Interview Tips

http://www.indiabix.com/technical/networking/

Its not a crack to pass the interview its just a study material to recognize your level of knowledge in networking.

Go through it and update your knowledge.

Your mind should always hungry to get updates.

OSI MODEL

OSI REFERENCE MODEL

OSI (Open Systems Interconnection) is reference model for how applications can communicate over a network. A reference model is a conceptual framework for understanding relationships. The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create will interoperate, and to facilitate clear comparisons among communications tools. Most vendors involved in telecommunications make an attempt to describe their products and services in relation to the OSI model. And although useful for guiding discussion and evaluation, OSI is rarely actually implemented, as few network products or standard tools keep all related functions together in well-defined layers as related to the model. The TCP/IP protocols, which define the Internet, do not map cleanly to the OSI model.

Easy Way To Remember Layers

Please Do Not Take Sales Person Advice

IP Address || Logical Address

• Private IP
• Public IP
• APIPA

NAT(network address translation)

Port Address

0-65535

well known---->     0  -1023

Registered  ----> 1024-49151

Dynamic    ---->  49152-65535

Static and Dynamic

• Static address
• Dynamic address

In IP address network portion is considered as 1's and host portion is considered as 0's.

5 classes

Class A----->  0  -126

Class B----->128-191

Class C----->192-223

Class D----->224-239

Class E----->240-255(Research Purposes)

Dynamic address

DHCP

*Provide dynamic ip address in lease.

APIPA(automatic private ip address)

169.254

DHCP works (DORA)

Address

IP ADDRESSMAC ADDRESSPORT ADDRESS

• IP ADDRESS

An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there.

The designers of the Internet Protocol defined an IP address as a 32-bit number and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, because of the growth of the Internet and the predicted depletion of available addresses, a new version of IP (IPv6), using 128 bits for the address, was developed in 1995.IPv6 was standardized as in 1998,And its deployment has been ongoing since the mid-2000s.

• MAC ADDRESS

A media access control address (MAC address), also called physical address, is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet and WiFi. Logically, MAC addresses are used in the media access control protocol sublayer of the OSI reference model.

MAC addresses are most often assigned by the manufacturer of a network interface controller (NIC) and are stored in its hardware, such as the card's read-only memory or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address (BIA). It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. This can be contrasted to a programmed address, where the host device issues commands to the NIC to use an arbitrary address.

• PORT ADDRESS

In computer networking, a port is an endpoint of communication in an operating system. While the term is also used for hardware devices, in software it is a logical construct that identifies a specific process or a type of service.

A port is always associated with an IP address of a host and the protocol type of the communication, and thus completes the destination or origination address of a communications session. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number.

Specific port numbers are often used to identify specific services. Of the thousands of enumerated ports, 1024 well-known port numbers are reserved by convention to identify specific service types on a host. The protocols that primarily use ports are the transport layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet protocol suite.

In the client–server model of application architecture, the ports that network clients connect to for service initiation provide a multiplexing service. After initial communication binds to the well-known port number, this port is freed by switching each instance of service requests to a dedicated, connection-specific port number, so that additional clients can be serviced.

• https://en.wikipedia.org/wiki/IP_address
• https://en.wikipedia.org/wiki/MAC_address
• https://en.wikipedia.org/wiki/Port_(computer_networking)

From the view of a network engineer this is nothing...

There is lot of things to learn in address.

Please refer to Wiki.

Modem

A modem (modulator-demodulator) is a device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

History

News wire services in the 1920s, used multiplex devices that satisfied the definition of a modem. However the modem function was incidental to the multiplexing function, so they are not commonly included in the history of modems. Modems grew out of the need to connect teleprinters over ordinary phone lines instead of the more expensive leased lines which had previously been used for current loop–based teleprinters and automated telegraphs.

Mass-produced modems in the United States began as part of the SAGE air-defense system in 1958 (the year the word modem was first used^[1]), connecting terminals at various airbases, radar sites, and command-and-control centers to the SAGE director centers scattered around the U.S. and Canada. SAGE modems were described by AT&T's Bell Labs as conforming to their newly published Bell 101 dataset standard. While they ran on dedicated telephone lines, the devices at each end were no different from commercial acoustically coupled Bell 101, 110 baud modems.

The 201A and 201B Data-Phones were synchronous modems using two-bit-per-baud phase-shift keying (PSK). The 201A operated half-duplex at 2,000 bit/s over normal phone lines, while the 201B provided full duplex 2,400 bit/s service on four-wire leased lines, the send and receive channels each running on their own set of two wires.

The famous Bell 103A dataset standard was also introduced by AT&T in 1962. It provided full-duplex service at 300 bit/s over normal phone lines. Frequency-shift keying was used, with the call originator transmitting at 1,070 or 1,270 Hz and the answering modem transmitting at 2,025 or 2,225 Hz. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the Teletype Model 33 ASR and KSR, and the IBM 2741. AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems.

Connection	Modulation	Bitrate [kbit/s]	Year released
110 baud Bell 101 modem	FSK	0.1	1958
300 baud (Bell 103 or V.21)	FSK	0.3	1962
1200 modem (1200 baud) (Bell 202)	FSK	1.2
1200 modem (600 baud) (Bell 212A or V.22)	QPSK	1.2	1980[9][10]
2400 modem (600 baud) (V.22bis)	QAM	2.4	1984[9]
2400 modem (1200 baud) (V.26bis)	PSK	2.4
4800 modem (1600 baud) (V.27ter)	PSK	4.8	[11]
9600 modem (2400 baud) (V.32)	QAM	9.6	1984[9]
14.4k modem (2400 baud) (V.32bis)	trellis	14.4	1991[9]
28.8k modem (3200 baud) (V.34)	trellis	28.8	1994[9]
33.6k modem (3429 baud) (V.34)	trellis	33.6	1996[12]
56k modem (8000/3429 baud) (V.90)	digital	56.0/33.6	1998[9]
56k modem (8000/8000 baud) (V.92)	digital	56.0/48.0	2000[9]
Bonding modem (two 56k modems) (V.92)[13]		112.0/96.0
Hardware compression (variable) (V.90/V.42bis)		56.0–220.0
Hardware compression (variable) (V.92/V.44)		56.0–320.0
Server-side web compression (variable) (Netscape ISP)		100.0–1,000.0

Protocols and Port Numbers

# Copyright (c) 1993-2006 Microsoft Corp.
#
# This file contains the Internet protocols as defined by various
# RFCs.  See http://www.iana.org/assignments/protocol-numbers 
#
# Format:
#
# <protocol name>  <assigned number>  [aliases...]   [#<comment>]

ip            0     IP           # Internet protocol
icmp       1     ICMP         # Internet control message protocol
ggp         3     GGP          # Gateway-gateway protocol
tcp          6     TCP          # Transmission control protocol
egp         8     EGP          # Exterior gateway protocol
pup        12    PUP          # PARC universal packet protocol
udp        17    UDP          # User datagram protocol
hmp       20    HMP          # Host monitoring protocol
xns-idp  22    XNS-IDP      # Xerox NS IDP
rdp        27    RDP          # "reliable datagram" protocol
ipv6       41    IPv6         # Internet protocol IPv6
ipv6-route 43    IPv6-Route   # Routing header for IPv6
ipv6-frag   44    IPv6-Frag    # Fragment header for IPv6
esp            50    ESP          # Encapsulating security payload
ah              51    AH           # Authentication header
ipv6-icmp 58    IPv6-ICMP    # ICMP for IPv6
ipv6-nonxt 59    IPv6-NoNxt   # No next header for IPv6
ipv6-opts   60    IPv6-Opts    # Destination options for IPv6
rvd             66    RVD          # MIT remote virtual disk

Networking cables are used to connect one network device to other network devices or to connect two or more computers to share printer, scanner etc. Different types of network cables like Coaxial cable, Optical fiber cable, Twisted Pair cables are used depending on the network's topology, protocol and size. The devices can be separated by a few meters (e.g. via Ethernet) or nearly unlimited distances (e.g. via the interconnections of the Internet).

While wireless networks are much easier deployed when total throughput is not an issue, most permanent larger computer networks use cables to transfer signals from one point to another.

Twisted pair

Twisted pair cabling is a form of wiring in which pairs of wires (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling outelectromagnetic interference (EMI) from other wire pairs and from external sources. This type of cable is used for home and corporate Ethernet networks.

There are two major types of twisted pair cables: shielded, unshielded.

Ethernet crossover cable

An Ethernet crossover cable is a type of twisted pair Ethernet cable used to connect computing devices together directly that would normally be connected via a network switch,hub or router, such as directly connecting two personal computers via their network adapters. Most current Ethernet devices support Auto MDI-X, so it doesn't matter whether you use crossover or straight cables.

Fiber optic cable

An optical fiber cable consists of a center glass core surrounded by several layers of protective material. The outer insulating jacket is made of Teflon or PVC to prevent interference. Optical fiber deployment is more expensive than copper but offers higher bandwidth and can cover longer distances.

There are two major types of optical fiber cables: short-range multi-mode fiber and long-range single-mode fiber.

Coaxial cable

Coaxial lines confine the electromagnetic wave inside the cable, between the center conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.

The most common use for coaxial cables is for television and other signals with a bandwidth of several hundred megahertz to gigahertz. Although in most homes coaxial cables have been installed for transmission of TV signals, new technologies (such as the ITU-T G.hn standard) open the possibility of using home coaxial cable for high-speed home networking applications (Ethernet over coax).

In the 20th century they carried long distance telephone connections.

Patch cable

A patch cable is an electrical or optical cable used to connect one electronic or optical device to another for signal routing. Devices of different types (e.g. a switch connected to a computer, or a switch connected to a router) are connected with patch cords. Patch cords are usually produced in many different colors so as to be easily distinguishable,and are relatively short, perhaps no longer than two meters. In contrast to on-premises wiring, patch cables are more flexible but may also be less durable.

Power lines

Although power wires are not designed for networking applications, new technologies like Power line communication allows these wires to also be used to interconnect home computers, peripherals or other networked consumer products. On December 2008, the ITU-T adopted Recommendation G.hn/G.9960 as the first worldwide standard for high-speed powerline communications.

Ethernet was developed at Xerox PARC between 1973 and 1974.It was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation.The idea was first documented in a memo that Metcalfe wrote on May 22, 1973, where he named it after the disproven luminiferous ether as an "omnipresent, completely-passive medium for the propagation of electromagnetic waves". In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, and Butler Lampson as inventors.In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper.

Metcalfe left Xerox in June 1979 to form 3Com. He convinced Digital Equipment Corporation (DEC), Intel, and Xerox to work together to promote Ethernet as a standard. The so-called "DIX" standard, for "Digital/Intel/Xerox", specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype-type field. It was published on September 30, 1980 as "The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications" Version 2 was published in November, 1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the same time and resulted in the publication of IEEE 802.3 on June 23, 1983.

Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus. Because Ethernet was able to adapt to market realities and shift to inexpensive and ubiquitous twisted pair wiring, these proprietary protocols soon found themselves competing in a market inundated by Ethernet products, and, by the end of the 1980s, Ethernet was clearly the dominant network technology. In the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, and that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers. This was followed quickly by DEC's Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986, making it one of the largest computer networks in the world at that time. An Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000.By the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was greatly sped up with the introduction of 10BASE-T and its relatively small modular connector, at which point Ethernet ports appeared even on low-end motherboards.

Since then, Ethernet technology has evolved to meet new bandwidth and market requirements.In addition to computers, Ethernet is now used to interconnect appliances and other personal devices.It is used in industrial applications and is quickly replacing legacy data transmission systems in the world's telecommunications networks. By 2010, the market for Ethernet equipment amounted to over $16 billion per year.

Cabling

So how does a physical cable eliminate interference and allow for faster speeds? It does it through wire twisting and isolation. Cable twisting was invented by Alexander Graham Bell in 1881 for use on telephone wires that were run along side power lines. He discovered that by twisting the cable every 3-4 utility poles, it reduced the interference and increased the range. Twisted pair became the basis for all Ethernet cables to eliminate interference between internal wires (XT), and external wires (AXT).

There are two main physical differences between Cat-5 and Cat-6 cables, the number of twists per cm in the wire, and sheath thickness.

Cable twisting length is not standardized, but typically there are 1.5-2 twists per cm in Cat-5(e) and 2+ twists per cm in Cat-6. Within a single cable, each colored pair will also have different twist lengths based on prime numbers so that no two twists ever align. The amount of twists per pair is usually unique for each cable manufacturer. As you can see in the above picture, no two pairs have the same amount of twists per inch.

Shoes

Many Cat-6 cables also include a nylon spline which helps eliminate crosstalk. Although the spline is not required in Cat-5 cable, some manufactures include it anyway. In Cat-6 cable, the spline is not required either as long as the cable tests according to the standard. In the picture above, the Cat-5e cable is the only one with a spline.

While the nylon spline helps reduce crosstalk in the wire, the thicker sheath protects against near end crosstalk (NEXT) and alien crosstalk (AXT) which both occur more often as the frequency (Mhz) increases. In this picture the Cat-5e cable has the thinnest sheath, but it also was the only one with the nylon spline.

Shielded (STP) vs. Unshielded (UTP)

Because all Ethernet cables are twisted, manufactures use shielding to further protect the cable from interference. Unshielded twisted pair can easily be used for cables between your computer and the wall, but you will want to use shielded cable for areas with high interference and running cables outdoors or inside walls.

There are different ways to shield an Ethernet cable, but typically it involves putting a shield around each pair of wire in the cable. This protects the pairs from crosstalk internally. Manufactures can further protect cables from alien crosstalk but screening UTP or STP cables. Technically the picture above shows a Screened STP cable (S/STP).

Solid vs. Stranded

Solid and stranded Ethernet cables refer to the actual copper conductor in the pairs. Solid cable uses a single piece of copper for the electrical conductor while stranded uses a series of copper cables twisted together. There are many different applications for each type of conductor, but there are two main applications for each type you should know about.

Stranded cable is more flexible and should be used at your desk or anywhere you may be moving the cable around often.

Solid cable is not as flexible but it is also more durable which makes it ideal for permanent installations as well as outdoor and in walls.

Now that you know which type of cable you should use, have a look at our guide to making your own Ethernet cable.

Cabling 1

An Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly. It is most often used to connect two devices of the same type: e.g. two computers (via network interface controller) or two switches to each other. By contrast,patch cables or straight through cables are used to connect devices of different types, such as a computer to a router (or network switchor hub).

Many devices today support Auto MDI-X capability, wherein a patch cable can be used in place of a crossover cable, or vice versa, and the receive and transmit signals are reconfigured automatically to yield the expected result.

The RJ45 connector is standardized as the IEC 60603-7 8P8C modular connector with eight conductors. The RJ45S, a similar standard jack once specified for modem or data interfaces, uses a mechanically-keyed variation of the 8P8C body with an extra tab that prevents it from mating with other connectors; the visual difference from the more-common 8P8C is subtle. The original RJ45S keyed 8P2C modular connector had pins 5 and 4 wired for tip and ring of a single telephone line, and pins 7 and 8 shorting a programming resistor,^[7][8] but is obsolete today.

An installer may wire the jack to an arbitrary pinout, or use it as part of a standardized generic structured cabling system such as ISO/IEC 15018 or ISO/IEC 11801, using 8P8C patch panels for both phone and data wiring.