LAN Design


A hierarchical network design model, as opposed to a flat network design model, creates a more more functional network by differentiating network devices into core, distribution, and access layers, which creates a hierarchy of network devices and gives the network the following benefits:

•  Scalability – is improved because having distribution layer 3 switches segments the network, creates multiple broadcast domains, and distributes routing duties, this in turn allows the ability to add more access layer switches and add more host computers.
•  Redundancy – instead of having only one way out of the network, a hierarchical network design creates redundant, interconnected (meshed) distribution layer and core layer switches allowing more paths for traffic to flow.
•  Manageability – centralized management software can manage from the distribution layer
•  Enhanced bandwidth resources – greater network segmentation will lead to better bandwidth availability
•  Enhanced Security – having more than one distribution layer switch allows differentiated security policies and network security services

Hierarchical Network Design Model

  • Access Layer -This layer is used to connect end devices to the network such as PC’s, IP phones, and Printers. This layer may also include switches and routers especially workgroup switches which connect to end users. The Access Layer is also used to allow and control which devices can communicate on the network.
  • Distribution Layer -This is the layer where we apply filtering and apply network policies. The distribution layer controls the flow of the network, adds redundancy, and adds routing functions between VLANs.  High performance switches.
  • Core Layer – The core is the backbone of the network and it requires the highest level of bandwidth, typically fiber optic connections. The core connects to the ISP and has major routers and switches with redundancy. The core interconnects the distribution layer switches and routers.

Switch Attributes

  • Port Security – The ability to configure which host MAC addresses can be on a port, and shutdown ports if they are not the specified host MAC addresses.
  • PoE (power over ethernet) – The ability to use certain ethernet wire pairs for electrical power instead of data.
  • Link Aggregation – The ability to have multiple ports work together as uplink ports, effectively doubling and tripling uplink speeds.
  • QoS (quality of service)- The ability to distinguish and prioritize certain kinds of traffic like voice data.
  • Port Density – How many ports a switch has.
  • VLANs (virtual local area networks) – The ability to create VLANs and assign ports to separate VLANs
  • Access List Control – Layer 3 functionality. A layer 3 switch, which is a switch and a router combined is needed.

Switch Types

  • Fixed Configuration Switches -Cannot be changed or altered, port density is set.
  • Modular Switches – Can be altered by adding switch blade ports.
  • Stackable Switches – Special high speed backplane for connecting the switches together.

Switching Modes

  • Store and Forward – Slowest, most reliable
  • Cut Through Switching – Faster, but less reliabl
  • Fast Forward – Fastest, least reliable. The switch forwards the packet/frame once it has stripped off the destination MAC address.
  • Fragment Free – Second fastest. The switch forwards the packet after reading the first 64 bytes.

Author: Dan

Dan teaches computer networking and security classes at Central Oregon Community College.

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