1.4 Building-Block Approach
1.4.3
Scaling the switch block

Although the size of a switch block is flexible, certain factors limit its size. The number of switches that collapse into the distribution layer depends on several factors, such as:

  • Different types and patterns of traffic 
  • Amount of Layer 3 switching capacity at the distribution layer 
  • Number of users per access-layer switch 
  • Extent to which subnets need to traverse geographical locations within the network 
  • Size to which the Spanning-Tree domains should be allowed to grow

Sizing the switch block involves two main factors: 

  • Traffic types and behavior 
  • Size and number of workgroups

A switch block is too large if: 

  • A traffic bottleneck occurs in the routers at the distribution layer because of intensive CPU processing resulting from policy-based filters 
  • Broadcast or multicast traffic slows down the switches and routers