CCNA VLan Basic knowledge

CCNA VLan Basic knowledge
Some basic knowledge of LANs, different topologies, and working of Local Area Networks is required to proceed further.

What is a VLAN?

To refresh your memory, a Local Area Network (LAN) is a set of connected devices like computers, hubs, and switches sharing the same pool of logical address space. Normally, a router is required to route packets from one LAN to another LAN. Traditionally, all packets within a LAN are broadcast to all other devices connected to that particular LAN.

As a result, a traditional LAN has several disadvantages as below:

* Usable bandwidth is shared among all the devices connected to the LAN
* ALL devices connected within a LAN can hear ALL the packets irrespective of whether the packet is meant for that device or not. It is possible for some unscrupulous node listening to data packets not meant for that.
* Suppose, your organization has different departments. Using a traditional LAN, when any changes take place within the organization, physical cables and devices need to be moved to reorganize the LAN infrastructure.
* A LAN cannot extend beyond its physical boundary across a WAN as in VLANs.

If you are looking for a simple networked solution for a small office, it may be a good idea to have a traditional LAN setup with a few hubs or switches. However, if you are planning for a large building or campus wide LAN for several individual departments, a VLAN is almost essential.

Virtual LANs (VLANs) can be considered as an intelligent LAN consisting of different physical LAN segments enabling them to communicate with each other as if they were all on the same physical LAN segment.

Benefits of VLAN: Several of the disadvantages of traditional LANs can be eliminated with the implementation of VLANs.

1. Improved Performance: In a traditional LAN, all the hosts within the LAN receive broadcasts, and contend for available bandwidth. As a result, the bandwidth is shared among all the connected devices within the LAN segment. If you are running high-bandwidth consumption applications such as groupware or server forms, a threshold point may easily be reached. After a threshold, the users may find the LAN too slow or un-responsive. With the use of VLAN, you can divide the big LAN into several smaller VLANs. For example, if there are two file servers, each operating at 100Mbps, in a traditional LAN both the servers have to share the LAN bandwidth of 100Mbps. If you put both the servers in separate VLANs, then both have an available bandwidth of 100Mbps each. Here the available bandwidth has been doubled.

2. Functional separation of an institute or a company: It is often required to separate the functional groups within a company or institute. For example, it might be necessary to separate HR department LAN from that of Production LAN. Traditionally, it requires a router to separate two physical LANs. However, you can set up two VLANs, one for Finance, and the other for Production without a router. A switch can route frames from one VLAN to another VLAN. With VLAN's it is easier to place a workgroup together eventhough they are physically in different buildings. In this case Finance VLAN does not forward packets to Production VLAN, providing additional security.

3. Ease of Network Maintenance:

Network maintenance include addition, removal, and changing the network users. With traditional LANs, when ever a User moves, it may be necessary to re-configure the user work station, router, and the servers. Some times, it may also be necessary to lay the cable, or reconfigure hubs and switches. If you are using VLANs, many of these reconfiguration tasks become unnecessary. For example, you can avoid network address configuration on the work station and the corresponding router if you use VLAN. This is because, routing traffic within VLANs doesn't require a router.

However, VLAN's add some administrative complexity, since the administration needs to manage virtual workgroups using VLANs.

4. Reduced Cost

VLANs minimize the network administration by way of reduced maintenance on account of workstation addition/deletion/changes. This in turn reduce the costs associated with LAN maintenance.

5. Security

Using a LAN, all work stations within the LAN get the frames meant for all other work stations within the broadcast domain. Since a VLAN splits the broadcast domain into two or more, it is possible to put work stations sharing sensitive data in one VLAN, and other work station in another VLAN. Of course, if two VLANs are not sufficient, you can split the work stations into as many VLANs as required. VLAN's can also be used to set up firewalls, restrict access, and send any intrusion alerts to the administrator.

Router Boot-up Process

Router Boot-up Process
Router Boot-up Process

There are four major phases to the bootup process:
1. Performing the POST
2. Loading the bootstrap program
3. Locating and loading the Cisco IOS software
4. Locating and loading the startup configuration file or entering setup mode

1. Performing the POST
The Power-On Self Test (POST) is a common process that occurs on almost every computer during bootup. The POST process is used to test the router hardware. When the router is powered on, software on the ROM chip conducts the POST. During this self-test, the router executes diagnostics from ROM on several hardware components including the CPU, RAM, and NVRAM. After the POST has been completed, the router executes the bootstrap program.

2. Loading the Bootstrap Program
After the POST, the bootstrap program is copied from ROM into RAM. Once in RAM, the CPU executes the instructions in the bootstrap program. The main task of the bootstrap program is to locate the Cisco IOS and load it into RAM.
Note: At this point, if you have a console connection to the router, you will begin to see output on the screen.

3. Locating and Loading Cisco IOS
Locating the Cisco IOS software. The IOS is typically stored in flash memory, but can also be stored in other places such as a TFTP (Trivial File Transfer Protocol) server.
If a full IOS image can not be located, a scaled-down version of the IOS is copied from ROM into RAM. This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM.
Note: A TFTP server is usually used as a backup server for IOS but it can also be used as a central point for storing and loading the IOS. IOS management and using the TFTP server is discussed in a later course.

4. Locating and Loading the Configuration File
Locating the Startup Configuration File. After the IOS is loaded, the bootstrap program searches for the startup configuration file, known as startup-config, in NVRAM. This file has the previously saved configuration commands and parameters including:
interface addresses
routing information
passwords
any other configurations saved by the network administrator
If the startup configuration file, startup-config, is located in NVRAM, it is copied into RAM as the running configuration file, running-config.
Executing the Configuration File. If a startup configuration file is found in NVRAM, the IOS loads it into RAM as the running-config and executes the commands in the file, one line at a time. The running-config file contains interface addresses, starts routing processes, configures router passwords and defines other characteristics of the router.

Enter Setup Mode (Optional). If the startup configuration file can not be located, the router prompts the user to enter setup mode. Setup mode is a series of questions prompting the user for basic configuration information. Setup mode is not intended to be used to enter complex router configurations, and it is not commonly used by network administrators.
When booting a router that does not contain a startup configuration file, you will see the following question after the IOS has been loaded:

Command Line Interface
Depending on the platform and IOS, the router may ask the following question before displaying the prompt:
Would you like to terminate autoinstall? [yes]:
Press the Enter key to accept the default answer.
Router>
Note: If a startup configuration file was found, the running-config may contain a hostname and the prompt will display the hostname of the router.
Once the prompt displays, the router is now running the IOS with the current running configuration file. The network administrator can now begin using IOS commands on this router.
Note: The bootup process is discussed in more detail in a later course.

Windows ARP Spoofer 0.5.3

Windows ARP Spoofer 0.5.3
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Windows ARP Spoofer 0.5.3 (Size: 7,5 MB)

Windows ARP Spoofer (WinArpSpoof) is a program that can scan the computers including network devices and can spoof their ARP tables on local area network and can act as a router while pulling all packets on LAN.

Download Link
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The Elements of a NetworksV

The Elements of a NetworksV

We close this section with an example to tie together how the elements of networks - devices, media, and services - are connected by rules to deliver a message. People often only picture networks in the abstract sense. We create and send a text message and it almost immediately shows up on the destination device. Although we know that between our sending device and the receiving device there is a network over which our message travels, we rarely think about all the parts and pieces that make up that infrastructure.

The Messages

In the first step of its journey from the computer to its destination, our instant message gets converted into a format that can be transmitted on the network. All types of messages must be converted to bits, binary coded digital signals, before being sent to their destinations. This is true no matter what the original message format was: text, video, voice, or computer data. Once our instant message is converted to bits, it is ready to be sent onto the network for delivery.

The Devices

To begin to understand the robustness and complexity of the interconnected networks that make up the Internet, it is necessary to start with the basics. Take the example of sending the text message using an instant messaging program on a computer. When we think of using network services, we usually think of using a computer to access them. But, a computer is only one type of device that can send and receive messages over a network. Many other types of devices can also be connected to the network to participate in network services. Among these devices are telephones, cameras, music systems, printers and game consoles.

In addition to the computer, there are numerous other components that make it possible for our instant message to be directed across the miles of wires, underground cables, airwaves and satellite stations that might exist between the source and destination devices. One of the critical components in any size network is the router. A router joins two or more networks, like a home network and the Internet, and passes information from one network to another. Routers in a network work to ensure that the message gets to its destination in the most efficient and quickest manner.

The Medium

To send our instant message to its destination, the computer must be connected to a wired or wireless local network. Local networks can be installed in homes or businesses, where they enable computers and other devices to share information with each other and to use a common connection to the Internet.

Wireless networks allow the use of networked devices anywhere in an office or home, even outdoors. Outside the office or home, wireless networking is available in public hotspots, such as coffee shops, businesses, hotel rooms, and airports.

Many installed networks use wires to provide connectivity. Ethernet is the most common wired networking technology found today. The wires, called cables, connect the computers and other devices that make up the networks. Wired networks are best for moving large amounts of data at high speeds, such as are required to support professional-quality multimedia.

The Services

Network services are computer programs that support the human network. Distributed on devices throughout the network, these services facilitate online communication tools such as e-mail, bulletin/discussion boards, chat rooms, and instant messaging. In the case of instant messaging, for example, an instant messaging service, provided by devices in the cloud, must be accessible to both the sender and recipient.

The Rules

Important aspects of networks that are neither devices nor media are rules, or protocols. These rules are the standards and protocols that specify how the messages are sent, how they are directed through the network, and how they are interpreted at the destination devices. For example, in the case of Jabber instant messaging, the XMPP, TCP, and IP protocols are all important sets of rules that enable our communication to occur.

The Elements of a Networks4

The Elements of a Networks4

Human beings often seek to send and receive a variety of message using computer applications; these applications require services be provided by the network. Some of these services include the World Wide Web, e-mail, instant messaging, and IP Telephony. Devices interconnected by medium to provide services must be governed by rules, or protocols. In the chart, some common services and a protocol most directly associated with that service are listed.

Protocols are the rules that the networked devices use to communicate with each other. The industry standard in networking today is a set of protocols called TCP/IP (Transmission Control Protocol/Internet Protocol). TCP/IP is used in home and business networks, as well as being the primary protocol of the Internet. It is TCP/IP protocols that specify the formatting, addressing and routing mechanisms that ensure our messages are delivered to the correct recipient.

The Elements of a Networks3

The Elements of a Networks3
For a network to function, the devices must be interconnected. Network connections can be wired or wireless. In wired connections, the medium is either copper, which carries electrical signals, or optical fiber, which carries light signals. In wireless connections, the medium is the Earth's atmosphere, or space, and the signals are microwaves. Copper medium includes cables, such as twisted pair telephone wire, coaxial cable, or most commonly, what is known as Category 5 Unshielded Twisted Pair (UTP) cable. Optical fibers, thin strands of glass or plastic that carry light signals, are another form of networking media. Wireless media may include the home wireless connection between a wireless router and a computer with a wireless network card, the terrestrial wireless connection between two ground stations, or the communication between devices on earth and satellites. In a typical journey across the Internet, a message may travel across a variety of media.

The Elements of a Networks2

The Elements of a Networks 2
In this course, many networking devices will be discussed. Networking is a very graphically oriented subject, and icons are commonly used to represent networking devices. On the left side of the diagram are shown some common devices which often originate messages that comprise our communication. These include various types of computers (a PC and laptop icon are shown), servers, and IP phones. On local area networks these devices are typically connected by LAN media (wired or wireless).

The right side of the figure shows some of the most common intermediate devices, used to direct and manage messages across the network, as well as other common networking symbols. Generic symbols are shown for:
Switch - the most common device for interconnecting local area networks
Firewall -provides security to networks
Router - helps direct messages as they travel across a network
Wireless Router - a specific type of router often found in home networks
Cloud - used to summarize a group of networking devices, the details of which may be unimportant to the discussion at hand
Serial Link - one form of WAN interconnection, represented by the lightning bolt-shaped line

The Elements of a Networks1

The Elements of a Networks 1
The diagram shows elements of a typical network, including devices, media, and services, tied together by rules, that work together to send messages. We use the word messages as a term that encompasses web pages, e-mail, instant messages, telephone calls, and other forms of communication enabled by the Internet. In this course, we will learn about a variety of messages, devices, media, and services that allow the communication of those messages. We will also learn about the rules, or protocols, that tie these network elements together.

Communication Over Networks

Communication Over Networks
Being able to reliably communicate to anyone, anywhere, is becoming increasingly important to our personal and business lives. In order to support the immediate delivery of the millions of messages being exchanged between people all over the world, we rely on a web of interconnected networks. These data or information networks vary in size and capabilities, but all networks have four basic elements in common:
Rules or agreements to govern how the messages are sent, directed, received and interpreted.
The messages or units of information that travel from one device to another
A means of interconnecting these devices - a medium that can transport the messages from one device to another
Devices on the network that exchange messages with each other

The standardization of the various elements of the network enables equipment and devices created by different companies to work together. Experts in various technologies can contribute their best ideas on how to develop an efficient network, without regard to the brand or manufacturer of the equipment.

1.2.2 Quality of Communication 2

Internal Factors

Internal factors that interfere with network communication are related to the nature of the message itself.

Different types of messages may vary in complexity and importance. Clear and concise messages are usually easier to understand than complex messages. Important communications require more care to ensure that they are delivered and understood by the recipient.

Internal factors affecting the successful communication across the network include:
The size of the message
The complexity of the message
The importance of the message

Large messages may be interrupted or delayed at different points within the network. A message with a low importance or priority could be dropped if the network becomes overloaded.

Both the internal and external factors that affect the receipt of a message must be anticipated and controlled for network communications to be successful. New innovations in network hardware and software are being implemented to ensure the quality and reliability of network communications.

1.2.2 Quality of Communication

Communication between individuals is determined to be successful when the meaning of the message understood by the recipient matches the meaning intended by the sender.

For data networks, we use the same basic criteria to judge success. However, as a message moves through the network, many factors can prevent the message from reaching the recipient or distort its intended meaning. These factors can be either external or internal.

External Factors

The external factors affecting communication are related to the complexity of the network and the number of devices a message must pass through on its route to its final destination.

External factors affecting the success of communication include:
The quality of the pathway between the sender and the recipient
The number of times the message has to change form
The number of times the message has to be redirected or readressed
The number of other messages being transmitted simultaneously on the communication network
The amount of time allotted for successful communication

What is Communication?

The widespread adoption of the Internet by the entertainment and travel industries enhances the ability to enjoy and share many forms of recreation, regardless of location. It is possible to explore places interactively that previously we could only dream of visiting, as well as preview the actual destinations before making a trip. The details and photographs from these adventures may be posted online for others to view.

The Internet is used for traditional forms of entertainment, as well. We listen to recording artists, preview or view motion pictures, read entire books and download material for future offline access. Live sporting events and concerts can be experienced as they are happening, or recorded and viewed on demand.

Networks enable the creation of new forms of entertainment, such as online games. Players participate in any kind of online competition that that game designers can imagine. We compete with friends and foes around the world in the same manner if they were in the same room.

Even offline activities are enhanced using network collaboration services. Global communities of interest have grown rapidly. We share common experiences and hobbies well beyond our local neighborhood, city, or region. Sports fans share opinions and facts about their favorite teams. Collectors display prized collections and get expert feedback about them.

Online markets and auction sites provide the opportunity to buy, sell and trade all types of merchandise.

Whatever form of recreation we enjoy in the human network, networks are improving our experience.

Networks Supporting the Way We Play

The widespread adoption of the Internet by the entertainment and travel industries enhances the ability to enjoy and share many forms of recreation, regardless of location. It is possible to explore places interactively that previously we could only dream of visiting, as well as preview the actual destinations before making a trip. The details and photographs from these adventures may be posted online for others to view.

The Internet is used for traditional forms of entertainment, as well. We listen to recording artists, preview or view motion pictures, read entire books and download material for future offline access. Live sporting events and concerts can be experienced as they are happening, or recorded and viewed on demand.

Networks enable the creation of new forms of entertainment, such as online games. Players participate in any kind of online competition that that game designers can imagine. We compete with friends and foes around the world in the same manner if they were in the same room.

Even offline activities are enhanced using network collaboration services. Global communities of interest have grown rapidly. We share common experiences and hobbies well beyond our local neighborhood, city, or region. Sports fans share opinions and facts about their favorite teams. Collectors display prized collections and get expert feedback about them.

Online markets and auction sites provide the opportunity to buy, sell and trade all types of merchandise.

Whatever form of recreation we enjoy in the human network, networks are improving our experience.

Networks Supporting the Way We Work

Initially, data networks were used by businesses to internally record and manage financial information, customer information, and employee payroll systems. These business networks evolved to enable the transmission of many different types of information services, including e-mail, video, messaging, and telephony.

Intranets, private networks in use by just one company, enable businesses to communicate and perform transactions among global employee and branch locations. Companies develop extranets, or extended internetworks, to provide suppliers, vendors, and customers limited access to corporate data to check order status, inventory, and parts lists.

Today, networks provide a greater integration between related functions and organizations than was possible in the past.

Consider these business scenarios.
A wheat farmer in Australia uses a laptop enabled with a Global Positioning System (GPS) to plant a crop with precision and efficiency. At harvest time, the farmer can co-ordinate harvesting with the availability of grain transporters and storage facilities. Using mobile wireless technology, the grain transporter can monitor the vehicle in-route in order to maintain the best fuel efficiency and safe operation. Changes in status can be relayed to the driver of the vehicle instantly.
Remote workers, called teleworkers or telecommuters, use secure remote access services from home or while traveling. The data network enables them to work as if they were on-site, with access to all the network-based tools normally available for their jobs. Virtual meetings and conferences can be convened which include people in remote locations. The network provides audio and video capability so all participants can both see and hear each other. The information from the meetings can be recorded to a wiki or blog. The latest versions of the agenda and minutes can be shared as soon as they are created.

There are many success stories illustrating innovative ways networks are being used to make us more successful in the workplace. Some of these scenarios are available through the Cisco web site at http://www.cisco.com