Hierarchical Network Design

  • Three Layer Model:
    • Access layer: Where end users are connected. For intra-vlan routing.
    • Distribution Layer: where access layer switches are aggregated. For inter-VLAN routing
    • Core Layer: where distribution layer switches are aggregated. Center to all users.
  • Access layer;
    • Low cost per port
    • High port density
    • Scalable uplinks to higher layers.
    • Resiliency through multiple uplinks.
    • User access functions like VLAN, traffic and protocol filter and QOS.
  • Distribution Layer:
    • High L3 throughput for packet handling.
    • Access list, packet filters and Qos features.
    • Scalable and resilient high-speed links to access and core layers.
    • Acts as L3 boundary for access VLANs. Broadcast shouldn’t travel across Distribution layer.
  • Core Layer:
    • Very high L3 throughput.
    • Advanced QOS and L3 protocol functions.
    • Redundancy and resilience for HA.
  • Switch Block:
    • Collection of access layer switches together with distribution switches(2).
    • Sized based on traffic types and behavior, size and number of workgroups.
    • Need redundancy within switch block.
    • Broadcast from  a PC should be confine within switch block.
  • Core block:
    • An enterprise/campus network backbone.
    • Collapsed Core: Distribution and core layer are unified. Router performs both layer functions
    • Dual Core: Two core routers and switch blocks are connected to core routers in redundant fashion.
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