LAN Design.ppt

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Ram DantuUniversity of North Texas,

rdantu@unt.edu

Practical Networking

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Agenda

Nuts and Bolts of Internet Access, Edge, and Core Networks LAN Design End-user Protocols, Services and QoS Edge and Core Networks Performance

Bandwidth and Delay Security

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LAN Design (Access Network)

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LAN Design Goals

Critical to design is insuring a fast and stable network that will scale well as the organization grows

Design steps are...1. Gather & establish design goals based on

user requirements2. Determine data traffic patterns now & in the

future3. Define Layer 1, 2, & 3 devices & the LAN/WAN

topologies4. Document physical & logical network

implementation

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Establish the Design Goals

Although organizations are unique to the customer, the following requirements tend to be generic to all. The network must have... Functionality--speed and reliability Scalability--ability to grow without major

changes Adaptability--easily implements new

technologies Manageability--facilitates monitoring and

ease of management

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Critical Components of LAN Design With the emergence of high-speed

technologies and complex LAN technologies, the following critical components need addressing in design Function & placement of Servers Collision Detection Microsegmentation Bandwidth v. Broadcast domains

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Placement of Servers

Servers now perform special functions and can be categorized as either... Enterprise Servers--supports all users on

the network • DNS and mail servers• should be placed in the MDF

or... Workgroup Servers--supports a specific

set of users• file serving such as specialized databases• should be place in the IDF closest to users

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Intranets & Collisions

This has caused an increase in needed bandwidth. Therefore, design must address...

• Type of data to be accessed• Server privileges• Outfitting desktops with faster connectivity

– More processing power– 10/100Mbps NICs to provide migration to switched

technologies Collision detection and minimization has become a

major concern as users attempt to access the same server.

As we’ve seen, switches can provide dedicated bandwidth to minimize or eliminate collisions.

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Broadcasts & Segmentation

Layer 2 devices segment collision domains

Layer 3 devices segment broadcast domains

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Bandwidth v. Broadcast Domains A bandwidth domain

is shared by all devices on a single switched port.• Synonymous with

collision domain A broadcast domain is

shared by all devices on a single router interface.

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LAN Design Methodology

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Network Availability Network design seeks to

provide the greatest availability for the least cost.

Factors that affect availability include...• Throughput• Response time• Access to resources

In the graphic, what type of server is each and where should each be placed?

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Physical Topologies

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Layer 1 Design

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Ethernet Cable Runs The physical cabling (also called the cable plant) is

the most important Layer 1 issue to consider when designing a network.

Design issues include...• Type of cable to use (twisted-pair, coax, fiber)• Where to use each type (e.g. fiber on the backbone)• How far each run must travel before being terminated

(twisted-pair is limited to what distance?) In an existing LAN, a cable audit is performed to

determine where upgrading and/or replacement of bad cables is needed.

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MDF and IDF

Short for main distribution frame, a cable rack that interconnects and manages the telecommunications wiring between itself and any number of IDFs (Intermediate Distribution Frames). Unlike an IDF, which connects internal lines to the MDF, the MDF connects private or public lines coming into a building with the internal network. For example, an enterprise that encompasses a building with several floors may have one centralized MDF on the first floor and one IDF on each of the floors that is connected to the MDF.

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MDF & Other Acronyms

Whether the LAN is a star or extended star, the MDF is the center of the star.• From the workstation

to the telecommunications outlet, the patch cable should be no more than 3m.

• From their to the patch panel, called the HCC, no more than 90m.

• From the patch panel (the HCC) to the switch, no more than 6m.

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MDF & Other Acronyms When distances to the

MDF are more than 100m, an IDF is normally added.

The cable run from the IDF to the MDF is called the VCC and is usually fiber.

VCC is just another name for the backbone.

By adding more wiring closets (more IDFs), you create multiple catchment areas (Click of graphic button)

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10BaseT and 100BaseT Ethernet

100 BaseT (also called Fast Ethernet) is now the standard for connecting IDFs to the MDF. Although you can run Fast Ethernet over

100BaseT cabling (twisted pair), the distance limitation means fiber is most often used

The 100BaseT standard running on twisted pair is called 100BaseTX

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Layer 1 Logical Documentation Layer 1 logical

documentation is concerned with...• exact location of

MDF/IDF• type & quantity of

cabling• room locations & # of

drops• port numbers• cable labels

Notice Layer 1’s logical documentation shows nothing about logical addressing

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Layer 2 Design

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Common Layer 2 Devices The two most common

Layer 2 devices are...• Bridges and• LAN Switches

Both provide the added benefit of what?

Segmenting collision domains into microsegments.

Switches can also provide connections of unlike bandwidth (e.g., 100Mbps to the server & 10Mbps to workstations). This is called...?

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Sizing Collision Domains In a switched LAN

environment using hubs, the bandwidth of each switched port is shared by all the devices. Therefore, they also share the same collision domain.

To determine the bandwidth per host, simply divide the port’s bandwidth by the number of hosts (see graphic).

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Migrating to 100BaseT As long as your

workstations all have 10/100 NICs, increasing the bandwidth is easy.• Replace the hub with a

100Mbps capable hub and patch the HCC into a 100Mbps port on the switch.

• In addition, you can add another 100Mbps VCC from the IDF to the MDF, which provide 200 Mbps to the IDF’s switch.

• In the graphic, the red lines represent migrating to 100Mbps.

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Collision and Broadcast domains Hub

A hub receives a packet (chunk) of data (a frame in Ethernet lingo) at one of its ports from a PC on the network, it transmits (repeats) the packet to all of its ports and, thus, to all of the other PCs on the network.  If two or more PCs on the network try to send packets at the same time a collision is said to occur.

Switch An Ethernet switch automatically divides the network into

multiple segments, acts as a high-speed, selective bridge between the segments, and supports simultaneous connections of multiple pairs of computers which don't compete with other pairs of computers for network bandwidth.  It accomplishes this by maintaining a table of each destination address and its port.

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Layer 3 Design

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Routers and Design

Routers provide both physical and logical segmentation. Physically, routers

segment what? Logically, routers

segment according to Layer 3 addressing dividing the LAN into logical segments called subnets.

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Diagramming a LAN with Routers Notice in the graphic

that the two networks are kept separate by the router.

Each switch serves a different network regardless of the physical location of the devices.

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Logical & Physical Network Maps After determining your Layer 1, 2, and 3

design, you can create your addressing (logical) and physical maps. These are invaluable. They• Give a snapshot of the network• Show subnet mask info• Help in troubleshooting

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References

Slides adapted from Allan Johnson, CCNA