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| 1.3 |  | Building-Block Approach |
| 1.3.2 |  | 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