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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
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