Scaling the Switch Block

Scaling the Switch Block
First introduced in Chapter 12, “The Campus Network,” switch blocks represent a switch or
group of switches providing access to users. These switches then connect to distribution layer
switches, which in turn handle routing issues and VLAN distribution.
To understand how many VLANs can be configured in a switch block, you must understand
the following factors:

Traffic patterns

Applications used

Network management

Group commonality

IP addressing scheme
Cisco recommends a one-to-one ratio between VLANs and subnets. For example, if you
have 2000 users in a building, then you must understand how they are broken up by subnets
to create your VLANs. If you had 1000 users in a subnet—which is ridiculous—you would
create only two VLANs. If you had only 100 users in a subnet, you would create about
20 VLANs or more.
It is actually better to create your broadcast domain groups (VLANs) and then create a subnet
mask that fits the need. That is not always possible, and you usually have to create VLANs
around an already-configured network