Network Design - Simple Explanation

 

• 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.