What is Cloud Computing?

Cloud computing is the on-demand delivery of compute power, database storage, applications, and other IT resources through a cloud services platform via the internet with pay-as-you-go pricing.

Cloud Computing Basics

Whether you are running applications that share photos to millions of mobile users or you’re supporting the critical operations of your business, a cloud services platform provides rapid access to flexible and low cost IT resources. With cloud computing, you don’t need to make large upfront investments in hardware and spend a lot of time on the heavy lifting of managing that hardware. Instead, you can provision exactly the right type and size of computing resources you need to power your newest bright idea or operate your IT department. You can access as many resources as you need, almost instantly, and only pay for what you use.

How Does Cloud Computing Work?

Cloud computing provides a simple way to access servers, storage, databases and a broad set of application services over the Internet. A Cloud services platform such as Amazon Web Services owns and maintains the network-connected hardware required for these application services, while you provision and use what you need via a web application.

Six Advantages and Benefits of Cloud Computing

 Trade capital expense for variable expense

Instead of having to invest heavily in data centers and servers before you know how you’re going to use them, you can only pay when you consume computing resources, and only pay for how much you consume.

 Benefit from massive economies of scale

By using cloud computing, you can achieve a lower variable cost than you can get on your own. Because usage from hundreds of thousands of customers are aggregated in the cloud, providers such as Amazon Web Services can achieve higher economies of scale which translates into lower pay as you go prices.

 Stop guessing capacity

Eliminate guessing on your infrastructure capacity needs. When you make a capacity decision prior to deploying an application, you often either end up sitting on expensive idle resources or dealing with limited capacity. With cloud computing, these problems go away. You can access as much or as little as you need, and scale up and down as required with only a few minutes notice.

 Increase speed and agility

 In a cloud computing environment, new IT resources are only ever a click away, which means you reduce the time it takes to make those resources available to your developers from weeks to just minutes. This results in a dramatic increase in agility for the organization, since the cost and time it takes to experiment and develop is significantly lower.

 Stop spending money on running and maintaining data centers 

Focus on projects that differentiate your business, not the infrastructure. Cloud computing lets you focus on your own customers, rather than on the heavy lifting of racking, stacking and powering servers.

 Go global in minutes

Easily deploy your application in multiple regions around the world with just a few clicks. This means you can provide a lower latency and better experience for your customers simply and at minimal cost.

Types of Cloud Computing

Cloud computing has three main types that are commonly referred to as Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). Selecting the right type of cloud computing for your needs can help you strike the right balance of control and the avoidance of undifferentiated heavy lifting.

 Cloud Solutions 

Hundreds of thousands of customers have joined the Amazon Web Services (AWS) community and use AWS solutions to build their businesses. The AWS cloud computing platform provides the flexibility to build your application, your way, regardless of your use case or industry. You can save time, money, and let AWS manage your infrastructure, without compromising scalability, security, or dependability.  

Types of Windows Application Pools

 The configuration settings for all application pools running on the Internet Information Service (IIS) 7 are the main elements of an application pool. Application pools contain one or more worker process. Application pool is assigned with the common settings, which are used to serve for one or more requests. The worker process are then configured and assigned to the application pool. The isolation from one web application from another web application is achieved because of the application pool, which allows the web applications to share one or more similar configured worker process. Any error in one application pool does not affect websites or applications in another application pool. This is implemented by the boundaries set for the process of each worker process.

In IIS 7 and later, each application pool uses one of two .NET integration modes for running ASP.NET applications: Integrated or Classic. The .NET integration mode defined for the application pool determines how IIS processes an incoming request to the sites, applications and Web services that run in that application pool.

Integrated

Integrated mode is the default mode by which all the application pools in the IIS 7 and later runs. This mode allows all the ASP.NET modules to be a part in IIS request process without checking the type of resource requested. In this integrated mode all the features of the ASP.Net 2.0 request pipeline are made available to the requests for static content, as well as ASP, PHP, and other content types.

Classic

In Classic mode the asp.net applications are hosted by the IIS 6.0 processing pipe line. In this mode, The ASP.NET requests are processed first through the IIS 7 and later modules. Also ASP.NET requests are then processed by the aspnet_isapi.dll. The IIS 7, later processing pipe lines, and the ASP.NET pipelines are separate from each other. The other resource types do not get the features of the ASP.NET request processing pipelines. This indicates the fact that ASP.NET request should undergo through authentication and authorization modules in both process models. However, Classic mode is not as efficient as integrated mode. Classic mode is not compatible with applications that were developed using ASP.NET version 1.1 on an IIS 7 and later server. It cannot be ran without modifying the application in integrated mode.

The Application Pool Identity type is a feature in new IIS 7.5 and above editions, which is used for identity attribute of the <processModel> element. This process identity feature is a default for applications, and allows to secure the content areas to allow a specific application pool. This security feature can be enabled using the name of an application pool by using syntax “IIS AppPool\DefaultAppPool.” The surface attack area of the server is reduced severely because the identity feature is created dynamically.

How to Fix Temporary Profile in Windows 7

How to Fix Windows 7 Temp Issue on Workgroup and Domain Environment

1) Before do anything, restart the computer 2 or 3 times to see whether it’s going back to your old correct profile. Go to next step if this doesn’t work.

2) Rename the temp profile registry and revert back the old registry settings for the correct profile. This method works most of the time for me in Workgroup and domain environment.

a)  Log in with temp profile.
b) Start registry editor by typing regedit in find box of Windows 7.
c)  Navigate the following location.

d)      You will see similar keys under profile list, but one with .bak, as shown below

e)      The key with .bak is for the correct old profile. Currently your Windows 7 computer logged in with fresh (temporary) profile with same key. So, rename the new profile key ( which is not having.bak) and remove .bak from correct profile key. See below.

f)      That’s it. Log off and log in (or restart) with your user name and password. You must get your correct profile with icons and profile settings back in Windows 7, if you are lucky enough.

Still if Windows 7 computer loads with temporary profile and creates a registry key with .bak, that means user profile is really corrupted and Operating System is not reading it properly.

3) Few times this method worked for me,  repair the corrupted files. Usually the corrupted ‘Ntuser’ files cause this issue. So, run the check disk for partition which is having user profile.

After restarting for check disk, if you see corrupted entries and repairing process inside your user profile folder, then you can hope for good news here. If it finds and repairs any files especially Ntuser files, you may get your old Windows 7 profile back.

If above steps do not help you out, then we need to create a new profile with new user name.

4) Create new user name in non domain (workgroup environment) from control panel or computer management.  Make sure to add the new user to administrators group.ogin with new user name and start copying your old data from old profile. I normally copy below data,

a) My Documents (Music, videos and downloads)
b) Desktop
c) Favorites
d) Any outlook PST files 

5) New user profile in domain environment.

Since we can’t delete and create new domain user account for this purpose, we will play around with client computer only. Let’s completely remove the user profile and re create again.

Copy the important user data (a to d in above step 4) or entire folders from corrupted profile to new location. Double-check that you have copied all required folders and files from old profile, because we are going to delete it now.

Go to Advanced settings of System as shown below, click on Settings (user profiles), select the corrupted user profile which is not loading properly in Windows 7, then press Delete button. Delete button will be enabled only if you login with different user account.

This will remove the entire user profile and related user SID from computer including the registery keys we talked about earlier. You can cross check the proper removal of user account (SID) by checking the C:\Usersfolder. Once it is remove properly, restart the computer and login with same user name (which was not loading earlier). The computer should create a new user profile as this is the first time the user is logging on. You need to copy back your old important data to new profile and set email outlook etc..if required.

I hope these tips help to fix temporary profile issue on Windows 7.

What is the difference between a LAN, a MAN, and a WAN?

A LAN (local area network) is a group of computers and network devices connected together, usually within the same building. By definition, the connections must be high speed and relatively inexpensive (e.g., token ring or Ethernet). Most Indiana University Bloomington departments are on LANs.
A LAN connection is a high-speed connection to a LAN. On the IUB campus, most connections are either Ethernet (10 Mbps) or Fast Ethernet (100 Mbps), and a few locations have Gigabit Ethernet (1000 Mbps) connections.
A MAN (metropolitan area network) is a larger network that usually spans several buildings in the same city or town. The IUB network is an example of a MAN.
A WAN (wide area network), in comparison to a MAN, is not restricted to a geographical location, although it might be confined within the bounds of a state or country. A WAN connects several LANs, and may be limited to an enterprise (a corporation or an organization) or accessible to the public. The technology is high speed and relatively expensive. The Internet is an example of a worldwide public WAN.

Types of networks
There are three basic types of networks

LAN

• Local Area Network
• A network on one site such as a school or building
• The physical arrangement of the devices on a LAN is called the topology

WAN

• Wide Area Network
• A collection of LANs
• Connects a series of networks or servers over much larger distance, such as the internet

MAN

• Metropolitian Area Network 
• Typically no longer used as businesses can create their own LANs via an intranet over a WAN.

VPN

• Virtual Private Network
• A highly encrypted LAN that may operate over a WAN

PAN

• Personal Area Network
• Typically a connection of devices between one person
• Bluetooth is the most common connection type

LAN AND WAN NETWORK

LAN MAN&WAN NETWORK

Desktop Support Interview Questions

1) What is active directory?
Active directory authorizes and authenticates all users and computers in a window domain network, ensuring the security of the computer and software. Through active directory various functions can be managed like creating admin users, connecting to printers or external hard drives.
2) What is DHCP and what it is used for?
DHCP stands for dynamic host configuration protocol. It is used to allocate IP addresses to a large number of the computer system in a network.  It helps in managing the large number of IP’s very easily.
3) What is scope and super scope?
Scope consists of an IP address like gateway IP, subnet mask, DNS server IP. It can be used to communicate with the other PCs in the network. The superscope becomes when you combine two or more scopes together.
4) What is DNS?
DNS mean Domain Naming Service and it is used for resolving IP addresses to name and names to IP address. DNS is like a translator for computers, computers understand the number and not the alphabet. For example, if we type like hotmail.com, the computer don’t understand this so they use DNS which converts (hotmail.com) into (numbers) and then executes the command.
5) What is forward and reverse lookup in DNS?
When we convert IP address into names is called Reverse lookup, while converting names into IP address is called Forward lookup.

Desktop Support

6) What is ‘A’ record and what is ‘MX record’?
‘A’ record is also known as host record, and it has ability to map the IP address by name. It is with this record that DNS can find out the IP address of a name. While, ‘MX record’ also known as mail exchanger record, by the help of ‘MX’ record, location of the mail server is identified.  The record is also found in DNS.
7) What is IPCONFIG command?
IPCONFIG command is used to display the IP information of the computer assigned like DNS IP address and gateway IP address.
8) What would you use to connect two computers without using switches?
Cross cables are used to connect two computers without using switches.
9) What is a domain?
Domain is a set of computers which network recognizes by the internet. It can be used by centrally administer computers. It is created when you install active directory.
10) Tell me if your system is infected by a virus how you will recover the data?
You need to re-install another system, latest anti-virus software and an O.S with latest patches.  Before you start your system, connect the infected HDD as a secondary drive then scan and clean the infected hard drive. Once done, you can copy the files into the system.
11) What is the operating system?
Operating system acts as an interpreter between computer application and hardware.  It works as an user interface.
12) What are the types of operating system or O.S?
The two types of operating systems are:

• NOS : Network Operating System. Examples of NOS- Windows NT, 2000,2003
• SOS : Simple Operating System. Examples of SOS – Windows 95,98, ME

13) Explain about RAS server?
RAS means Remote Access Server.  It allows operating the tool or information that typically resides on a network or IT devices through combination of hardware and software, for example connecting to printer or file. It is usually used for mobile users who are in the network. It uses telephone line to provide connectivity to its users. It can also connect two or more than two offices in the network.
14) Explain about VPN server?
VPN means Virtual Private Network. It is a private communications network often used by companies or organizations to communicate confidentially over a public network.  This is used by the mobile users in the network.
15) What is the difference between RAS and VPN server?
RAS is truly a local area connection between two connections whereas, VPN is a local connection spread over large area.
16)  What is IAS server?
IAS means Internet Authentication Service. For many types of network access like wireless, authenticating switch and remote access dial-up they perform accounting and auditing, centralized connection authentication and authorization.
17) What is Ping command?
Between two or more devices, to check the physical IP connectivity Ping command is used.
18) What do you mean by clustering? What are the benefits?
When one or more computers work together as a single system by sharing their resources is known as clustering.  The benefits of clustering are that it reduces the load on one single system by sharing the load also it is used for redundancy of the services.
19) What is a group?
Group is a collection of the user account. It provides the simplified administration in the network.
20) What is a child domain?
A child domain is the member domain of Windows 2000 Active Directory.
21) What are the benefits of a child domain?
Benefits of child domain are:

• Low network traffic
• Low administrative overhead
• Security boundary

22) What is OU?
OU means for Organizational Unit. It is a container within Active Directory which can hold users, groups and computers.  It is the smallest unit on which administrator can assign group policy settings.
23) Explain group policy?
Group policy provides the stream line access to all the users in the network, it can be used to define the users security and networking policies.  By group policy you can keep control over certain function like not allowing the users to shut down the system or using the control panel or running the command. Group policy is applicable on active directory container like OU, site and Domain.
24) What is the difference between permission, rights and policy?
“Policy” is assigned on active directory, like site, domain and OU. The “Rights” are assign to users and groups, whereas, the “Permission” is assigned for network resources like file, folders and printers.
25) What is DC and ADC stands for?
DC stands for domain controller and ADC stands for additional domain controller.
ADC is a backup of domain controller. Domain controller is a server that checks the security measures like user id, password.
26) What is the difference between DC (Domain controller) and ADC ( Additional Domain Controller)?
There is one difference between domain controller and additional domain controller, on DC all five operational roles are available while in ADC only three operational role is available.27) What are the operational roles for DC (Domain controller) and ADC ( Additional Domain Controller)?
Operational roles for DC (Domain controller) are:

• Domain Naming Master
• Schema Master
• RID Master
• PDC Emulator
• Infrastructure Master

Operational roles for ADC (Additional Domain Controller) are:

• PDC Emulator
• RID Master
• Infrastructure Master

28) What is a “Default Gateway”?
Default gateway is the IP address of the router in the network.  In any case, if the users wants to switch on to another network, or if they cannot locate their particular network than their query will be forwarded to default gateway.
29) How you can take backup of emails in ms outlook?
To take a back-up in the ms outlook, you have to go in control panel. In control panel you have to go under mail option and then open the data file, select personal folder and click on open folder. After that, you have to copy .pst and have to paste it wherever you want the backup.
30) What is trusting domain and trusted domain?
In trusting domain resources are available, while in trusted domain user’s account is available.
31) What is BUS speed?
The rate of communication speed between microprocessor and RAM is known as BUS speed.
32) Name the Active Directory Partitions?
There are three types of active directory partitions

• Schema partition
• Configuration partition
• Domain partition

33) What is Fixboot?
Fixboot write a new partition boot sector on to the system partition.
34) How many logical drive is it possible to fit on to a physical disk?
The maximum number of the logical drive that can fit on a physical disk is 24, while the extended partition can only have 23 logical drives.
35) What is B Router?
B router means Bridge router. To provide communication between two or more different network like computer to computer or computer to internet, B Router is used.
36) What is the major difference you can mention about Gateway and Router?
Gateway works on different network architecture and router works on same network architecture.
37) What is packet?
A packet is a logical grouping of information that comprises a header which contains user data and location information.
38) What is SCSI?
SCSI stands for Small Computer System Interface. It is a standard electronic interface that allows personal computers to communicate with peripheral hardware such as disk drives, tape drives, printers, CD-ROM drives. In “SCSI” the rate of data transmission is fast.
39) How many classes are there for “IP addresses” and what are the ranges?
They are segregated into five classes

1. Class A  ===      0 -126 ( 127 is reserved for loop back)
2. Class B  ====   128- 191
3. Class C  ====   192-223
4. Class D  ====   224-239
5. Class E  ====   240-255

40) Explain the term FIXMBR?
FIXMBR it is a repair tool. It repairs the Master boot record of the Partition Boot Sector.
41) Explain the term SID?
SID stands for Security Identifier. Every computer object has a unique ID which is known as SID.
42) What is the difference between incremental backup and differential backup?
In incremental backup only incremental parts are backup and not the full back up, while in differential backup we take full back up after the normal backup.
43) What is the difference between server OS and desktop OS?
Server OS gives centralized administration for users, shared resources and security while desktop OS gives access to only local administration.
44) What is the difference between the MSI file and .EXE file?
MSI (Microsoft Installer) allows install, uninstall and repair the program with a single file, while .EXE file needs two files to install and uninstall the software. Also,.EXE file is able to detect the existing version of the software and give option to user to uninstall the program while MSI will instruct the users to use the add and remove program in control panel to remove the existing product first and then you can install the new program.
45) What is BSOD? How do you troubleshoot it?
BSOD stands for blue screen of death. When there is some fault in OS or hardware then Windows can’t run the program and gives a blue screen with a code. To resolve this problem the best way is to reboot the system.  If it doesn’t work than boot the system in the safe mode.
46) What is PTR (Program Troube Record) record?
This program record is used to check if the server name is connected with the IP address, it is exactly opposite to the ‘A’ record. This record is basically created in reverse lookup zone, so it is also known as Reverse DNS records or pointer record.
PTR record= Give me an IP address and I will give you the name
‘A’ record= Give me the name and I will give you the IP address
47)  What is reservation?
Basically the term “Reservation” is used in DHCP server. Some network equipment or computer system needs a specific IP address, in such case we make a reservation in DHCP server for that particular computer system.  By creating reservation it gives access to that particular IP address and at the same time prevents other computer system to use that IP address.
48) What is SMTP server or POP server?
SMTP stands for simple mail transfer protocol. It is basically used for sending and receiving the mail, whereas, POP stands for post office protocol it is used for mail receiving purpose in the network.
49) What is RIS and why you use RIS?
RIS stands for remote installation services. It is used to install image from a Window server to a new hardware.  We use RIS because installing OS every time using a CD would be more time consuming.
50) What is “Bootloader”?
Bootloader facilitates the loading of operating system on the system. It enables the booting process and gives OS option to the users while starting the system.

51) Which Windows OS are you most comfortable with?
 This is a very basic question and you can prepare your answer by researching which OS version is used by the company you’re applying in. Be sure to do a little reading on the systems you are familiar with, so you can showcase your skills.
52) Why do we use DHCP?
Dynamic Host Configuration Protocol (DHCP) is us to assign dynamic IP addresses to network devices, allowing them to have a different IP address each time they are connected to the network.
53) What is DNS and why do we use it on workstations?
The Domain Name System (DNS) is used to resolve human-readable hostnames like www.intenseschool.com into machine-readable IP addresses like 69.143.201.22. The DNS address is configured on workstations. Windows redirects all domain names to resolve into IP addresses.
54) What is a default gateway? What happens if I don’t have one?
A default gateway is a routing device used to forward all traffic that is not addressed to a destination within the local network or local subnet. If you don’t have a default gateway, it is not possible to communicate with the network device/host of different networks. Dial-up internet connections do not require a default gateway though because it is present in the ISP itself.
55) How do I find the path that a packet takes to its destination?
Using “tracert” command lets you see the path travelled by a packet to its destination.
56) What is the use of Safe Mode? When should we use it in Windows?
Often, we have to start Windows in Safe Mode in order to remove spyware or for troubleshooting driver problems and other diagnostic purposes. Only specific programs and files with limited driver support are needed to run the operating system. This will allow you to attempt to remove viruses, change bad drivers and perform other diagnostic tasks that cannot be done in Normal Mode.
57) How do I start in Safe Mode?
Method 1: Reboot the computer. Start pressing the F8 key as soon as your system starts to boot. This will open multiple boot options including Safe Mode.
Method 2: Open Run, type “msconfig” and press Enter. A system configuration window will pop up; now go to the Boot tab, check the “Safe boot” box and select “Minimal” for a typical safe boot. Click Apply and your computer will boot into Safe Mode the next time it restarts.
58) What is the use of the BOOT.ini file?
Boot.ini files are required in booting Windows operating systems, starting with Windows NT. The boot.ini file also provides flexibility for dual booting multiple operating systems on the same computer.
59) How do I edit my Boot.ini?
From Windows:
Open Run, type “msconfig” and press Enter to open System Configuration Utility. Select the tab labelled BOOT.INI. Click the button labelled Check All Boot Paths. A dialog box will open detailing the location of any invalid operating system locations.
60) Which command is used to check IP configuration?
You can use ipconfig /all to display all of the current TCP/IP configuration values, including the IP address, subnet mask, default gateway, and Windows Internet Naming Service (WINS) and DNS configurations.
61)How can I make my hard disk dynamic?
Go to Run then type diskmgmt.msc. After that, right click on hard disk to convert a basic disk to dynamic disk.
Note: You should be logged in with an administrator account.
62) What is the blue screen of death?
A Blue Screen error is mainly due to hardware or software incompatibility within the system. The most common reasons for a Blue Screen of Death (BSD) are unwanted software installation, high CPU usage and faulty RAM. Try the following options.
1. Pull out the RAM card, rub it with rubber on the chip side, and re-insert.
2. If a BSD still occurs, try using that RAM on another system.
3. Every BSD has a unique code; try searching it on Google to find a solution.
63) What are some common sources of computer viruses and how can you prevent being infected?

Some common sources are Internet downloads, email attachments, and infected CDs/DVDs. You can use trusted anti-virus software and update it regularly. Make sure it checks every file on the computer. Backup your system periodically in case a major infection occurs, and be aware of all software and programs that run on your computer. Never click a suspicious link or download a suspicious file.
64) Describe some commonly used LAN cables. What is the maximum length of LAN cable for proper communication?

There are mainly two types:

1. Cat 5 (Category 5 where 5 indicates twists per inch) & Cat 5e (5e indicates 5 twists per inch per pair which leads to reduced cross talk). Both Cat 5 & 5e are UTP cables that can support up to 100 Mbps.
2. Cat 6 & 6e are UTP cables that can support up to 1 Gbps.

After about 80 meters (260 feet), you will usually see a reduction in speed.
 65)Windows cannot currently check for updates; what could be the possible reasons?

There could be two possible reasons:

1. Missing/corrupted files
2. Update services down

Method 1: Contact Microsoft: http://support.microsoft.com/mats/windows_update/

Method 2: Please follow the steps below:

a. Go to Run, type “services.msc” without quotes and press Enter.
b. Locate Windows Update.
c. Right click on Service and select Properties.
d. In Start-up type, select Enable.
e. Click Start under Service status.

What is the difference between public and private IP address?

A public IP address is an IP address that can be accessed over the Internet. Like postal address used to deliver a postal mail to your home, a public IP address is the globally unique IP address assigned to a computing device. Your public IP address can be found at What is my IP Address page. Private IP address on the other hand is used to assign computers within your private space without letting them directly expose to the Internet. For example, if you have multiple computers within your home you may want to use private IP addresses to address each computer within your home. In this scenario, your router get the public IP address, and each of the computers, tablets and smartphones connected to your router (via wired or wifi) get a private IP address from your router via DHCP protocol.
Internet Assigned Numbers Authority (IANA) is the organization responsible for registering IP address ranges to organizations and Internet Service Providers (ISPs). To allow organizations to freely assign private IP addresses, the Network Information Center (InterNIC) has reserved certain address blocks for private use. The following IP blocks are reserved for private IP addresses.

Class	Starting IP Address	Ending IP Address	# of Hosts
A	10.0.0.0	10.255.255.255	16,777,216
B	172.16.0.0	172.31.255.255	1,048,576
C	192.168.0.0	192.168.255.255	65,536

What is public IP address?

A public IP address is the address that is assigned to a computing device to allow direct access over the Internet. A web server, email server and any server device directly accessible from the Internet are candidate for a public IP address. A public IP address is globally unique, and can only be assigned to an unique device.

What is private IP address?

A private IP address is the address space allocated by InterNIC to allow organizations to create their own private network. There are three IP blocks (1 class A, 1 class B and 1 class C) reserved for a private use. The computers, tablets and smartphones sitting behind your home, and the personal computers within an organizations are usually assigned private IP addresses. A network printer residing in your home is assigned a private address so that only your family can print to your local printer.
When a computer is assigned a private IP address, the local devices sees this computer via it's private IP address. However, the devices residing outside of your local network cannot directly communicate via the private IP address, but uses your router's public IP address to communicate. To allow direct access to a local device which is assigned a private IP address, a Network Address Translator (NAT) should be used.

f. Click OK.
66)What is the SysWOW64 folder?

It is normally found in a 64-bit OS, for example 64bit Win7. This folder is very similar to the system32 folder of the 32-bit OS.
67) What do you mean by NTLDR Error?

NTLDR is known as the Network Loader. It helps in loading the operating system. If any system is showing “NTLDR is missing” then you need to copy the NTLDR file from operating system CD.

The 7 Layers of the OSI Model

 The Open System Interconnection (OSI) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare the different layers of the OSI model and understand how they interact with each other.

 

 

 

Physical (Layer 1)

This layer conveys the bit stream - electrical impulse, light or radio signal — through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Layer 1 Physical examples include Ethernet, FDDI, B8ZS, V.35, V.24, RJ45.

Data Link (Layer 2)

At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Layer 2 Data Link examples include PPP, FDDI, ATM, IEEE 802.5/ 802.2, IEEE 802.3/802.2, HDLC, Frame Relay.

Network (Layer 3)

This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, inter networking, error handling, congestion control and packet sequencing.

Layer 3 Network examples include AppleTalk DDP, IP, IPX.

Transport (Layer 4)

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Layer 4 Transport examples include SPX, TCP, UDP.

Session (Layer 5)

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Layer 5 Session examples include NFS, NetBios names, RPC, SQL.

Presentation (Layer 6)

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Layer 6 Presentation examples include encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI.

Application (Layer 7)

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Layer 7 Application examples include WWW browsers, NFS, SNMP, Telnet, HTTP, FTP

List of important (TCP/IP)Ports

Port numbers range from 0 to 65536, but only ports numbers 0 to 1024 are reserved for privileged services and designated as well-known ports. This list of well-known port numbers specifies the port used by the server process as its contact port.

Port Number	Description
1	TCP Port Service Multiplexer (TCPMUX)
5	Remote Job Entry (RJE)
7	ECHO
18	Message Send Protocol (MSP)
20	FTP – Data
21	FTP – Control
22	SSH Remote Login Protocol
23	Telnet
25	Simple Mail Transfer Protocol (SMTP)
29	MSG ICP
37	Time
42	Host Name Server (Nameserv)
43	WhoIs
49	Login Host Protocol (Login)
53	Domain Name System (DNS)
69	Trivial File Transfer Protocol (TFTP)
70	Gopher Services
79	Finger
80	HTTP
103	X.400 Standard
108	SNA Gateway Access Server
109	POP2
110	POP3
115	Simple File Transfer Protocol (SFTP)
118	SQL Services
119	Newsgroup (NNTP)
137	NetBIOS Name Service
139	NetBIOS Datagram Service
143	Interim Mail Access Protocol (IMAP)
150	NetBIOS Session Service
156	SQL Server
161	SNMP
179	Border Gateway Protocol (BGP)
190	Gateway Access Control Protocol (GACP)
194	Internet Relay Chat (IRC)
197	Directory Location Service (DLS)
389	Lightweight Directory Access Protocol (LDAP)
396	Novell Netware over IP
443	HTTPS
444	Simple Network Paging Protocol (SNPP)
445	Microsoft-DS
458	Apple QuickTime
546	DHCP Client
547	DHCP Server
563	SNEWS
569	MSN
1080	Socks