Content

| 2.3 |  | VLAN Types |
| 2.3.1 |  | VLAN boundaries |

Just as routing protocols are classified in various ways, VLANs can be classified in a variety of ways. VLANs are classified as local (geographic) or end-to-end (campus-wide). Alternatively, VLANs are classified as either port-based (static) or dynamic.

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 in the IP addressing scheme.

For example, suppose a 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. With many users spread across three departments in one building, four VLANs would be required under the recommended constraints.

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

- End-to-end VLANs
- Local VLANs