LAN Design Broadcast and Collision Domains

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

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... Gather & establish design goals based on user requirements Determine data traffic patterns now & in the future Define Layer 1, 2, & 3 devices & the LAN/WAN topologies 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 Collision Detection Micro segmentation Bandwidth v. Broadcast domains Function & placement of Servers

MAC Address Contains 48-bit destination address field. Who is this frame for? 00-C0-F0-56-BD-97 “D: It is for me”

MAC Address How will all other NICs handle the frame? Drop it out.

Special MAC Address Who is this frame for? “Hey everybody” FF-FF-FF-FF-FF-FF “Hey everybody”

Broadcast MAC Address FF-FF-FF-FF-FF-FF 48 bits, all 1s All NICs copy the frame & send it up the stack

Broadcast Frames Necessary for network function Used for finding services: “Hey, is there a server out there?” Advertising services: “Hey, I’m a printer you can use.”

Collision Domain Network region in which collisions are propagated. Repeaters and hubs propagate collisions. Bridges, switches and routers do not.

Reducing Collisions Collision frequency can be kept low by breaking the network into segments bounded by: bridges switches routers

Broadcast Domain Network region in which broadcast frames are propagated. Repeaters, hubs, bridges, & switches propagate broadcasts. Routers don’t (Stops broadcasts).

Reducing Broadcasts Broadcasts are necessary for network function. Some devices and protocols produce lots of broadcasts. Broadcast frequency can be kept manageable by limiting the LAN size. LANs can then be cross-connected by routers to make a larger internetwork.

Shared Ethernet A single segment that is shared among all connected NICs. A single collision domain. The segment includes repeaters and hubs. Sometimes called a “single flat Ethernet”.

Switched Ethernet Consists of a several segments, each of which is shared by NICs attached to it. The network is segmented into several collision domains. Bridges, switches, and routers create the segment and collision domain boundaries. Segments may contain hubs and repeaters.

Micro segmented Switched Ethernet Each user NIC is connected directly to a switch port. Provides one switched segment to each connected NIC. No sharing. No collisions.

Identify the collision domains and broadcast domains?

Identify the collision domains and broadcast domains?

Identify the collision domains and broadcast domains?

Identify the collision domains and the broadcast domains? Routers connect separate networks. One broadcast domain per router interface.

Intranets & Collisions Intranets are internal to the organization and are not accessible by the public over the Internet. Intranet Servers provide access to only authorized users. This has caused an increase in needed bandwidth. Therefore, when designing a network you must address... Server privileges Providing 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.

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.

Reminder Collisions Broadcasts spread throughout a LAN segment spread across hubs & repeaters are stopped by switches & bridges Broadcasts spread throughout an entire LAN spread across hubs, switches, bridges are stopped only by routers

Summary

Network Design Methodology Table of Contents End Slide Show

Gathering & Analyzing Requirements Gathering data about the organization includes:

Network Availability Network design seeks to provide the greatest availability for the least cost. Factors that affect availability include... Throughput (amount of data) Response time Access to resources

Physical Topologies Most LANs now days use the star/extended star physical topology which typically uses the Ethernet 802.3 standard. Why? Because it is the most popular topology. The next three sections, evaluate the extended star by layers.

Layer 1 Design Table of Contents End Slide Show

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 there to the patch panel, called the HCC (Horizontal cross connect), 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) Graphic

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 (Main Distribution Facility)- A room that will be established as the central point to which all LAN cabling will be terminated. Workgroup Servers--supports a specific set of users file serving such as specialized databases should be place in the IDF (Intermediate distribution facilities) closest to users Graphic

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?

Layer 1 Logical Documentation Layer 1 logical documentation is concerned with... exact location of MDF/IDF type & quantity of cabling room locations & # of cable 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.

Layer 2 Design Table of Contents End Slide Show

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).

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.

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.

Layer 3 Design Table of Contents End Slide Show

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 VLAN capable switches help routers contain broadcasts. The graphic shows two broadcast domains. Notice there are also two subnets. 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.

Logical & Physical Network Maps After determining your Layer 1, 2, and 3 design, you can create your addressing (logical) and physical maps. These are important because they: Give a snapshot of the network Show subnet mask info Help in troubleshooting