The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

11.2. VLAN Concepts

If a catenet is a set of stations that are able to communicate transparently at the Data Link layer, then a VLAN can be seen as being a proper subset of the catenet. A VLAN comprises a set of stations (defined by the VLAN association rules in effect) together with the links and switches needed to interconnect them. A station may be a member of multiple VLANs, depending on the VLAN association rules, the capabilities of the stations and switches deployed, and the nature of the protocols and applications operating within the station.

From the previous section, you can see that VLAN technology can provide real end-user benefits. In this section, we look at the technical and operational aspects of VLANs that are needed to achieve these benefits. To this end, we consider four important mechanisms:

• VLAN tagging

• VLAN awareness

• VLAN association rules

• Frame distribution

As we can see from the various VLAN applications described earlier (and many more that will become evident), a VLAN is a logical grouping of entities in a catenet, but there is no restriction on the nature of the entities so grouped. A VLAN can comprise a set of logically related stations (for example, a distributed workgroup), a set of Network layer protocol entities (i.e., an IP subnet or IPX network), a set of high-level application entities (for example, a LAN videoconference), and so on. Clearly, ...