4.2 VLAN Types
4.2.1 VLAN boundaries
The number of VLANs in the switch block may vary greatly, depending on several factors. This includes traffic patterns, types of applications, network management needs, and group commonality. In addition, an important consideration in defining the size of the switch block and the number of VLANs is the IP addressing scheme.

For example, suppose your network uses a 24-bit mask to define a subnet. Given this criterion, a total of 254 host addresses are allowed in one subnet. Because a one-to-one correspondence between VLANs and IP subnets is strongly recommended, there can be no more than 254 devices in any one VLAN. It is further recommended that VLANs should not extend outside of the Layer 2 domain of the distribution switch. As you can see in the Figure, with many users in the building under the recommended constraints, a minimum of four VLANs will be in the switch block.

When scaling VLANs in the switch block, there are two basic methods of defining the VLAN boundaries:

  • End-to-end VLANs
  • Local VLANs