1 25\10\2010 unit-v connecting lans unit – 5 connecting devicesconnecting devices backbone...

$: 1 25\10\2010 Unit-V Connecting LANs Unit – 5 Connecting DevicesConnecting Devices Backbone NetworksBackbone Networks Virtual LANsVirtual LANs$
1 25\10\2010 Unit-V Connecting LANs

Unit – 5 •Connecting DevicesConnecting Devices•Backbone NetworksBackbone Networks•Virtual LANsVirtual LANs


CONNECTING DEVICESCONNECTING DEVICES

In this section, connecting devices are divided into five In this section, connecting devices are divided into five different categories based on the layer in which they different categories based on the layer in which they operate in a network.operate in a network.

Passive Hubs

Active HubsBridges

Two-Layer Switches

Routers

Three-Layer Switches

Gateways


Five categories of connecting devices based on the layer in which they operate Five categories of connecting devices based on the layer in which they operate in a networkin a network

1.1.Those which operate below the physical layer (passive hub)Those which operate below the physical layer (passive hub)

2.2. Those which operate at the physical layer (repeater or an active hub)Those which operate at the physical layer (repeater or an active hub)

3.3.Those which operate at the physical & data link layer (bridge)Those which operate at the physical & data link layer (bridge)

4.4.Those which operate at he physical & data link &network layer (router or 3 Those which operate at he physical & data link &network layer (router or 3 layer switch)layer switch)

5.5.Those which operate at all the five layer (a gateway)Those which operate at all the five layer (a gateway)

Connecting Devices


is a connector

It connects the wires coming from different branches.

same or different cable types

pass on every message

used to connect LANs of similar technology, or to extend the distance of one LAN

Passive Hub


is a device that operates only in physical layer

It does not connects two LANs, it connects segments of a LAN.

It is used to extend the physical length of a LAN

Repeater


forwards every frame; it has no filtering capability.

It does not amplify the signal it regenerates the signal

Repeaters


are a multiport repeater

It is usually used to create connections between stations in a physical star topology

limited distance between devices

no protocol or rate conversion

no error detection

does not filter

Active Hubs


HUB Devices

HUB

Repeater/Amplifier

Active Hubs


A hierarchy of hubs

Active Hubs


Operates in both the physical and the data link layer.

The difference between bridge and repeater is that, it has filtering capability.

Can physical (MAC) addresses contained in the frame.

connect two LAN segments that use the same data link and network protocol

same or different cable types

forward only those messages that need to go out (filtering)

“learn” whether to forward packets

internal routing table

combination of “black box” hardware and software

A bridge has a table used in filtering decisions.

A bridge does not change the physical (MAC) addresses in a frame.

Bridges


A bridge connecting two LANsBridges


There are three types of bridges:• Simple bridge• Learning bridge• Multiport bridge

Transparent Bridge• A Transparent Bridge is bridge in which the stations are

completely unaware of the bridge’s existence

Transparent bridges must meet three criteria:

1. Frames must be forwarded from one station to another

2. Forwarding table must be automatically updated

3. Loops in the system must be prevented.

Bridges


Learning:• Bridges have forwarding tables.• System administrator manually enter each table during

bridge setup• If a station is added, or deleted or MAC address changed

which is not a rare event (Inserting a new network card). • A solution to this is to map address to ports automatically.• In this case table is dynamic in which bridge gradually

updates addresses to ports automatically.

Bridges


A learning bridge and the process of learningA sends frame to D, it flood in all ports but it notices A is in port 1

When E sends a frame to A it forwards only on port 1 and notices E is in port 3

B sends a frame to C it floods in all ports and notices B is in port 1

Bridges


Loop problemNetworks usually have redundant bridges to make system more reliable

If bridge fails another bridge takes over until the failed one is repaired or replaced

Redundancy can create loops in the system, which is very undesirable.

Bridges


Loop problem in a learning bridge

Bridges


Spanning TreeIn a graph theory, a spanning tree is graph in which there is no loop but all the elements of the graph are connected.

In this case, creating bridged network in which LAN can be reached from any other LAN through one path only.

Network consists of 4 LANS and 5 bridges

To find a spanning tree a cost (metric) is used.

Cost may be minimum hops, minimum path delay or path with maximum bandwidth.

Bridges


Bridges• The bridge with smallest ID is selected as root node.• Assuming B1 has the smallest ID• Bridge to LAN COST is 1 and LAN to Bridge cost is 0


Finding the shortest paths and the spanning tree in a system of bridges

Bridges


Forwarding and blocking ports after using spanning tree Forwarding and blocking ports after using spanning tree algorithmalgorithm

Bridges


Connect more than two LAN segments that use the same data link and network protocol.

Switches

• Two Layer switch

• Three Layer switch

Two Layer switch

• Performs at physical and data link layer

• Ex Bridge, can connect a few LANs together

• Makes filtering decision based on MAC address

Three Layer switch

• Performs at Network layer

• Ex, Routers

Switches


Cut-through switches

• use circuit-switching to immediately connect the port with the incoming message to the correct outgoing port

• very fast as decisions are done in hardware

• outgoing packet is lost if port is in use

Store-and-forward switches

• copy the incoming packet to memory prior to processing the destination address -- transmit it when the outgoing port is ready

Switches


Switches Interconnecting

Wing C Wing C

Wing A Wing B

First Floor Switch

Switches


Connect two or more LANs that use the same or different data link protocols, but the same network protocol.

Same or different cable types

Operate at the network layer

Forward only messages that need to go out

Routers use internetwork address (IP or Logical address)

Internal routing tables

Only processes messages addressed to it

Routers


Routers Interconnecting

\

Router

Ethernet

LAN2

Token Ring

LAN1

X.25 Network

the “cloud”

Routers


Routers connecting independent LANs and WANs

Routers


is normally a computer that operates in all five layers of the Internet or seven layers of OSI model

complex machines that are interfaces between two or more dissimilar networks

Connecting device between tow internetworks that use different models (one with OSI and other with Internet model)

connect two or more LANs that use the same or different data link layer, network layer, and cable types

forwards only those messages that need to go out

a combination of both hardware and software

translates one network protocol to another

translates data formats

translates open sessions between application programs

Gateways can provide security

Gateways


BACKBONE NETWORKSBACKBONE NETWORKS

A backbone network allows several LANs to be A backbone network allows several LANs to be connected. In a backbone network, no station is directly connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs. LAN, and the backbone connects the LANs.

Bus BackboneStar BackboneConnecting Remote LANs


In a bus backbone, the topology of the backbone is a bus.

Normally used as a distribution backbone to connect different buildings in an organization.

Each building may have single LAN or another backbone(star).

Ex: single or multiple floor buildings on a campus, each single floor usually has a single LAN, each multiple floor building has a backbone (star) that connect each LAN. A bus backbone can interconnect these LANs and backbone.

Bus Backbone


Bus Backbone

Frame within a LAN will not be allowed go out by bridge.

If a station needs to send frame to station in another LAN the bridge passes the frame to the backbone which is received by the appropriate bridge and is delivered to the destination LAN


In a star backbone, the topology of the backbone is a star;

the backbone is just one switch.

Star backbone are mostly used as backbone inside a building.

In a multifloor building, there is one LAN for each floor, and star backbone connects these LANs.

Star Backbone


Connecting remote LANsA point-to-point link acts as a LAN in a remote backbone connected by remote bridges.

Company has several offices need to be connected.


VIRTUAL LANsVIRTUAL LANs

Virtual local area networkVirtual local area network (VLAN) is defined as a local (VLAN) is defined as a local area network configured by software, not by physical area network configured by software, not by physical wiring.wiring.

MembershipConfiguration

Communication between Switches

IEEE Standard

Advantages


A switch connecting three LANsA switch connecting three LANs

10 stations grouped into 3 LANs, 10 stations grouped into 3 LANs,

If two engineers need to move from grop1 to group3 , rewiring is needed If two engineers need to move from grop1 to group3 , rewiring is needed

Connecting remote LANs


A switch using VLAN softwareA switch using VLAN software

Connecting remote LANs


Two switches in a backbone using VLAN softwareTwo switches in a backbone using VLAN softwareConnecting remote LANs


Characteristic to group a stations in a VLAN

Port Numbers:

• Switch port numbers. Ex stations connecting to ports 1,2,3, 7 to VLAN1 and stations connecting to ports 4,10, and 12 belong to VLAN2

MAC addresses:

• 48 bit MAC address

IP addresses: 32 bit IP address

Combination:

Membership


How are the stations are grouped into different VLANs

Manual configuration:

• Network administrator uses VLAN software to manually assign the stations into different VLANs at setup, based on characteristic. Manually means administrator types the port numbers, IP address …

Automatic configuration:

• Administrator groups stations based on the project working.

Configuration

1 25\10\2010 unit-v connecting lans unit – 5 connecting devicesconnecting devices backbone...

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