Institute of Technology, Sligo Dept of Computing LAN Design Semester 3, Chapter 4

Table of Contents Design Goals & Components Network Design Methodology Layer 1 Design Layer 2 Design Layer 3 Design

Institute of Technology, Sligo Dept of Computing Design Goals & Components

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 requirements 2.Determine data traffic patterns now & in the future 3.Define Layer 1, 2, & 3 devices & the LAN/WAN topologies 4.Document physical & logical network implementation

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

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

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

Intranets & Collisions  Intranets are internal to the organization and are not accessible by the public over the Internet.  Intranet Servers use browsers to provide access to authorized users.  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 collsions.

Broadcasts & Segmentation  Layer 2 devices segment collision domains  Layer 3 devices segment broadcast domains

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.

Institute of Technology, Sligo Dept of Computing Network Design Methodology

Gathering & Analyzing Requirements  Gathering data about the organization includes the bullets in the graphic.

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?

Physical Topologies  In the CCNA curriculum, we concentrate on the star/extended star physical topology which typically uses the Ethernet standard.  Why? Because it is the most popular topology used in LANs.  The next three sections, evaluate the extended star by layers.

Institute of Technology, Sligo Dept of Computing Layer 1 Design

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.

MDF & Other 568A 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.

MDF & Other 568A 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)

What is the diameter of each of the three catchment areas?

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 10BaseT cabling (twisted pair), the distance limitation means fiber is most often used  The 100BaseT standard running on twisted paid is called 100BaseTX  On fiber, it is called what?  What is Gigabit Ethernet called?

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  The Logical Diagram and Cut Sheet are primary tools for design, but are crucial to the tech who is troubleshooting.

Institute of Technology, Sligo Dept of Computing Layer 2 Design

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...?

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).  In a pure switched LAN environment where each host has its own port, the size of the collision domain is 2. If running full-duplex, then the collision domain is eliminated. Why?

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.

Institute of Technology, Sligo Dept of Computing Layer 3 Design

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.

VLANs & Broadcast Domains  As we learned in Chapter 3, VLAN capable switches help routers contain broadcasts.  The graphic shows two broadcast domains.  Notice there is also two subnets. How do we know that?  The router provides communication between the two VLANs.

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.  To create another physical network in a structured Layer 1 wiring scheme, simply patch the HCC and VCC into the correct switch.

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