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

12.1. Overview and Scope of the Standard

As with most communications standards, 802.1Q provides both the architecture and a minimally required set of functions needed to support the target applications. Q-compliant switches can be built that provide all of the application behaviors and benefits discussed in Chapter 11: traffic isolation, ease of moves/adds/changes (software patch panels), and so on. However, the standard itself is more of a toolbox than an implementation guide. The architecture and functionality specified supports an almost unlimited range of potential VLAN applications — including all of the ones we have examined and more — yet there are no recipes provided to build any particular application feature and no requirement to support any specific application environment. This approach (which is the same one used in most network standards) provides for interoperability among vendors without restricting their ability to provide products with different capabilities for different market segments. In addition, such flexibility provides the hooks to support future application environments not yet conceived.

CORRECTING A COMMON MISCONCEPTION The 802.1Q standard specifies a default behavior that is port-based; that is, in the absence of any other implementation-specific rules, a Q-compliant switch associates an untagged received frame with a VLAN identifier based on the port on which the frame arrived. Because this port-based behavior is the only VLAN association rule even ...