provides resolution of names to IP addresses and resolution of IP addresses to names.

4- Capabilities vary by operating system and/or DNS server software version.

5- DNS provides a hierarchical structure. Called domain namespace, for managing the DNS database. The hierarchical structure includes:

Root domain Situated at the top of the domain structure and it is represented by a period (.)

Top-level domain Situated below the root domain and used to represent the type of organization. Following are the top –level domains available.

DNS NAME SPACE

　

　

4. QUERY AND LOOKUP TYPES

Query Types
Iterative query	The DNS server returns an answer to the query or a pointer to other DNS servers
Recursive query	The DNS server returns a complete answer to the query, not a pointer to another DNS server
Lookup Types
Forward lookup	Requests name-to-address resolution
Reverse lookup	Requests address-to-name resolution

5. DNS Zone Types: Forward and Reverse Lookup

　

　

　
　

　

6. RECURSIVE QUERIES

*A query made from a client to a DNS server in which the server assumes the full *workload

*DNS server returns either a complete answer or negative

*Issued by -

*Client computers

*DNS servers configured to use forwarder(s)

7. ITERATIVE QUERIES

1- Receiving server may return an answer, a negative response, or a referral to other DNS server(s).

2- Typically issued by DNS servers not configured to use forwarders for resolution of queries.

3- "Walk" the DNS tree.

4- "Give me an answer or refer me to somebody else who can help me obtain resolution."

About Me & My Blog

Hello guys I am Sourav Kumar Patel I am pursuing my BE degree from IIT Kanpur in Computer Engineering. One of the top wellknown and reputed colleges of India.

I am interested in how computing is creating new opportunities for enterprises of all sizes and how “Clouds”, or cloud services, in general are truly changing the landscape of traditional IT and telco services, resource and service provisioning.

With this blog, my objective is to create an interesting blog site that contains relatively short posts (articles), explaining some of the key elements related computing, technologies and services as well as to publish related news summaries and, finally, to add my own opinions when appropriate.

Please feel free to add your comments to my posts and I will try to answer any questions the best I can.

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