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A reports on Networks technology
Virtual Local Area Network
November 2012
Submitted By: - Shivaji R. Bhodkhe (MCA-1styr)
E-mail:[email protected]
(P.G. Dept. of Computer Science, SGBAU, Amravati-444602)
mailto:[email protected]:[email protected]:[email protected]:[email protected] -
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INDEXContain Page Numbers
1. Abstract
2.Introduction3.Computer Network
1
4. Local-Area Network (LAN)
4.1. Types of Local-Area Networks (LANs)
5.Metropolitan Area Ne twork (MAN)
2
5.1.Types of MAN (metropolitan Area Network)
Technologies
5.2How MAN works
5.3. Advantages of MAN (Metropolitan Area Network)
3
6. Wide area network (WAN) 4
7. Network Devices7.1 Router
5
7.1.1 Why do I need a Router?
7.1.2. Restrict Broadcasts to the LAN
7.1.3. Act as the Default Gateway
7.1.4. Move (route) Data between Networks
6
7.1.5. Learn and Advertise Loop-Free Paths
7.2. Hubs7.3. Switches
7
7.3.1. Types of Network Switch:
7.3.2. Managed Switches:
8
7.3.3. Unmanaged Network Switch:
7.3.4. Smart Switches:
7.3.5. Advantages of Network Switch:
8. Types of VLAN's
8.1. Layer 1 VLAN: Membership by Port
9
8.2. Layer 2 VLAN: Membership by MAC Address
8.3. Layer 2 VLAN: Membership by Protocol Type
8.4. Layer 3 VLAN: Membership by IP Subnet Address
10
8.5 Higher Layer VLAN's
8.6. Types of Connections
8.6.1 Trunk Link
8.6.2 Access Link
11
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8.6.3. Hybrid Link
9. Frame Processing
9.1 Filtering Database
9.2 Static Entries
9.3. Dynamic Entries
12
9.4. Tagging 1310. Summary
11. References
14
12. Abbreviations 15
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Virtual Local Area Network
1. Abstract
The Virtual Local Area Network (VLAN) technology is one of the hottest areas of
networking systems. A VLAN is a logical connection rather than physical that allows
network devices to be combined as "virtual LANs". The VLAN technology functions by
logically segmenting the network into different broadcast domains so that packets can
only delivered between ports with the same VLAN identity (group member). By using
this characteristic of VLAN there is a very flexible mechanism to group the physical ports
together. Wireless networks also need the flexibility to collect more than two devices
equipped with wireless communication and networking capability. In recent years,
wireless network has been attracting a lot of attention due to wireless devices have
enjoyed a tremendous rise in popularity. In order to communicate among some groups of
wireless devices without the convention concept of clusters we propose a novel model to
form the multiple-domain or the multiple-group as "virtual LANs" according to the
logical connection in ad hoc networks. In this paper discuss on single switch VLAN,
multiple switch VLAN and its working methods.
2. Introduction.
A Local Area Network (LAN) was originally defined as a network of computers
located within the same area. Today, Local Area Networks are defined as a single
broadcast domain. This means that if a user broadcasts information on his/her LAN, the
broadcast will be received by every other user on the LAN. Broadcasts are prevented
from leaving a LAN by using a router. The disadvantage of this method is routers usually
take more time to process incoming data compared to a bridge or a switch. More
importantly, the formation of broadcast domains depends on the physical connection of
the devices in the network. Virtual Local Area Networks (VLAN's) were developed as an
alternative solution to using routers to contain broadcast traffic.
3. Computer Network.
A computer network, or simply a network, is a collection ofcomputers and other
hardware interconnected by communication channels that allow sharing of resources and
information. Where at least one process in one device is able to send/receive data to/from
at least one process residing in a remote device, then the two devices are said to be in a
network. Simply, more than one computer interconnected through a communication
medium for information interchange is called a computer network.
http://en.wikipedia.org/wiki/Computershttp://en.wikipedia.org/wiki/Networking_hardwarehttp://en.wikipedia.org/wiki/Networking_hardwarehttp://en.wikipedia.org/wiki/Computers -
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Networks may be classified according to a wide variety of characteristics, such as the
medium used to transport the data,communications protocol used, scale,topology,
benefit, and organizational scope.
Communications protocols define the rules and data formats for exchanginginformation in a computer network, and provide the basis fornetwork programming.
Well-known communications protocols include twoEthernet,a hardware andlink layer
standard that is ubiquitous inlocal area networks,and theInternet protocol suite,which
defines a set of protocols for internetworking, i.e. for data communication between
multiple networks, as well as host-to-host data transfer, and application-specific data
transmission formats.
4. Local-Area Network (LAN)
A local-area network (LAN) is acomputernetwork that spans a relatively small area.Most LANs are confined to a single building or group of buildings; however, one LAN
can be connected to other LANs over any distance via telephone lines and radio waves. A
system of LANs connected in this way is called awide-area network (WAN).
Most LANs connectworkstations andpersonal computers.Eachnode (individual
computer ) in a LAN has its ownCPU with which itexecutesprograms,but it also is able
toaccessdata anddevices anywhere on the LAN. This means that manyusers can share
expensive devices, such aslaser printers,as well as data. Users can also use the LAN to
communicate with each other, by sendinge-mail or engaging inchat sessions.
LANs are capable of transmitting data at very fast rates, much faster than data can be
transmitted over a telephone line; but the distances are limited, and there is also a limit on
the number of computers that can be attached to a single LAN.
4.1. Types of Local-Area Networks (LANs)
There are many different types of LANs, withEthernetsbeing the most common forPCs.
MostApple Macintosh networks are based onApple'sAppleTalk network system, which
is built into Macintosh computers.
The following characteristics differentiate one LAN from another:
1. Topology: The geometric arrangement of devices on the network. For example,devices can be arranged in a ring or in a straight line.
2. Protocols: The rules and encoding specifications for sending data. The protocolsalso determine whether the network uses apeer-to-peer orclient/server
architecture.
3. Media: Devices can be connected bytwisted-pair wire,coaxial cables,orfiberoptic cables. Some networks do without connecting media altogether,
communicating instead via radio waves.
http://en.wikipedia.org/wiki/Communications_protocolhttp://en.wikipedia.org/wiki/Network_topologyhttp://en.wikipedia.org/wiki/Computer_network_programminghttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Internet_protocol_suitehttp://www.webopedia.com/TERM/C/computer.htmlhttp://www.webopedia.com/TERM/N/network.htmlhttp://www.webopedia.com/TERM/S/system.htmlhttp://www.webopedia.com/TERM/W/wide_area_network_WAN.htmlhttp://www.webopedia.com/TERM/W/workstation.htmlhttp://www.webopedia.com/TERM/P/personal_computer.htmlhttp://www.webopedia.com/TERM/N/node.htmlhttp://www.webopedia.com/TERM/C/CPU.htmlhttp://www.webopedia.com/TERM/E/execute.htmlhttp://www.webopedia.com/TERM/P/program.htmlhttp://www.webopedia.com/TERM/A/access.htmlhttp://www.webopedia.com/TERM/D/data.htmlhttp://www.webopedia.com/TERM/D/device.htmlhttp://www.webopedia.com/TERM/U/user.htmlhttp://www.webopedia.com/TERM/L/laser_printer.htmlhttp://www.webopedia.com/TERM/E/e_mail.htmlhttp://www.webopedia.com/TERM/C/chat.htmlhttp://www.webopedia.com/TERM/E/Ethernet.htmlhttp://www.webopedia.com/TERM/P/PC.htmlhttp://www.webopedia.com/TERM/M/Macintosh_computer.htmlhttp://www.webopedia.com/TERM/A/Apple_Computer.htmlhttp://www.webopedia.com/TERM/A/AppleTalk.htmlhttp://www.webopedia.com/TERM/T/topology.htmlhttp://www.webopedia.com/TERM/T/topology.htmlhttp://www.webopedia.com/TERM/P/protocol.htmlhttp://www.webopedia.com/TERM/P/protocol.htmlhttp://www.webopedia.com/TERM/P/peer_to_peer_architecture.htmlhttp://www.webopedia.com/TERM/C/client_server_architecture.htmlhttp://www.webopedia.com/TERM/C/client_server_architecture.htmlhttp://www.webopedia.com/TERM/M/media.htmlhttp://www.webopedia.com/TERM/M/media.htmlhttp://www.webopedia.com/TERM/T/twisted_pair_cable.htmlhttp://www.webopedia.com/TERM/C/coaxial_cable.htmlhttp://www.webopedia.com/TERM/F/fiber_optics.htmlhttp://www.webopedia.com/TERM/F/fiber_optics.htmlhttp://www.webopedia.com/TERM/F/fiber_optics.htmlhttp://www.webopedia.com/TERM/F/fiber_optics.htmlhttp://www.webopedia.com/TERM/C/coaxial_cable.htmlhttp://www.webopedia.com/TERM/T/twisted_pair_cable.htmlhttp://www.webopedia.com/TERM/M/media.htmlhttp://www.webopedia.com/TERM/C/client_server_architecture.htmlhttp://www.webopedia.com/TERM/C/client_server_architecture.htmlhttp://www.webopedia.com/TERM/P/peer_to_peer_architecture.htmlhttp://www.webopedia.com/TERM/P/protocol.htmlhttp://www.webopedia.com/TERM/T/topology.htmlhttp://www.webopedia.com/TERM/A/AppleTalk.htmlhttp://www.webopedia.com/TERM/A/Apple_Computer.htmlhttp://www.webopedia.com/TERM/M/Macintosh_computer.htmlhttp://www.webopedia.com/TERM/P/PC.htmlhttp://www.webopedia.com/TERM/E/Ethernet.htmlhttp://www.webopedia.com/TERM/C/chat.htmlhttp://www.webopedia.com/TERM/E/e_mail.htmlhttp://www.webopedia.com/TERM/L/laser_printer.htmlhttp://www.webopedia.com/TERM/U/user.htmlhttp://www.webopedia.com/TERM/D/device.htmlhttp://www.webopedia.com/TERM/D/data.htmlhttp://www.webopedia.com/TERM/A/access.htmlhttp://www.webopedia.com/TERM/P/program.htmlhttp://www.webopedia.com/TERM/E/execute.htmlhttp://www.webopedia.com/TERM/C/CPU.htmlhttp://www.webopedia.com/TERM/N/node.htmlhttp://www.webopedia.com/TERM/P/personal_computer.htmlhttp://www.webopedia.com/TERM/W/workstation.htmlhttp://www.webopedia.com/TERM/W/wide_area_network_WAN.htmlhttp://www.webopedia.com/TERM/S/system.htmlhttp://www.webopedia.com/TERM/N/network.htmlhttp://www.webopedia.com/TERM/C/computer.htmlhttp://en.wikipedia.org/wiki/Internet_protocol_suitehttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Computer_network_programminghttp://en.wikipedia.org/wiki/Network_topologyhttp://en.wikipedia.org/wiki/Communications_protocol -
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5. Metropolitan Area Network (MAN)
A large computer network which extends to a city or to a large university campus is
termed as metropolitan area network or MAN. The purpose of MAN (Metropolitan Area
Network) is to provide the link to the internet in the long run. A MAN (Metropolitan Area
Network) usually incorporates a number of LANs to form a network. This large network
MANs (Metropolitan Area Network) backbone comprises of an optical fiber set-up.
5.1. Types of MAN (metropolitan Area Network) Technologies
Most widely used technologies to develop a MAN (Metropolitan Area Network) network
are FDDI (fiber distribution data interface), ATM (Asynchronous Transfer Mode) and
SMDS (switched multi megabit data service).ATM (Asynchronous Transfer Mode) is the
most frequently used of all. ATM (Asynchronous Transfer Mode) is a digital data transfer
technology. It was developed in 1980 to improve the transportation of real time data over
a single network. ATM (Asynchronous Transfer Mode) works just like cell relay system,
where data is separated in the form of fixed equal sized packets and is transferred
overtime. The purpose of ATM (Asynchronous Transfer Mode) was to access clear audio
and video results during a video conferencing. The attributes of ATM has enabled it to
become a base of wide area data networking. ATM (Asynchronous Transfer Mode)
combines the characteristics of circuit switching and packet switching, which allows it to
transfer even the real time data. FDDI is a standard for data transfer over LAN, which can
be extended to the range of approximately 200kms. FDDI can help support the data
transmission of many thousand users. This is the reason why it is referred to as the MAN
(Metropolitan Area Network) technology. FDDI uses optical fiber for its basic
infrastructure that is why it is referred to as fiber distribution data interface. When data is
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transferred through a connectionless service we use the technology named as SMDS.
Connectionless service implies that data is transferred by storing the information in the
header and it reaches its destination independently through any network. When the data is
transferred using the technology of SMDS, it also forms small data packets just like in
ATM. However SMDS allows the transmission of data over large geographical areas inthe form of datagrams(the data packets of an unreliable data service provider).
Nowadays MAN (Metropolitan Area Network) links are established using infrared and
microwave signals.
5.2How MAN works
MAN (Metropolitan Area Network) usually falls between LAN and WAN. It is generally
applied to connect geographically dispersed LANs. Therefore the goal of MAN is to
develop a communication link between two independent LAN nodes. A MAN
(Metropolitan Area Network) is usually established using optical fiber. The network is
established using routers and switches. A switch is a port which is active in handling the
filtration of data usually coming in the form of frames. Any switch acts as a dual port, at
one end it is handling filtration of data and at the other end managing connections. Router
is another device for facilitating the networks connection. Router helps the data packets to
identify the path to be taken. Hence in other words it keeps an eye on the data transfer.
MAN (Metropolitan Area Network) is usually operated over an area of up to 50kms.
5.3. Advantages of MAN (Metropolitan Area Network)
MAN (Metropolitan Area Network) falls in between the LAN and WAN. It therefore
increases the efficiency of handling data while at the same time saves the cost attached to
establish a wide area network. MAN (Metropolitan Area Network) offers centralized
management of data. It enables you to connect many fast LANs together. Telephone
companies worldwide have facilitated the transfer of data with the help of an underground
optical fiber network. These optical fibers increase the efficiency and speed of data
transfer. The optical fibers enable you to access a speed of almost 1000mbps. If you
develop a WAN of 1.45 mbps its cost is more than what it gives you. Whereas when you
establish metropolitan area network it offers you the speed of 1000mbps as a whole with
the lowest cost involved.
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6. Wide area network (WAN)
A wide area network (WAN) is a computer network that covers up a broad area
(i.e., any network whose communications links traverse metropolitan, regional, or
national boundaries. Unlike personal area networks (PANs), local area networks (LANs),
campus area networks (CANs), or metropolitan area networks (MANs) are usually
limited to a room, building, campus or particular metropolitan area (e.g. a town)
correspondingly.
WANs are used to connect LANs and other kinds of networks together, so that
users and computers in one place can communicate with users and computers in other
places. There are many WANs that are available to one particular organization working
privately. Others built by ISPs provide connections from LAN of an organization to the
Internet.
There are several options of WAN connectivity that are discussed below: Circuit
Switching Circuit switching is another WAN option. A circuit path is devoted at the end
paths. Dialup connections are perfect example of circuit switching, and it is less
expensive then leased lines. The speed of this network is 28-144 kbps and protocols are
PPP, ISDN.
Circuit Switching It is another option available in (WAN). A devoted circuit path
is created between end points. An excellent example is dialup connections. It is relatively
less expensive. The broadband range of this option is 28 - 144 kbps. Available protocols
include PPP, ISDN.
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Call relay is comparable to packet switching, but employs fixed length cells as an
alternative to changeable length packets. Statistics is confused into fixed-length cells, and
after that, it is elated to fundamental routes. It is finest for instantaneous exercise of voice
and information, the visual projection of call relay can be extensive, a paradigm of
protocol in the advertisement places is ATM.
Generally, WANs are frequently assembled by means of leased lines. At every
periphery of the leased line, a router is attached to the LAN on one side, and a centre
within the WAN on the other. Despite the fact that there has been utilization of leased
lines, WANs can in addition be ascertained by means of a modestly expensive circuit
switching, or packet switching mode. Network protocols comprise TCP/IP that conveys
transfer, and directing errands. Service providers to compel the connections that are
exercised in WANs regularly operate protocols together with Packet over SONET/SDH,
MPLs, ATM, and frame relay. X.25 was the chief untimely WAN protocol, and is
repeatedly acknowledged as the grandfather of frame relay as several of the essential
protocols, and utility of X.25 are offered in this contemporary period by frame relay.
Companies use these to minimize cost by cutting the need for travel, and
expensive long distance phone calls.These can diminish the charges of companies by
diminishing the necessity of journey, and also of high-priced extended distance phone
calls. In (WAN), you are able to contribute to data as well as video conferencing.
In (WAN), you can share data as well do as video conferencing. When
communication is being shared between computers, each operator can have the right to
use the same information at the same time. The use of a WAN also improves employee
output by increasing and accelerating work applications as well as dipping replication
across the WAN.
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7. Network Devices
Networking hardware or networking equipment typically refers to devices
facilitating the use of a computer network. Typically, this includes gateways, routers,
network bridges, switches, hubs, and repeaters. Also, hybrid network devices such as
multilayer switches, protocol converters, bridge routers, proxy servers, firewalls, network
address translators, multiplexers, network interface controllers, wireless network interface
controllers, modems, ISDN terminal adapters, line drivers, wireless access points,
networking cables and other related hardware
7.1 Router
A router is specializedcomputer connected to more than one network running
software that allows the router to move data from onenetwork to another. Routers operateat the network layer (OSI Model'slayer 3). The primary function of a router is to connect
networks together and keep certain kinds of broadcast traffic under control. There are
several companies that make routers:Cisco (Linksys),Juniper,Nortel (Bay Networks),
Redback,Lucent, 3Com,andHPjust to name a few.
7.1.1 Why do I need a Router?
Routers used in networks perform the following functions:
1. Restrict broadcasts to the LAN
http://www.inetdaemon.com/tutorials/computershttp://www.inetdaemon.com/tutorials/networking/lan/index.shtmlhttp://www.inetdaemon.com/tutorials/basic_concepts/network_models/osi_model/index.shtmlhttp://www.inetdaemon.com/tutorials/basic_concepts/network_models/osi_model/network.shtmlhttp://www.inetdaemon.com/tutorials/networking/lan/index.shtmlhttp://www.cisco.com/http://www.juniper.net/http://www.nortelnetworks.com/http://www.redback.com/http://www.lucent.com/http://www.hp.com/http://www.hp.com/http://www.lucent.com/http://www.lucent.com/http://www.redback.com/http://www.nortelnetworks.com/http://www.juniper.net/http://www.cisco.com/http://www.inetdaemon.com/tutorials/networking/lan/index.shtmlhttp://www.inetdaemon.com/tutorials/basic_concepts/network_models/osi_model/network.shtmlhttp://www.inetdaemon.com/tutorials/basic_concepts/network_models/osi_model/index.shtmlhttp://www.inetdaemon.com/tutorials/networking/lan/index.shtmlhttp://www.inetdaemon.com/tutorials/computers -
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2. Act as the default gateway.
3. Move (route) data between networks
4. Learn and advertise loop free paths
7.1.2. Restrict Broadcasts to the LAN
Networks (especially Ethernet networks) use broadcast communication at the
physical, datalinkand network layer.Network layerbroadcasts are transmissions sent to
all hosts using thenetwork layerprotocol (usuallyInternet Protocol [IP] or IPX).Network
broadcast communication is used to communicate certain kinds of information that makes
the network function (ARP,RARP,DHCP,IPX-SAP broadcasts etc.). Since several
devices could attempt to transmit simultaneously and cause collisions, it is preferable to
separate large sets of hosts into different broadcast domains using aswitch,or router.
As the number of hosts on thenetwork increases, the amount of broadcast traffic
increases. If enough broadcast traffic is present on thenetwork,then ordinary
communication across thenetworkbecomes difficult.
To reduce broadcasts, a network administrator can break up anetwork with a large
number of hosts into two smallernetworks.Broadcasts are then restricted to each
network, and the router performs as the 'default gateway' to reach the hosts on the other
networks.
7.1.3. Act as the Default Gateway
Especially in today'snetworks,people are connecting to theInternet.When yourcomputer wants to talk to acomputer on anothernetwork,it does so by sending your data
to thedefault gateway (your local router). The router receives your data, looks for the
remote address of that far-offcomputer makes a routing decision and forwards your data
out a different interface that is closer to that remotecomputer.There could be several
routers between you and the remotecomputer,so several routers will take part in handing
off thepacket,much like a fireman's bucket brigade.
7.1.4. Move (route) Data between Networks
Routers have the capability to move data from onenetwork to another. This
allows two networks managed by different organizations to exchange data. They create a
network between them and exchange data between the routers on that network. Because a
router can accept traffic from any kind of network it is attached to, and forward it to any
other network, it can also allow networks that could not normally communicate with each
other to exchange data. In technical terms, a token ringnetwork and an Ethernet network
can communicate over a serial network. Routers make all this possible.
A router can take in anEthernet frame, strip the Ethernet data off, and then drop
theIP data into a frame of another type such as SDH/SONET, PDH/T1, ATM, and FDDI.
In this way a router can also perform 'protocol conversion', provided it has the appropriate
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hardware and software to support such a function. The whole point, however, is to
forward the data from the interface it receives data on, to another interface that
retransmits the received data onto another interface serving another network.
7.1.5. Learn and Advertise Loop-Free Paths
Routers can only learn and advertise routes dynamically if they are using a routing
protocol such as RIP, OSPF, EIGRP, IS-IS or BGP. Otherwise, a human has to configure
the routes by hand, which is called static routing.
Routing moves data on a hop-by-hop basis, what is often called 'hot potato'
routing. If a set of routers ends up passing the data around in a circle, without reaching
the destination, it's called a 'routing loop'. Packets get tossed around the loop until they
die of old age: their 'Time to Live' counter in the IP datagram is decremented as it passes
through each router and eventually it reaches zero and is discarded.
7.2. Hubs
On 10BaseT and 100BaseTX Ethernet networks larger than two computers, each
computer or printer (or other networked device) is connected to a hub. The hub is a small
box that gathers the
Signals from each individual device, optionally amplifies each signal, and then sends the
signal out to all other connected devices. Amplification helps to ensure that devices on
the network receive reliable information. You can think of an Ethernet hub like the hub of
a wheel, at the center of the spokes that connect each individual computer or printer.
Hubs are also called
Concentrators or repeaters. Hubs come in various sizes, the most common being 12-port
or 24port (meaning they can connect to 12 or 24 computers/printers/hubs). All of the
clients, servers, and peripherals connected to a hub (or to a set of interconnected hubs)
share the bandwidth (data delivery capacity) of your network. Technically, they form a
single
collision domainan area of an Ethernet network in which data sent to or from a device
may potentially collide with the data from other devices. As you add more clients,
servers, and peripherals to an Ethernet network, the number of
collisions increases and the performance of your network degrades. You can improve
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performance by isolating network traffic into many smaller collision domains.
Unfortunately, hubs cannot divide a network in this fashion; they simply repeat every
signal all to all connected devices. Instead, to divide networks into multiple collision
domains you can deploy switches, bridges, or routers. Each switch port, bridge port, or
router port forms a new collision domain.
7.3. Switches
Like a hub, an Ethernet switch is a device that gathers the signals from devices
that are connected to it, and then regenerates a new copy of each signal. Switches,
however, are more powerful than hubs and can substantially increase your networkperformance. In order to understand how they perform this magic, it is necessary to
understand first how they work.
Most common switches operate by learning the MAC addresses of all connected clients,
servers, and peripherals, and associating each address with one of its ports. When a
switch receives an incoming signal, it creates a temporary circuit between the sender and
receiver. The temporary circuit provides two important benefits.
First, the circuit allows the sender and receiver momentarily
First, the circuit allows the sender and receiver momentarily to exchange
information without intrusion from other devices on the network. That is, each pair of
communicating devices utilizes the full bandwidth (data carrying capacity) of the
network instead of sharing that bandwidth, as they do in unswitched Ethernet networks.
To say this another way, each switch port defines a collision domain containing only a
small number of devices and thereby helps provide maximum performance for Ethernet
networks.
Second, the circuit ensures that information travels directly between the communicating
computers.
This behavior differs markedly from unswitched Ethernet networks. In
unswitched networks, data from a transmitting computer is sent by the nearest hub to all
connected devices (not just to the recipient) and therefore congests parts of the network
needlessly.Like all network equipment, switches benefit your network only if they are
deployed in the proper manner. If your network is congested and if traffic pools in certain
areas, then you can improve network performance by replacing hubs with switches, or by
connecting hubs to switches in a hierarchical manner. (You can see a diagram of a school
network that uses a hierarchy of switches and hubs at
http://www.3com.com/nsc/500612c.html . The switches are gray boxes and the hubs are
black boxes labeled with numbers to indicate how many ports they have.) For the pools of
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heavy traffic, switches increase bandwidth while segregating the traffic from the rest of
the network. However, if your network is not congested or if your traffic patterns do not
create pools of congestion, then switches may actually cause your network performance
to deteriorate. This performance degradation occurs because switches examine the
information inside each signal on your network (to determine the addresses of the senderand receiver) and therefore process network information more slowly than hubs.
Recently, manufacturers have begun to offer switches that examine OSI level 3
(network routing) information such as that contained in the IP portions (rather than the
data link portions) of a network signal. Later in this chapter, you will discover that routers
also examine this information. Level 3 switches blur the distinction between switches and
routers. Level 3 switches can replace routers within your network or between your
network and the Internet (while level 2 switches can replace hubs, but not routers).
7.3.1. Types of Network Switch:
There are different types of networking switch based upon the form and the
configuration. On the basis of their form they are categorized into rack mounted, chassis
or catalyst switch etc. And on the basis of configuration they are differentiated into
managed, unmanaged, smart or enterprise managed switches.
7.3.2. Managed Switches:
A type of network switch in which different types of methods are used to manage
the different parts of the network and can able to upgrade the working and the
performance of the switch with the help of common methods of management is called as
the managed network switch.
7.3.3. Unmanaged Network Switch:Basically these networking switches are designed for those customers that are not
able to spend more money because those are less expensive. A type of network switch in
which interface is not involved is called as unmanaged network switches. They are
designed for the direct use.
7.3.4. Smart Switches:
Basically the smart network switches are the important types of managed switches
in which the specific management features are discussed. Typically these switches reused
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for the networking devices such as VLANs. They also increase the working ability of the
parts connected by the switches.
7.3.5. Advantages of Network Switch:
Due to the reliable and the easy working of the network switches to manage the
network by joining the different segments of the network. Some of the particular
advantages of the network switching are given below.
1. Network switches are very beneficial for the expenditure of the network and canalso helpful in decreasing the load from the systems individually
2. They are also helpful for the in maintaining and enhancing the performance of thenetwork using switches
3. In the networking data is transmitted in the form of the data packets and in thesecases there are more chances of collision between the packets but network
switches are also able to avoid the collision between the data grams
8. Types of VLAN's
VLAN membership can be classified by port, MAC address, and protocol type.
8.1. Layer 1 VLAN: Membership by Port
Membership in a VLAN can be defined based on the ports that belong to the VLAN. For
example, in a bridge with four ports, ports 1, 2, and 4 belong to VLAN 1 and port 3
belongs to VLAN 2 (seeFigure).
Port VLAN
1 1
2 1
3 2
4 1
Figure: Assignment of ports to different VLAN's.
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The main disadvantage of this method is that it does not allow for user mobility. If a user
moves to a different location away from the assigned bridge, the network manager must
reconfigure the VLAN.
8.2. Layer 2 VLAN: Membership by MAC Address
Here, membership in a VLAN is based on the MAC address of the workstation.
The switch tracks the MAC addresses which belong to each VLAN (seeFigure). Since
MAC addresses form a part of the workstation's network interface card, when a
workstation is moved, no reconfiguration is needed to allow the workstation to remain in
the same VLAN. This is unlike Layer 1 VLAN's where membership tables must be
reconfigured.
MAC Address VLAN
1212354145121 1
2389234873743 2
3045834758445 2
5483573475843 1
Figure: Assignment of MAC addresses to different VLAN's.
The main problem with this method is that VLAN membership must be assigned initially.
In networks with thousands of users, this is no easy task. Also, in environments where
notebook PC's are used, the MAC address is associated with the docking station and not
with the notebook PC. Consequently, when a notebook PC is moved to a different
docking station, its VLAN membership must be reconfigured.
8.3. Layer 2 VLAN: Membership by Protocol Type
VLAN membership for Layer 2 VLAN's can also be based on the protocol type
field found in the Layer 2 header (seeFigure).
Protocol VLAN
IP 1
IPX 2
Figure: Assignment of protocols to different VLAN's.
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8.4. Layer 3 VLAN: Membership by IP Subnet Address
Membership is based on the Layer 3 header. The network IP subnet address can
be used to classify VLAN membership (seeFigure).
IP Subnet VLAN
23.2.24 1
26.21.35 2
Figure: Assignment of IP subnet addresses to different VLAN's.
Although VLAN membership is based on Layer 3 information, this has nothing to
do with network routing and should not be confused with router functions. In this method,
IP addresses are used only as a mapping to determine membership in VLAN's. No other
processing of IP addresses is done.
In Layer 3 VLAN's, users can move their workstations without reconfiguring theirnetwork addresses. The only problem is that it generally takes longer to forward packets
using Layer 3 information than using MAC addresses.
8.5 Higher Layer VLAN's
It is also possible to define VLAN membership based on applications or service,
or any combination thereof. For example, file transfer protocol (FTP) applications can be
executed on one VLAN and telnet applications on another VLAN.
The 802.1Q draft standard defines Layer 1 and Layer 2 VLAN's only. Protocol
type based VLAN's and higher layer VLAN's have been allowed for, but are not defined
in this standard. As a result, these VLAN's will remain proprietary.
8.6. Types of Connections
Devices on a VLAN can be connected in three ways based on whether the
connected devices are VLAN-aware or VLAN-unaware. Recall that a VLAN-aware
device is one which understands VLAN memberships (i.e. which users belong to a
VLAN) and VLAN formats.
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8.6.1 Trunk Link
All the devices connected to a trunk link, including workstations, must be VLAN-
aware. All frames on a trunk link must have a special header attached. These special
frames are called tagged frames (seeFigure).
Figure: Trunk link between two VLAN-aware bridges.
8.6.2 Access Link
An access link connects a VLAN-unaware device to the port of a VLAN-aware
bridge. All frames on access links must be implicitly tagged (untagged) (seeFigure8).
The VLAN-unaware device can be a LAN segment with VLAN-unaware workstations or
it can be a number of LAN segments containing VLAN-unaware devices (legacy LAN).
Figure 8: Access link between a VLAN-aware bridge and a VLAN-unaware device.
8.6.3. Hybrid Link
This is a combination of the previous two links. This is a link where both VLAN-
aware and VLAN-unaware devices are attached (seeFigure9). A hybrid link can have
both tagged and untagged frames, but all the frames for a specific VLAN must be either
tagged or untagged.
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Figure9: Hybrid link containing both VLAN-aware and VLAN-unaware devices.
It must also be noted that the network can have a combination of all three types of links.
9. Frame Processing
A bridge on receiving data determines to which VLAN the data belongs either by
implicit or explicit tagging. In explicit tagging a tag header is added to the data. The
bridge also keeps track of VLAN members in a filtering database which it uses to
determine where the data is to be sent. Following is an explanation of the contents of the
filtering database and the format and purpose of the tag header .
9.1 Filtering Database
Membership information for a VLAN is stored in a filtering database. The
filtering database consists of the following types of entries:
9.2 Static Entries
Static information is added, modified, and deleted by management only. Entries
are not automatically removed after some time (ageing), but must be explicitly removed
by management. There are two types of static entries:
a) Static Filtering Entries: which specify for every port whether frames to be sent to a
specific MAC address or group address and on a specific VLAN should be forwarded or
discarded, or should follow the dynamic entry, and
b) Static Registration Entries: which specify whether frames to be sent to a specific
VLAN are to be tagged or untagged and which ports are registered for that VLAN.
9.3. Dynamic Entries
Dynamic entries are learned by the bridge and cannot be created or updated by
management. The learning process observes the port from which a frame, with a given
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source address and VLAN ID (VID), is received, and updates the filtering database. The
entry is updated only if all the following three conditions are satisfied:
a) this port allows learning,
b) the source address is a workstation address and not a group address, and
c) there is space available in the database.
Entries are removed from the database by the ageing out process where, after a
certain amount of time specified by management (10 sec --- 1000000 sec), entries allow
automatic reconfiguration of the filtering database if the topology of the network changes.
There are three types of dynamic entries:
a) Dynamic Filtering Entries: which specify whether frames to be sent to a specific MAC
address and on a certain VLAN should be forwarded or discarded.
b) Group Registration Entries: which indicate for each port whether frames to be sent to a
group MAC address and on a certain VLAN should be filtered or discarded. These entries
are added and deleted using Group Multicast Registration Protocol (GMRP). This allows
multicasts to be sent on a single VLAN without affecting other VLAN's.
c) Dynamic Registration Entries: which specify which ports are registered for a specific
VLAN. Entries are added and deleted using GARP VLAN Registration Protocol (GVRP),
where GARP is the Generic Attribute Registration Protocol.
GVRP is used not only to update dynamic registration entries, but also tocommunicate the information to other VLAN-aware bridges.
In order for VLAN's to forward information to the correct destination, all the
bridges in the VLAN should contain the same information in their respective filtering
databases. GVRP allows both VLAN-aware workstations and bridges to issue and revoke
VLAN memberships. VLAN-aware bridges register and propagate VLAN membership to
all ports that are a part of the active topology of the VLAN. The active topology of a
network is determined when the bridges are turned on or when a change in the state of the
current topology is perceived. The active topology is determined using a spanning tree
algorithm which prevents the formation of loops in the network by disabling ports. Once
an active topology for the network (which may contain several VLAN's) is obtained, the
bridges determine an active topology for each VLAN. This may result in a different
topology for each VLAN or a common one for several VLAN's. In either case, the VLAN
topology will be a subset of the active topology of the network (seeFigure 10).
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Figure: Active topology of network and VLAN A using spanning tree algorithm.
9.4. Tagging
When frames are sent across the network, there needs to be a way of indicating to
which VLAN the frame belongs, so that the bridge will forward the frames only to those
ports that belong to that VLAN, instead of to all output ports as would normally have
been done. This information is added to the frame in the form of a tag header. In addition,
the tag header:
i) Allows User Priority Information To Be Specified,
ii) Allows Source Routing Control Information To Be Specified, And
iii) Indicates The Format Of Mac Addresses.
Frames in which a tag header has been added are called tagged frames. Tagged
frames convey the VLAN information across the network. The tagged frames that are sent
across hybrid and trunk links contain a tag header. There are two formats of the tag
header:
i) Ethernet Frame Tag Header: The ethernet frame tag header (see Figure11) consists of a
tag protocol identifier (TPID) and tag control information (TCI).
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Figure11: Ethernet frame tag header.
ii) Token Ring and Fiber Distributed Data Interface (FDDI) tag header: The tag headers
for both token ring and FDDI networks consist of a SNAP-encoded TPID and TCI.
Figure12: Token ring and FDDI tag header.
TPID is the tag protocol identifier which indicates that a tag header is following and TCI
(seeFigure 13) contains the user priority, canonical format indicator (CFI), and the
VLAN ID.
Figure13: Tag control information (TCI).
User priority is a 3 bit field which allows priority information to be encoded in the
frame. Eight levels of priority are allowed, where zero is the lowest priority and seven is
the highest priority. How this field is used is described in the supplement 802.1p.
The CFI bit is used to indicate that all MAC addresses present in the MAC data
field are in canonical format. This field is interpreted differently depending on whether it
is an ethernet-encoded tag header or a SNAP-encoded tag header. In SNAP-encoded
TPID the field indicates the presence or absence of the canonical format of addresses. In
ethernet-encoded TPID, it indicates the presence of the Source-Routing Information (RIF)
field after the length field. The RIF field indicates routing on Ethernet frames.
The VID field is used to uniquely identify the VLAN to which the frame belongs.
There can be a maximum of (212- 1) VLAN's. Zero is used to indicate no VLAN ID, but
that user priority information is present. This allows priority to be encoded in non-priority
LAN's.
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10. Conclusion
As we have seen there are significant advances in the field of networks in the form of
VLAN's which allow the formation of virtual workgroups, better security, improved
performance, simplified administration, and reduced costs. VLAN's are formed by thelogical segmentation of a network and can be classified into Layer1, 2, 3 and higher
layers. Only Layer 1 and 2 are specified in the draft standard 802.1Q. Tagging and the
filtering database allow a bridge to determine the source and destination VLAN for
received data. VLAN's if implemented effectively, show considerable promise in future
networking solutions.
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11. References
1) David Passmore, John Freeman, ``The Virtual LAN Technology Report,'' March 7,1997,http://www.3com.com/nsc/200374.html
A very good overview of VLAN's, their strengths, weaknesses, and implementation
problems.
2) IEEE, ``Draft Standard for Virtual Bridge Local Area Networks,'' P802.1Q/D1, May
16, 1997,
This is the draft standard for VLAN's which covers implementation issues of Layer 1 and
2 VLAN's.
3) Mathias Hein, David Griffiths, Orna Berry, ``Switching Technology in the Local
Network: From LAN to Switched LAN to Virtual LAN,'' February 1997,Textbook explanation of what VLAN's are and their types.
7) Susan Biagi, "Virtual LANs," Network VAR v4 n1 p. 10-12, January 1996,
An Overview of VLAN's, advantages, and disadvantages.
8) David J. Buerger, ``Virtual LAN cost savings will stay virtual until networking's next
era,'' Network World, March 1995,
A short summary on VLAN's.
9) IEEE, ``Traffic Class Expediting and Dynamic Multicast Filtering,'' 802.1p/D6, April
1997,
This is the standard for implementing priority and dynamic multicasts. Implementation of
priority in VLAN's is based on this standard.
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12. Abbreviations
CFI - Canonical Format Indicator FDDI - Fiber Distributed Data Interface FTP - File Transfer Protocol GARP - Generic Attribute Registration Protocol GMRP - Group Multicast Registration Protocol GVRP - GARP VLAN Registration Protocol IEEE - Institute of Electrical and Electronic Engineers LAN - Local Area Network MAC - Media Access Control RIF - Source-Routing Information TCI - Tag Control Information TPID - Tag Protocol Identifier VID - VLAN ID VLAN - Virtual Local Area Network